Ambient Temperature vs. Viscosity Choice

M

mark pruett

Joined
Jan 18, 2003
Messages
330
Location
Dallas, TX
Having been around here for nearly two decades, I've read more comments talking about how people run higher viscosities when it's hotter outside, and vice-versa. This makes a sort of intuitive sense, as oils, even multigrade ones, thin out as temperatures increase. And that phenomenon explains why we'd want lower "W" numbers on multigrades as well- that indicates thinner oils at start-up temps, which are considerably cooler than within a warmed up engine.

But the part I can't quite square is the thinking that somehow a engine that specifies using 30 weight (or 20, 40, etc...) and has a say... 203 degree thermostat is going to somehow require heavier oil when the ambient temp is high outside.

The reason this doesn't really make sense to me is because the difference between "comfortable" and "super-hot" is like 25-35 degrees Fahrenheit, and is *still* 100 degrees F below the operating temp of the vehicle. The assumption is that the cooling system is so feeble that driving it in say... 105F temps is going to overwhelm the cooling system and necessitate higher viscosity to offset those temps. This would be the same if we're talking bearings, cams, etc.... the cooling system would have to be nearly ineffective for the ambient temp to really matter, provided the oil is in the right spec, as it's trying to keep everything right around 203, and the *internal* heat generated by combustion, in the bearings, etc... is what needs to be shed. The only place ambient temp comes into it would be in being able to shed the heat that the cooling system is moving from inside the engine to outside, and that's affected by the ambient temp. Even then, the main thing is going to be the internal heat generation rate, not so much the ambient temp, provided it's not something absurd like 120F outside.

What am I missing, if anything?
 
mark pruett said:
Having been around here for nearly two decades, I've read more comments talking about how people run higher viscosities when it's hotter outside, and vice-versa. This makes a sort of intuitive sense, as oils, even multigrade ones, thin out as temperatures increase. And that phenomenon explains why we'd want lower "W" numbers on multigrades as well- that indicates thinner oils at start-up temps, which are considerably cooler than within a warmed up engine.

But the part I can't quite square is the thinking that somehow a engine that specifies using 30 weight (or 20, 40, etc...) and has a say... 203 degree thermostat is going to somehow require heavier oil when the ambient temp is high outside.

The reason this doesn't really make sense to me is because the difference between "comfortable" and "super-hot" is like 25-35 degrees Fahrenheit, and is *still* 100 degrees F below the operating temp of the vehicle. The assumption is that the cooling system is so feeble that driving it in say... 105F temps is going to overwhelm the cooling system and necessitate higher viscosity to offset those temps. This would be the same if we're talking bearings, cams, etc.... the cooling system would have to be nearly ineffective for the ambient temp to really matter, provided the oil is in the right spec, as it's trying to keep everything right around 203, and the *internal* heat generated by combustion, in the bearings, etc... is what needs to be shed. The only place ambient temp comes into it would be in being able to shed the heat that the cooling system is moving from inside the engine to outside, and that's affected by the ambient temp. Even then, the main thing is going to be the internal heat generation rate, not so much the ambient temp, provided it's not something absurd like 120F outside.

What am I missing, if anything?
Click to expand...
Here is what you are missing or what I think you are missing. Get an Infrared Gun and aim it at your oil pan when you get home. You can also install an Oil temperature Gauge if your car does not have 1. If the temp from an Infrared gun is not over 200 Degrees, this will mean your oil temp could be 20 degrees higher or so. You could also plug into the OB Port thing with a scanner and get a temp reading.

Realize that 2 thick of an oil can give you issues.

You live in Dallas, Texas just run a 5W-40 Oil.
 
Here are a few previous threads which may be of interest:

P

Thread 'Correct Viscosities Vs Ambient Temperatures'

I live in JHB,
temperatures here in winter go down to 5 in early mornings but warm up to average of 15-20degrees C.
Summer it averages from 15-20 in the mornings and gets sometimes hot maybe 25-35 degrees C.

I'm fully aware of thinner oils are far better,having better starting abilities and running smoother,with better fuel economy.
wink.gif


I'm currently running RL 5w40, its winter here, no problems but suggestions concerning viscosity ALL year round....
frown.gif
D

Thread 'Thicker oil for hotter ambient temp, Why?'

It's common for manufacturers to recommend thicker oil for higher ambient temperature. But if the coolant temperature gauge says the bike isn't running hotter, why different oil? Does the engine have hotter operating conditions in some way not indicated by coolant temperature? Or in the case of my air/oil cooled BMW temperature of whatever the dash indicator is measuring.

I wonder because temps have been high here lately (38+ C, 100+ F). And for the CRF1000L I just changed the oil on, the only recommended grade is 10W30. Yet on the africa twin forums some owner report that their local...
dlundblad

Thread 'Oil Weight and Ambient Temperatures'

I asked this before, but didnt get a straight answer.

