Viscosity and climate

[lockguy]

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?

 

[AlienBug]

I do believe you have offered a false choice. Your protection v/ efficiency argument assumes that heavier oils protect better. That is an assertion that never has been proven.

I think the people that use heavier oil in warm weather or switch viscosity between winter and summer are clinging to habits that were outdated 30 years ago.

Oh well. In a few years I'll be the dinosaur and the kids driving fusion aircars will be ridiculing me. Such is life.

 

[OVERKILL]

Originally Posted By: AlienBug
I do believe you have offered a false choice. Your protection v/ efficiency argument assumes that heavier oils protect better. That is an assertion that never has been proven.

I think the people that use heavier oil in warm weather or switch viscosity between winter and summer are clinging to habits that were outdated 30 years ago.

Oh well. In a few years I'll be the dinosaur and the kids driving fusion aircars will be ridiculing me. Such is life.


The requirement for a heavier lubricant to provide the necessarily protection correlates with oil temperature which usually correlates with power density.

This is why transport trucks spec 15w-40 instead of 5w-20. And why pretty much all the Euro marques spec an oil with an HTHS >=3.5cP for their higher power density applications. This is why Ford spec's 5w-50 for the BOSS 302 and GT500, why Ferrari spec's a 10w-60....etc.

Remember, viscosity is not a static measure. It scales directly with temperature, so if your oil temperatures are too high, a thinner lubricant like a 5w-20 may simply not provide enough film strength. On the other hand, in a car that calls for 10w-60 and gets putted around town, the oil will never get to a temperature that its additional thickness is beneficial, let alone necessary.

 

[kr_bitog]

Originally Posted By: lockguy
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?


The different viscosity for 40 and 50 weight compared to 30 weight is not much when the engine coolant hit 100C, I believe this thicker is needed on country with hot weather and ridiculously traffic jam and the aircon is at full blast. May be this scenario is less relevant in North America, but in country like Brazil, China, Indonesia, Thailand this is daily scenario and it worsen by only low quality based engine oil available makes the thicker oil is necessary to fight the fuel dilution and ensure longevity the engine.

With cheap gas in those, the engine longevity priority is just purely outweight the efficiency saving, that in those scenario the fuel saving is negligible due to very little viscosity difference

 

[Ducman]

Originally Posted By: lockguy
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?


Hi Lockguy,

As already mentioned, a lot depends upon the application, design and power density of the engine.

You need to condider that within the engine there are some parts (for example valve train components in engines with flat tappet cams) that endure highly elevated point loading stresses and subsequently experience higher temperatures which are not reflected in oil temp gauges, or even remotely corelate to coolant temps as shown on the temp gauge.
These temps will seriously thin out a thicker oil in the immediate area, leaving only boundary layer lubrication to protect the parts as a last line of defence.
Boundary layer lubrication is only 1 part of the different phases of lubrication.

Some current owners manuals provide clear guidelines as to what oil viscosity you should run within given ambient temperature ranges for engines, transmission and diffs.

Also for example, Amsoil on their website recommend 5w-30 oil for the engine in my car, but have a caveat written in to cover any application when ambient temps over 32 F occur, where they recommend a 10w-30 oil.
There are currently no exceptions in their recommendations for this engine as utilized in my car.
The engine has a hydraulic roller camshaft, and in my car there is no oil cooler or oil/coolant heat exchanger.

Cheers

 

[HerrStig]

Spare us ANOTHER "heavier/lighter" rant. I know what my owner's manuals say.

 

[fdcg27]

Originally Posted By: OVERKILL
Originally Posted By: AlienBug
I do believe you have offered a false choice. Your protection v/ efficiency argument assumes that heavier oils protect better. That is an assertion that never has been proven.

I think the people that use heavier oil in warm weather or switch viscosity between winter and summer are clinging to habits that were outdated 30 years ago.

Oh well. In a few years I'll be the dinosaur and the kids driving fusion aircars will be ridiculing me. Such is life.


The requirement for a heavier lubricant to provide the necessarily protection correlates with oil temperature which usually correlates with power density.

This is why transport trucks spec 15w-40 instead of 5w-20. And why pretty much all the Euro marques spec an oil with an HTHS >=3.5cP for their higher power density applications. This is why Ford spec's 5w-50 for the BOSS 302 and GT500, why Ferrari spec's a 10w-60....etc.

Remember, viscosity is not a static measure. It scales directly with temperature, so if your oil temperatures are too high, a thinner lubricant like a 5w-20 may simply not provide enough film strength. On the other hand, in a car that calls for 10w-60 and gets putted around town, the oil will never get to a temperature that its additional thickness is beneficial, let alone necessary.


By "power density", do you mean specific output?
If so, specific output in a stock normally aspirated engine doesn't get much higher than that of the two liter Honda S2000, and Honda specs it for any garden variety API 10W-30.
No exotic specs or heavier grade required.

 

[Eddie]

Coolant temperature stays constant because of a thermostat, but, oil temperature varies as the engine load and outside temperature. I think this is the question asked? Ed

 

[gfh77665]

Its a matter of optimizing the visc choice. Down here on the Gulf Coast, a "0" or "5" does little good. 10-30 is a great choice here, its all we need and fits our climate great. In ND, MN, Canada, etc, you bet a "0" or "5" is needed. No doubt about it.

The other choices won't destroy anything, its just better to use what fits best, thats all.

 

[Cristobal]

It feels better to me, so in summer I still use the higher viscosities.

 

[Shannow]

Originally Posted By: fdcg27
Originally Posted By: OVERKILL
Originally Posted By: AlienBug
I do believe you have offered a false choice. Your protection v/ efficiency argument assumes that heavier oils protect better. That is an assertion that never has been proven.

I think the people that use heavier oil in warm weather or switch viscosity between winter and summer are clinging to habits that were outdated 30 years ago.

Oh well. In a few years I'll be the dinosaur and the kids driving fusion aircars will be ridiculing me. Such is life.


The requirement for a heavier lubricant to provide the necessarily protection correlates with oil temperature which usually correlates with power density.

This is why transport trucks spec 15w-40 instead of 5w-20. And why pretty much all the Euro marques spec an oil with an HTHS >=3.5cP for their higher power density applications. This is why Ford spec's 5w-50 for the BOSS 302 and GT500, why Ferrari spec's a 10w-60....etc.

Remember, viscosity is not a static measure. It scales directly with temperature, so if your oil temperatures are too high, a thinner lubricant like a 5w-20 may simply not provide enough film strength. On the other hand, in a car that calls for 10w-60 and gets putted around town, the oil will never get to a temperature that its additional thickness is beneficial, let alone necessary.


By "power density", do you mean specific output?
If so, specific output in a stock normally aspirated engine doesn't get much higher than that of the two liter Honda S2000, and Honda specs it for any garden variety API 10W-30.
No exotic specs or heavier grade required.


And Honda builds their bearing projected surface areas, and clearances to meet that requirement...it's both sides of the same coin.

The oft quoted 50s recommendations, the engines had comparatively massive bearing areas, and low BMEP.

 

[lockguy]

Originally Posted By: HerrStig
Spare us ANOTHER "heavier/lighter" rant. I know what my owner's manuals say.


go pound sand, this is a forum for constructive conversation, nobody is ranting on anything. These kind folks are kind enough to answer my questions. If you know what you manual says, why are you here?

 

[lockguy]

Originally Posted By: Ducman
Originally Posted By: lockguy
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?


Hi Lockguy,

As already mentioned, a lot depends upon the application, design and power density of the engine.

You need to condider that within the engine there are some parts (for example valve train components in engines with flat tappet cams) that endure highly elevated point loading stresses and subsequently experience higher temperatures which are not reflected in oil temp gauges, or even remotely corelate to coolant temps as shown on the temp gauge.
These temps will seriously thin out a thicker oil in the immediate area, leaving only boundary layer lubrication to protect the parts as a last line of defence.
Boundary layer lubrication is only 1 part of the different phases of lubrication.

Some current owners manuals provide clear guidelines as to what oil viscosity you should run within given ambient temperature ranges for engines, transmission and diffs.

Also for example, Amsoil on their website recommend 5w-30 oil for the engine in my car, but have a caveat written in to cover any application when ambient temps over 32 F occur, where they recommend a 10w-30 oil.
There are currently no exceptions in their recommendations for this engine as utilized in my car.
The engine has a hydraulic roller camshaft, and in my car there is no oil cooler or oil/coolant heat exchanger.

Cheers


thanks for the intuitive post. It does make sense that at some parts of the engine might getter hotter due to stresses on that part. But....if for instance, a particular car was sold throughout the US, texas, louisiana etc, and it says on the cap, 5w-20, don't you think the engineers took that into account? Most owners manuals do not specify different weight oil depending on climate, i know i have not seen one.

if the thermostat keeps the coolant at 200 F, the engineers are anticipating that the engine is going to be a certain temperature. Im not sure that whether its 50F or 110F outside, the coolant is going to stay roughly the same 200F, therefore the engine will be within normal operating temperatures. I would think that the temperature of those particular parts will be roughly porportionate to the temperature of rest of the engine and/or the coolant. so if the coolant temp is consistant, so is the oil, so is the engine.

 

[OVERKILL]

Originally Posted By: fdcg27
Originally Posted By: OVERKILL
Originally Posted By: AlienBug
I do believe you have offered a false choice. Your protection v/ efficiency argument assumes that heavier oils protect better. That is an assertion that never has been proven.

I think the people that use heavier oil in warm weather or switch viscosity between winter and summer are clinging to habits that were outdated 30 years ago.