Whats the point of running a thicker running weight in extreme heat? We see here that (some) Australians and folks in the Middle East like a 50 or 60 weight oil. Wouldn't the radiator keep oil temperature somewhat in check and prevent any oil related failures? I would also think an oil cooler would be a standard option for vehicles in these regions. We also see engines that spec a much thicker weight in Europe and the other mentioned regions while the identical US version will take a 20 or 30 weight oil. (It has been mentioned here...
4

Thread 'Does ambient air temperature matter or not for Oil'

I am greatly confused about one main thing: Air and climate temperature, vs grade of oil selected for a car. Please let me explain.

In almost any pre-2001 car manual (and some after that) i see, i see charts of temperature vs grades listed for the engine. Most charts list 10W-40 from around 10 or 20 degrees, those graphic arrow charts (the lowest ambient temperature i saw listed acceptable to 10W-40 was "4 degrees," i forget in which manual) - up to 100+. Then 10W-30 is listed as 0 or -5 on up, with 5W-30 going to approx. -20, on up. This is reason number one for the confusion.

Reason...
G

Thread 'Grades for high ambient temperature locations'

Living in the greater Phoenix, Arizona area we have winter temperatures down to -4C/25F and summer temperatures above 43C/110F. There are days when it gets above 46C/115F.

I'm convinced manufacturer's recommended grades of 5W20 or 5W30 are not appropriate at higher ambient temperatures. I suspect that 10W40 or 10W50 is appropriate.

I'm a long, long time Mobil 1 user but the only oil that fits that spec is a high mileage formulation ... in the US. In Europe, however, they produce a 10W60 for BMW-M cars!

I know Mobil 1 is available in 0W40 but the 0W winter rating is overkill in the...
L

Thread 'Viscosity and climate'

Im wondering why people tend to use a "thicker" or higher viscosity oil in hotter climate. The thermostat keeps the engine about the same operating temp whether in hotter or colder climates right?

To me, it is more of a decision of how much protection do you need vs effeciency savings...any thoughts?
S

Thread 'Viscosity vs. ambient temperature'

I live in southern California, where for most of the year it doesn't get below 60 degrees or so. However, in the winter, we do have some mornings where the temps are below freezing, evidenced by frost on the grass and windshields.

The recommended oil for my '97 F-150 is 5w-30, which is what I'm using now. The only thing that bothers me about this grade of motor oil is that in a lot of the UOA's, it seems to shear down to a 20-wt. in 5000 miles or less. My truck has over 200,000 miles on the clock, so I think a 30-wt. is probably a good choice.

I've read Motor Oil 101, and while I know...
O

Thread 'Viscosity Grade recommendation for Death Valley'

Death Valley is about 130F. 🔥

For my 0/5W-20 passenger cars, I prefer using a good 40 weight synthetic or at a minimum a very stout 30 unless I'm driving downhill.

Last 2 trips to Nevada, I used 40 and iirc, it wasn't even hotter than 95F.

What do you use or recommend?
  • Like
P

Thread 'Viscosity comparison - is it important?'

So here is my question:

If you look at oil comparisons there is a viscosity at 40 and 100 listed in the specs. There are several calculators around that will extrapolate that out for any operating temperature. The combination of the 40 and 100 can make a large difference in viscosity at operating temp if it is not 100. So here is my question - how important is the viscosity at operating temps (affect performance?), and what would be the normal operating temps for cars (100?), boats (80?), air cooled engined (no guess?).

Should I plot out the OEM recommended oil for temps, and verify my...
edhackett

Thread 'Interesting Temperature-Viscosity Chart'

Here's the recommended viscosity grades for given ambient temperatures for my 1991 BMW K100. This is a 1000cc, water cooled, inline four cylinder, with a four quart sump capacity.

Notice the complete lack of trust in multi-viscosity oils. They allow for it to shear back to its base viscosity. This is assuming mineral base and service grades SE, SF, SG.

SAE 20: -10 to 20C
SAE 30: 0 to 30C
SAE 40: 20 to 50C

SAE 10W30: -30 to 0C
SAE 10W40: -30 to 5C
SAE 10W50: -30 to 10C
SAE 15W40: -20 to 20C
SAE 15W50: -20 to 30C
SAE 20W40: -10 to 30C
SAE 20W50: -10 to 40C

Ed
M

Thread 'Ambient temperature vs. engine temperature'

I've read many posts on the forums advocating the use of higher viscosity oils in hot climates, say 10w-30 vs. 5w-30, or 10w-40 vs. 10w-30.

What I don't get(and correct me if I'm wrong), is that it seems to me that the temperature inside of an engine in operation and at operating temperatures will be pretty much independent of the outside temperature- that's what the cooling system is for, right?

In other words, it's not going to be any hotter inside a warmed up engine if it's 100 degrees outside or 30 degrees outside, because the thermostat will keep it in the right temperature range...
B

Thread '"Cool Climates" and Oil Viscosity - WTH'

I keep seeing people referring to the local climate as an indicator of whether an engine will survive on a thinner oil or not. Like saying a 20wt makes sense up North, but it wouldn't work in the desert.

Can someone please explain to me the logic of climate affecting oil temps to a SIGNIFICANT degree?

I live in Canada (Ottawa, Ontario), what most people would condider a "cool" climate relative to much of the world. It gets over 90F here in the summer. No MFR tells people to switch oil grades seasonally anymore...

...and the same model of car comes equipped with the same oil whether...
L

Thread 'Question about oil grades'

Quick question about oil viscosity specifications in cars. Are engines/cars designed and based around a specific viscosity of oil, and SHOULD run that oil, OR are oil specs only in relation to the environment/tempature/ style of driving that the engineers expect the engine to be used in, so you may use whatever reasonable oil viscosity you feel is fit. Always been curious about this, thanks
K

Thread 'BMW ambient temp/viscosity chart question'

For my 22 year old BMWs the owner's manual recommends 15w-40 for temps between 0F and 85F. On the single grade side of the chart they recommend SAE 30 for temps between 30F and 85F. 10w-40 is limited to ambient temps no greater than around 50 degrees. Why, when Havoline 10w-40 has higher viscosity numbers at 100C than straight Havoline 30 weight?
I'm asking mainly because I can get Havoline 10w-40 for free, and Castrol GTX 20w-50 which I've used for many years is getting rather dear. Free is a very good price.
M

Thread 'How does high ambient temperature affect oil ?'

I see posts from people from Las Vegas and elsewhere thinking they need a better oil at > 100F ambients. If a vehicle is operated under similar conditions (normal driving), how does ambient temperature become an issue if any engine cooling system generally maintains a stable engine operating temperature. I am asking what is the other variable in the equation.
R

Thread 'Curious - why thicker visc for summer versus...'

winter if the overall engine temp should be staying the same - irregardless of hot ambient temps?

My owners manual in 2 vehicles recommends different viscosities for different temps, and I have no problems following that. In fact, I prefer a thicker oil in the summer; however, I've noticed the BITOG board is split in this regard.

Some are opting for thicker visc, some say there's no difference in outside ambient temp versus overall engine temp.

So, which is it? Curious, personally.
S

Thread 'Higher viscosity in summer heat??'

I see alot of people post that they run a higher viscosity oil in the sumer months. Like 5w20 in winter then 5w30 or 10w30 in summer. I understand that the higher weight oil can provide better protection but isn't that because it is a bit thicker (more viscous) at operating temps? I guess what I'm asking is if a 5w20 might run a motor a smidge cooler compared to a 5w30? Or do I have this backwards? Seems like the less resistance the motor has on it the cooler it'd run. Wouldn't a more viscous oil be harder to cool down too? And shouldn't a motor run about the same temp in cold and hot...
P

Thread 'Does ambient air temp matter /that/ much for weight?'

Living in AZ, this summer I expect to see my daytime highs no less than 105F or so with a few 115F+'s thrown in here an there until well into October.

Now I traditionally have run M1 15-50 in my Toyota 1FZ-FE engine (~100k) and my Ford Probe 4cyl (~160k) during the summer months due to traditional logic of higher outside temp == higher viscosity.

Is this flawed thinking? The engine will operate roughly at the same temperature once warmed regardless of outside temp assuming my cooling systems are working fine.

That said, the manufacturer's both mention 5-30 as the recommended...
W

Thread 'Why do people run higher weight oil in summer?'

I have seen a lot of people recommend running a 5w30 instead of a 5w20 in summertime. As far as I know, the engine operating temp isn't going to be higher in the summer. If the manual says 5w20 is fine year round, why mess with it?
A

Thread 'Increasing oil weight for hotter climate?'

Hi all, first post here. Far from an oil expert, and hoping to expand my knowledge a bit.

I ride a late model Kawasaki Z1000 with about 40k on the clock. I've recently moved, and average temps are significantly hotter here. I've exclusively run the bike on Mobil 1 Racing 4t 10W-40 so far, but according to the official owner's manual, it is recommended to use either a 10W-50 or 20W-50 when the atmospheric temp exceeds 104° F (pretty common here).

I've always been the kind of person to simply follow manufacturer recommendations on oil weights, but I've also believed (just a gut...
 
mark pruett said:
But the part I can't quite square is the thinking that somehow a engine that specifies using 30 weight (or 20, 40, etc...) and has a say... 203 degree thermostat is going to somehow require heavier oil when the ambient temp is high outside.