Oh well. In a few years I'll be the dinosaur and the kids driving fusion aircars will be ridiculing me. Such is life.


The requirement for a heavier lubricant to provide the necessarily protection correlates with oil temperature which usually correlates with power density.

This is why transport trucks spec 15w-40 instead of 5w-20. And why pretty much all the Euro marques spec an oil with an HTHS >=3.5cP for their higher power density applications. This is why Ford spec's 5w-50 for the BOSS 302 and GT500, why Ferrari spec's a 10w-60....etc.

Remember, viscosity is not a static measure. It scales directly with temperature, so if your oil temperatures are too high, a thinner lubricant like a 5w-20 may simply not provide enough film strength. On the other hand, in a car that calls for 10w-60 and gets putted around town, the oil will never get to a temperature that its additional thickness is beneficial, let alone necessary.


By "power density", do you mean specific output?
If so, specific output in a stock normally aspirated engine doesn't get much higher than that of the two liter Honda S2000, and Honda specs it for any garden variety API 10W-30.
No exotic specs or heavier grade required.


Power density is exactly what it sounds like, how much power is derived from a given displacement.

However, the displacement itself is relevant because a 2L engine (your S2K example) making 200HP and a 5L engine making 500HP aren't going to heat the oil equally. The 5L engine is going to generate more heat because it generates more power.

However what Honda DIDN'T do was spec 5w-20 for the S2000

(or even 5w-30!) So even they were concerned about shear (as we know a 10w-30 will be more shear stable by virtue of having much less polymer in it than a 5w-30 in general) and what the lowest viscosity the engine would actually see in operation was

 

[crazyoildude]

+1

 

[lockguy]

Originally Posted By: Eddie
Coolant temperature stays constant because of a thermostat, but, oil temperature varies as the engine load and outside temperature. I think this is the question asked? Ed


Yes,that is the question. Good point you bring up. Thermal conductivity is fairly linear. I don't know but I would think that as the temperature of the engine went above the temperature of the coolant, the coolant would conduct that heat out the radiator and keep the engine temp in check. When ambient temperature is higher though, the temperature differential between the radiator and the outside temperature is less. The rate of heat dissipation will slow.

I guess the question is not if, but how much variation in engine temp and how much that variation effects viscosity.

 

[OVERKILL]

Originally Posted By: lockguy
Originally Posted By: Eddie
Coolant temperature stays constant because of a thermostat, but, oil temperature varies as the engine load and outside temperature. I think this is the question asked? Ed


Yes,that is the question. Good point you bring up. Thermal conductivity is fairly linear. I don't know but I would think that as the temperature of the engine went above the temperature of the coolant, the coolant would conduct that heat out the radiator and keep the engine temp in check. When ambient temperature is higher though, the temperature differential between the radiator and the outside temperature is less. The rate of heat dissipation will slow.

I guess the question is not if, but how much variation in engine temp and how much that variation effects viscosity.


That's why radiators are sized according to their application and why vehicles have thermostats. Coolant temperature is pretty well regulated regardless of ambient. Eddie's point is more in respect to OIL temperature, which, in many vehicles is NOT regulated through a cooling device like an oil cooler.

In many cases, while coolant temp is within its normal range, depending on ambient and load, oil temperatures can be much, MUCH higher.

And this is a bit of an extension of my earlier posts, but that is why in applications with engines that have the capability to heat the oil significantly, they are oft fitted with oil coolers. Usually thermostatically controlled ones at that.

 

[Ducman]

Originally Posted By: lockguy
Originally Posted By: Ducman
Originally Posted By: lockguy
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?


Hi Lockguy,

As already mentioned, a lot depends upon the application, design and power density of the engine.

You need to condider that within the engine there are some parts (for example valve train components in engines with flat tappet cams) that endure highly elevated point loading stresses and subsequently experience higher temperatures which are not reflected in oil temp gauges, or even remotely corelate to coolant temps as shown on the temp gauge.
These temps will seriously thin out a thicker oil in the immediate area, leaving only boundary layer lubrication to protect the parts as a last line of defence.
Boundary layer lubrication is only 1 part of the different phases of lubrication.

Some current owners manuals provide clear guidelines as to what oil viscosity you should run within given ambient temperature ranges for engines, transmission and diffs.

Also for example, Amsoil on their website recommend 5w-30 oil for the engine in my car, but have a caveat written in to cover any application when ambient temps over 32 F occur, where they recommend a 10w-30 oil.
There are currently no exceptions in their recommendations for this engine as utilized in my car.
The engine has a hydraulic roller camshaft, and in my car there is no oil cooler or oil/coolant heat exchanger.

Cheers


thanks for the intuitive post. It does make sense that at some parts of the engine might getter hotter due to stresses on that part. But....if for instance, a particular car was sold throughout the US, texas, louisiana etc, and it says on the cap, 5w-20, don't you think the engineers took that into account? Most owners manuals do not specify different weight oil depending on climate, i know i have not seen one.

if the thermostat keeps the coolant at 200 F, the engineers are anticipating that the engine is going to be a certain temperature. Im not sure that whether its 50F or 110F outside, the coolant is going to stay roughly the same 200F, therefore the engine will be within normal operating temperatures. I would think that the temperature of those particular parts will be roughly porportionate to the temperature of rest of the engine and/or the coolant. so if the coolant temp is consistant, so is the oil, so is the engine.







You make good points.
I have 5 vehicles in my garage.
1 has clear advise in the owners manual that has temp based variations for oil viscosity from one end of the vehicle to the other.
2 have a ridgidly fixed recommendation of 10w-30 and 20w-50 respectively.
The other 2 vehicles (2010 and 2012 models) have a strong recommendation of 15w-50, which is up from their previous strong recommendation of 10w-40 that dates from about 2005-2006 when they started to increase/extend the service intervals by 50%. They do provide room to move in the owners manual regarding oil viscosity that is temp based which varies between a 10w-40 and 20w-50. Do you notice the trend?

Yes i totally agree that the engineers know a thing or 2 and provide specifications accordingly.
However, in recent times i think there would be plenty of engineers that would be tearing their hair out because their employers are directing them to work with thinner oils to help meet government enforced CAFE fuel consumption regulations.
Thank god for the development of thinner but higher quality oils that can protect adequately which is driven by the car manufacturers. If these modern oils weren't so good we probably wouldn't be having this discussion.

Enter modern engine designs that are not as hard on the oils, with more than 2 valves per cylinder, actuated by multiple over head cams and lighter valve springs.
Also as an example, there is one car manufacturer in the USA that in 2012 was strictly specing a 5w-30 oil. For 2013 they spec a 5w-20 for the exact same engine.

I guess the point i'm trying to make here is that if it weren't for the govt regulations, and market forces we wouldn't be looking to progressively thinner oils to pursue better fuel economy going forward.

Honestly, the coolant temp is a very poor indicator of oil temp.
That's why a racing car typicaly has a separate oil temp gauge.
Obviously in a typical daily driver the difference between oil/water temp is not as great as in a high performance/race car that is being driven on a track.
I refer you to the writings of Dr Haas regarding viscosity requirements, which can be accessed here on BITOG.

Ferrari for example, currently spec a 5w-40 for a street driven car, but put it on a track for some fun and they say to only use a full synthetic 10w-60 (nothing else).
See, same engine in the same car used in different applications require different viscosity/quality oil.

Cheers

 

[Ducman]

Originally Posted By: lockguy
Originally Posted By: Eddie
Coolant temperature stays constant because of a thermostat, but, oil temperature varies as the engine load and outside temperature. I think this is the question asked? Ed


Yes,that is the question. Good point you bring up. Thermal conductivity is fairly linear. I don't know but I would think that as the temperature of the engine went above the temperature of the coolant, the coolant would conduct that heat out the radiator and keep the engine temp in check. When ambient temperature is higher though, the temperature differential between the radiator and the outside temperature is less. The rate of heat dissipation will slow.

I guess the question is not if, but how much variation in engine temp and how much that variation effects viscosity.


This is correct, only up to a point. Again it depends upon the application and ambient temps.
I forgot to add earlier that it has been known for race teams to put a thin oil in for doing limited qualifying laps because they needed every horsepower they could get to achieve the best starting position, but they change it over to the thicker oil for the actual race.

 

[Shannow]

Oil isn't a passive partner in the heat exchange of an engine.

The frictional losses that are available to provide power and mileage are a direct reflection of the fact that the engine carries out work against the oil.

Unlike coolant, which for a large part of it's process is preventing metal components from exceeding allowable temperatures from the fire taking place in the Combustion Chamber, the oil is being actively worked against, which increases it's temperature.

Bearings, the temperature rise can be 10-40F...consider that some of the oil will splash against the cylinder wall, some pool in the head and drain back, there is still a fair amount that makes it straight from the bearing(s) back to the sump "uncooled"...ever seen a finned sump ? what is that telling you ? where's the control mechanism there ? what does ambient do to oil temperature when that's factored in ?

Which allows the bulk oil temperature to exceed the thermostatically controlled coolant temperature, and under extreme conditions by a significant margin.

If you can pick up 5hp in a racing engine with an oil change, consider putting 2KW of heaters in a couple of gallons of oil, and how you could make a stable oil temperature through a couple of square feet of tin sump...

That being said, saving 5hp through friction reduction does not mean that the racing engine is lasting longer, just that the trade-off between (friction robbing) full hydrodynamic lubrication and mixed/boundary conditions of least friction have been explored and accepted.