What am I missing, if anything?
Click to expand...
Our last diesel pickup would drop oil pressure climbing mountain grades in the summer, towing our camper, about 17,500# gross. Hot coolant coming back from the radiator wasn't pulling enough heat from the oil via the oil cooler. It's a problem because the piston jets had check valves on them an would shut off somewhere below 28 psi. I'd generally downshift at around 35 psi and back out a bit. All of this typically happening before the fan clutch kicked in.

In cool weather, the radiator was more effective which kept cool water supplied to the oil cooler, and oil temperatures under control.

So there you have it, a concern relevant for oil viscosity in the heat. With a thinner oil, I could've lost piston cooling, which would've wasted the motor pretty quickly. With a thicker oil, more margin could've been had.
 
kschachn said:
Here are a few previous threads which may be of interest:

P

Thread 'Correct Viscosities Vs Ambient Temperatures'

I live in JHB,
temperatures here in winter go down to 5 in early mornings but warm up to average of 15-20degrees C.
Summer it averages from 15-20 in the mornings and gets sometimes hot maybe 25-35 degrees C.

I'm fully aware of thinner oils are far better,having better starting abilities and running smoother,with better fuel economy.
wink.gif


I'm currently running RL 5w40, its winter here, no problems but suggestions concerning viscosity ALL year round....
frown.gif
D

Thread 'Thicker oil for hotter ambient temp, Why?'

It's common for manufacturers to recommend thicker oil for higher ambient temperature. But if the coolant temperature gauge says the bike isn't running hotter, why different oil? Does the engine have hotter operating conditions in some way not indicated by coolant temperature? Or in the case of my air/oil cooled BMW temperature of whatever the dash indicator is measuring.

I wonder because temps have been high here lately (38+ C, 100+ F). And for the CRF1000L I just changed the oil on, the only recommended grade is 10W30. Yet on the africa twin forums some owner report that their local...
dlundblad

Thread 'Oil Weight and Ambient Temperatures'

I asked this before, but didnt get a straight answer.

Whats the point of running a thicker running weight in extreme heat? We see here that (some) Australians and folks in the Middle East like a 50 or 60 weight oil. Wouldn't the radiator keep oil temperature somewhat in check and prevent any oil related failures? I would also think an oil cooler would be a standard option for vehicles in these regions. We also see engines that spec a much thicker weight in Europe and the other mentioned regions while the identical US version will take a 20 or 30 weight oil. (It has been mentioned here...
4

Thread 'Does ambient air temperature matter or not for Oil'

I am greatly confused about one main thing: Air and climate temperature, vs grade of oil selected for a car. Please let me explain.

In almost any pre-2001 car manual (and some after that) i see, i see charts of temperature vs grades listed for the engine. Most charts list 10W-40 from around 10 or 20 degrees, those graphic arrow charts (the lowest ambient temperature i saw listed acceptable to 10W-40 was "4 degrees," i forget in which manual) - up to 100+. Then 10W-30 is listed as 0 or -5 on up, with 5W-30 going to approx. -20, on up. This is reason number one for the confusion.

Reason...
G

Thread 'Grades for high ambient temperature locations'

Living in the greater Phoenix, Arizona area we have winter temperatures down to -4C/25F and summer temperatures above 43C/110F. There are days when it gets above 46C/115F.

I'm convinced manufacturer's recommended grades of 5W20 or 5W30 are not appropriate at higher ambient temperatures. I suspect that 10W40 or 10W50 is appropriate.

I'm a long, long time Mobil 1 user but the only oil that fits that spec is a high mileage formulation ... in the US. In Europe, however, they produce a 10W60 for BMW-M cars!

I know Mobil 1 is available in 0W40 but the 0W winter rating is overkill in the...
L

Thread 'Viscosity and climate'

Im wondering why people tend to use a "thicker" or higher viscosity oil in hotter climate. The thermostat keeps the engine about the same operating temp whether in hotter or colder climates right?

To me, it is more of a decision of how much protection do you need vs effeciency savings...any thoughts?
S

Thread 'Viscosity vs. ambient temperature'

I live in southern California, where for most of the year it doesn't get below 60 degrees or so. However, in the winter, we do have some mornings where the temps are below freezing, evidenced by frost on the grass and windshields.

The recommended oil for my '97 F-150 is 5w-30, which is what I'm using now. The only thing that bothers me about this grade of motor oil is that in a lot of the UOA's, it seems to shear down to a 20-wt. in 5000 miles or less. My truck has over 200,000 miles on the clock, so I think a 30-wt. is probably a good choice.

I've read Motor Oil 101, and while I know...
O

Thread 'Viscosity Grade recommendation for Death Valley'

Death Valley is about 130F. 🔥

For my 0/5W-20 passenger cars, I prefer using a good 40 weight synthetic or at a minimum a very stout 30 unless I'm driving downhill.

Last 2 trips to Nevada, I used 40 and iirc, it wasn't even hotter than 95F.

What do you use or recommend?
  • Like
P

Thread 'Viscosity comparison - is it important?'

So here is my question:

If you look at oil comparisons there is a viscosity at 40 and 100 listed in the specs. There are several calculators around that will extrapolate that out for any operating temperature. The combination of the 40 and 100 can make a large difference in viscosity at operating temp if it is not 100. So here is my question - how important is the viscosity at operating temps (affect performance?), and what would be the normal operating temps for cars (100?), boats (80?), air cooled engined (no guess?).

Should I plot out the OEM recommended oil for temps, and verify my...
edhackett

Thread 'Interesting Temperature-Viscosity Chart'

Here's the recommended viscosity grades for given ambient temperatures for my 1991 BMW K100. This is a 1000cc, water cooled, inline four cylinder, with a four quart sump capacity.

Notice the complete lack of trust in multi-viscosity oils. They allow for it to shear back to its base viscosity. This is assuming mineral base and service grades SE, SF, SG.

SAE 20: -10 to 20C
SAE 30: 0 to 30C
SAE 40: 20 to 50C

SAE 10W30: -30 to 0C
SAE 10W40: -30 to 5C
SAE 10W50: -30 to 10C
SAE 15W40: -20 to 20C
SAE 15W50: -20 to 30C
SAE 20W40: -10 to 30C
SAE 20W50: -10 to 40C

Ed
M

Thread 'Ambient temperature vs. engine temperature'

I've read many posts on the forums advocating the use of higher viscosity oils in hot climates, say 10w-30 vs. 5w-30, or 10w-40 vs. 10w-30.

What I don't get(and correct me if I'm wrong), is that it seems to me that the temperature inside of an engine in operation and at operating temperatures will be pretty much independent of the outside temperature- that's what the cooling system is for, right?

In other words, it's not going to be any hotter inside a warmed up engine if it's 100 degrees outside or 30 degrees outside, because the thermostat will keep it in the right temperature range...
B

Thread '"Cool Climates" and Oil Viscosity - WTH'

I keep seeing people referring to the local climate as an indicator of whether an engine will survive on a thinner oil or not. Like saying a 20wt makes sense up North, but it wouldn't work in the desert.

Can someone please explain to me the logic of climate affecting oil temps to a SIGNIFICANT degree?

I live in Canada (Ottawa, Ontario), what most people would condider a "cool" climate relative to much of the world. It gets over 90F here in the summer. No MFR tells people to switch oil grades seasonally anymore...

...and the same model of car comes equipped with the same oil whether...
L

Thread 'Question about oil grades'

Quick question about oil viscosity specifications in cars. Are engines/cars designed and based around a specific viscosity of oil, and SHOULD run that oil, OR are oil specs only in relation to the environment/tempature/ style of driving that the engineers expect the engine to be used in, so you may use whatever reasonable oil viscosity you feel is fit. Always been curious about this, thanks
K

Thread 'BMW ambient temp/viscosity chart question'

For my 22 year old BMWs the owner's manual recommends 15w-40 for temps between 0F and 85F. On the single grade side of the chart they recommend SAE 30 for temps between 30F and 85F. 10w-40 is limited to ambient temps no greater than around 50 degrees. Why, when Havoline 10w-40 has higher viscosity numbers at 100C than straight Havoline 30 weight?
I'm asking mainly because I can get Havoline 10w-40 for free, and Castrol GTX 20w-50 which I've used for many years is getting rather dear. Free is a very good price.
M

Thread 'How does high ambient temperature affect oil ?'

I see posts from people from Las Vegas and elsewhere thinking they need a better oil at > 100F ambients. If a vehicle is operated under similar conditions (normal driving), how does ambient temperature become an issue if any engine cooling system generally maintains a stable engine operating temperature. I am asking what is the other variable in the equation.
R

Thread 'Curious - why thicker visc for summer versus...'

winter if the overall engine temp should be staying the same - irregardless of hot ambient temps?

My owners manual in 2 vehicles recommends different viscosities for different temps, and I have no problems following that. In fact, I prefer a thicker oil in the summer; however, I've noticed the BITOG board is split in this regard.

Some are opting for thicker visc, some say there's no difference in outside ambient temp versus overall engine temp.

So, which is it? Curious, personally.
S

Thread 'Higher viscosity in summer heat??'

I see alot of people post that they run a higher viscosity oil in the sumer months. Like 5w20 in winter then 5w30 or 10w30 in summer. I understand that the higher weight oil can provide better protection but isn't that because it is a bit thicker (more viscous) at operating temps? I guess what I'm asking is if a 5w20 might run a motor a smidge cooler compared to a 5w30? Or do I have this backwards? Seems like the less resistance the motor has on it the cooler it'd run. Wouldn't a more viscous oil be harder to cool down too? And shouldn't a motor run about the same temp in cold and hot...
P

Thread 'Does ambient air temp matter /that/ much for weight?'

Living in AZ, this summer I expect to see my daytime highs no less than 105F or so with a few 115F+'s thrown in here an there until well into October.

Now I traditionally have run M1 15-50 in my Toyota 1FZ-FE engine (~100k) and my Ford Probe 4cyl (~160k) during the summer months due to traditional logic of higher outside temp == higher viscosity.

Is this flawed thinking? The engine will operate roughly at the same temperature once warmed regardless of outside temp assuming my cooling systems are working fine.

That said, the manufacturer's both mention 5-30 as the recommended...
W

Thread 'Why do people run higher weight oil in summer?'

I have seen a lot of people recommend running a 5w30 instead of a 5w20 in summertime. As far as I know, the engine operating temp isn't going to be higher in the summer. If the manual says 5w20 is fine year round, why mess with it?
A

Thread 'Increasing oil weight for hotter climate?'

Hi all, first post here. Far from an oil expert, and hoping to expand my knowledge a bit.

I ride a late model Kawasaki Z1000 with about 40k on the clock. I've recently moved, and average temps are significantly hotter here. I've exclusively run the bike on Mobil 1 Racing 4t 10W-40 so far, but according to the official owner's manual, it is recommended to use either a 10W-50 or 20W-50 when the atmospheric temp exceeds 104° F (pretty common here).

I've always been the kind of person to simply follow manufacturer recommendations on oil weights, but I've also believed (just a gut...
Click to expand...
how do you find so many threads? incredible.
 
Unlike coolant, oil temperature often isn't regulated at all. Some engines have oil-coolant heat exchangers , but they don't regulate temperature perfectly, and maximum oil temperatures might still vary by over 10°C seasonally.
 
Engines in automobiles are only partially cooled by the cooling system. A percentage of the heat radiates from the external surfaces of the engine including from the oil pan. As ambient temperatures increase, the heat transfer from the engine surface is less efficient, so sump temperatures can increase even though the coolant temps are constant.
 
mark pruett said:
Having been around here for nearly two decades, I've read more comments talking about how people run higher viscosities when it's hotter outside, and vice-versa. This makes a sort of intuitive sense, as oils, even multigrade ones, thin out as temperatures increase. And that phenomenon explains why we'd want lower "W" numbers on multigrades as well- that indicates thinner oils at start-up temps, which are considerably cooler than within a warmed up engine.

But the part I can't quite square is the thinking that somehow a engine that specifies using 30 weight (or 20, 40, etc...) and has a say... 203 degree thermostat is going to somehow require heavier oil when the ambient temp is high outside.

The reason this doesn't really make sense to me is because the difference between "comfortable" and "super-hot" is like 25-35 degrees Fahrenheit, and is *still* 100 degrees F below the operating temp of the vehicle. The assumption is that the cooling system is so feeble that driving it in say... 105F temps is going to overwhelm the cooling system and necessitate higher viscosity to offset those temps. This would be the same if we're talking bearings, cams, etc.... the cooling system would have to be nearly ineffective for the ambient temp to really matter, provided the oil is in the right spec, as it's trying to keep everything right around 203, and the *internal* heat generated by combustion, in the bearings, etc... is what needs to be shed. The only place ambient temp comes into it would be in being able to shed the heat that the cooling system is moving from inside the engine to outside, and that's affected by the ambient temp. Even then, the main thing is going to be the internal heat generation rate, not so much the ambient temp, provided it's not something absurd like 120F outside.

What am I missing, if anything?
Click to expand...
In your example a 203 degree water thermostat doesn't control the oil temperature nor does it control the water temperature. It just opens at 203 to allow full passage of coolant past the thermostat housing.

The oil temperature is influenced by a lot of factors and just because water temperature is X doesn't mean oil temp is also X. That doesn't mean the cooling system is "nearly ineffective" because the radiator or air oil coolers can only exchange with the ambient temperature. It's a thermodynamics equation. Hotter ambient temperature means less offset to "trade" between air and fluid.

On a 70 degree day. My water temps can be 200, meanwhile oil temperature is 260.
On a 90 degree day. My water temps can be 210, meanwhile oil temperature is 280.

What am I missing, if anything?
Click to expand...
Data. Since data like the oil pressure and oil temperature will inform any viscosity changes that are needed due to seasonal ambient temperature changes.
 
I consider it mostly the myth of personal exceptionalism. It goes both ways. "I am brave to start my car at minus five degrees Farenheit in my elite exclusive hunting cabin up north." "I have chosen a house in Phoenix, Florida where only hardened souls like myself can handle the 105'F heat with an 85' dewpoint."

Then, because the person struggles, they assume the car struggles too. It's mechanical empathy taken too far. I'm all for mechanical empathy-- I've seen people beating on machines-- but engines don't need it exclusively due to temperatures.

Every once in a while BITOG gets the nugget of someone wanting an oil that will survive their wife driving. 😁
 
eljefino said:
I consider it mostly the myth of personal exceptionalism. It goes both ways. "I am brave to start my car at minus five degrees Farenheit in my elite exclusive hunting cabin up north." "I have chosen a house in Phoenix, Florida where only hardened souls like myself can handle the 105'F heat with an 85' dewpoint."

Then, because the person struggles, they assume the car struggles too. It's mechanical empathy taken too far. I'm all for mechanical empathy-- I've seen people beating on machines-- but engines don't need it exclusively due to temperatures.

Every once in a while BITOG gets the nugget of someone wanting an oil that will survive their wife driving. 😁
Click to expand...
That's gotta be some kinda oil! 😂

Wife driving can be a lot like mother in law thermostat adjusting... 100% off or 100% on all the time.
 
interesting facts + opinions + i will add another, real synthetic groups IV + V oils react differently to temperatures than others!! there are a LOT of variables in driving habits as well, one size does NOT fit all
 
johnmyster said:
So there you have it, a concern relevant for oil viscosity in the heat. With a thinner oil, I could've lost piston cooling, which would've wasted the motor pretty quickly. With a thicker oil, more margin could've been had.
Click to expand...
Right, but would that have been any different if it had been 40F cooler in the fall or winter? I somehow doubt it- your engine was kicking out way more heat than the cooling system could handle and that's why your temps were rising, not the outside temp. You needed better cooling, not necessarily heavier oil. Tomato-tomato, but it's not a function of weather when you come down to it.
 
CarlB said:
On a 70 degree day. My water temps can be 200, meanwhile oil temperature is 260.
On a 90 degree day. My water temps can be 210, meanwhile oil temperature is 280.
Click to expand...

I don't see that in my experience. On a 30 degree day, my water temps are around 203, and on a 105 degree day, they're exactly the same.
In your example a 203 degree water thermostat doesn't control the oil temperature nor does it control the water temperature. It just opens at 203 to allow full passage of coolant past the thermostat housing.
Click to expand...

It's not an all-open/all-closed valve that just opens up at the set temp. Instead, it's a valve that's controlled by something called a 'wax thermostatic element', meaning that there's a container of a specific sort of wax in there with a piston, and that wax expands and contracts a specific way at specific temperatures.

So when the car's cold, that wax is solid, and the valve's closed. As the car heats up, it expands, opening the valve accordingly with the temp. And it does this continuously as the car is in operation. The whole thing is engineered to keep the temperature at the set-point, say 203. So if the incoming cooling water is above that, it opens up a little bit more because the wax expands a little bit more. If it is below that, it shrinks the wax a little, restricting the flow a little and bringing it back up to temp.

And I seriously doubt automakers engineer their cooling systems such that they're wide open at the operating temp. That's just idiotic- far better to give some cushion in there by setting the thermostat up such that it's got some wiggle room to open up further than that.

That's why I don't see the temps fluctuate- that thermostat's doing its job and keeping the water temp where it's supposed to, independent of outside temp.
 
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My minivan has an oil temp gauge and I can tell you, the outside ambient temperature definitely has an effect on the oil temperature.
In anything below 90F, my oil temp will run about 185-190f when going down the highway or being stuck in stop and go.

Once the outside temp is around 100f, my heavy traffic oil temps can reach 210-220f range. Once I get going it will go down to 190F range.

Having said that, the difference in my vehicle doesn’t warrant a heavier oil.
 
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mark pruett said:
Right, but would that have been any different if it had been 40F cooler in the fall or winter? I somehow doubt it- your engine was kicking out way more heat than the cooling system could handle and that's why your temps were rising, not the outside temp. You needed better cooling, not necessarily heavier oil. Tomato-tomato, but it's not a function of weather when you come down to it.
Click to expand...
Actually, it's 100% a function of weather. The water returning from the radiator is a function of ambient temperature, airflow across the radiator, and at some point, engine load. Cooler ambient would have meant better heat rejection at the radiator.

mark pruett said:
I don't see that in my experience. On a 30 degree day, my water temps are around 203, and on a 105 degree day, they're exactly the same.


It's not an all-open/all-closed valve that just opens up at the set temp. Instead, it's a valve that's controlled by something called a 'wax thermostatic element', meaning that there's a container of a specific sort of wax in there with a piston, and that wax expands and contracts a specific way at specific temperatures.

So when the car's cold, that wax is solid, and the valve's closed. As the car heats up, it expands, opening the valve accordingly with the temp. And it does this continuously as the car is in operation. The whole thing is engineered to keep the temperature at the set-point, say 203. So if the incoming cooling water is above that, it opens up a little bit more because the wax expands a little bit more. If it is below that, it shrinks the wax a little, restricting the flow a little and bringing it back up to temp.

And I seriously doubt automakers engineer their cooling systems such that they're wide open at the operating temp. That's just idiotic- far better to give some cushion in there by setting the thermostat up such that it's got some wiggle room to open up further than that.

That's why I don't see the temps fluctuate- that thermostat's doing its job and keeping the water temp where it's supposed to, independent of outside temp.
Click to expand...

The theremostat (and likely also your ECT probe) are on the water outlet of the engine. The thermostat is functioning to either send water to the radiator or through a bypass loop, back to the input of the engine. It's adjusting the input water temperature to keep the output the same. Under high load it recruits more cold (radiator) water to keep the ECT output the same. Under no load or during warmup, bypass flow dominates.

You are correct, thermostats open gradually across a range of temperature. As output is hotter, more flow is diverted from bypass to the radiator. So engine coolant output temperature is nearly constant. (This does not mean oil temperatures are constant. Quite the opposite actually.)

That is, until the radiator begins to saturate and warm water is coming back. This is when you will see temperatures rise, increasing heat rejection from the radiator and perhaps recruiting some radiator fan flow.
 
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ripcord said:
Engines in automobiles are only partially cooled by the cooling system. A percentage of the heat radiates from the external surfaces of the engine including from the oil pan. As ambient temperatures increase, the heat transfer from the engine surface is less efficient, so sump temperatures can increase even though the coolant temps are constant.
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While I don't doubt that radiative cooling from the pan is significant, I'm not so sure it's affected by ambient temp nearly so much as airflow would be(conduction). And I'd think if it was useful or necessary to cool the oil pan like that, oil pans would have *real* cooling fins, not just shallow pretty grooves cut into them. Like a computer heat sink or something.
 
mark pruett said:
While I don't doubt that radiative cooling from the pan is significant, I'm not so sure it's affected by ambient temp nearly so much as airflow would be(conduction). And I'd think if it was useful or necessary to cool the oil pan like that, oil pans would have *real* cooling fins, not just shallow pretty grooves cut into them. Like a computer heat sink or something.
Click to expand...
That would be convection, not conduction. I do remember a discussion on this in some automotive engineering class and if I recall correctly it was primarily convection cooling rather than radiation. But it depends of course on airflow, temperature differential and pan geometry (as you note).
 
johnmyster said:
Actually, it's 100% a function of weather. The water returning from the radiator is a function of ambient temperature, airflow across the radiator, and at some point, engine load.
Click to expand...

What I'm getting at is that 20 or even 50 degrees Fahrenheit isn't going to affect your oil temp that much if your cooling system is functioning properly. Yes, the oil temp may vary a little b
kschachn said:
That would be convection, not conduction. I do remember a discussion on this in some automotive engineering class and if I recall correctly it was primarily convection cooling rather than radiation. But it depends of course on airflow, temperature differential and pan geometry (as you note).
Click to expand...
I wasn't sure; doesn't convection have to do with the actual convective motion of the fluid/gas? As in, it heats up, rises away from the heat source, and then cools and sinks?

Either way it's not radiation, but the action of the air over the pan that transfers most of the heat. And oil pans aren't really designed to transfer much heat.
 
mark pruett said:
I wasn't sure; doesn't convection have to do with the actual convective motion of the fluid/gas? As in, it heats up, rises away from the heat source, and then cools and sinks?

Either way it's not radiation, but the action of the air over the pan that transfers most of the heat. And oil pans aren't really designed to transfer much heat.
Click to expand...
Convection can be either forced or natural. Forced is more effective at moving heat. In both cases the heat is transferred from the solid object to a liquid media that then moves across the surface.

Even so, convection involves conduction, because the heat had to be conducted through/along the oil pan, etc.

Conduction can also involve fluids, but the fluid would be static, so heat has to spread through the fluid media.

Radiation is different. It occurs even across a vacuum.

Undergrad thermodynamics was one week conduction, one week radiation. They are easily understood. The remainder of the semester was convection, most of it natural. It's the most difficult to understand/characterize which is why your wife always burns/undercooks dinner in the oven...which adds confusion to the topic. In modern kitchens we call them convection ovens. Really they're all convection ovens. The ones with a fan are forced, the ones without a fan are natural.
 
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