Thick vs thin debate...

Messages
7,310
Location
FL, USA
Yes, beating a dead horse here. I’m not looking for an argument but am curious. It is often cited here that engines can handle running a wide viscosity range of oils, which I agree with. But for some reason 0w20 (or thin oils in general) are viewed as the devil and shouldn’t be used in engines that previously specified a higher viscosity.

Example: the VW / Audi 1.4 TSI and 2.0 TSI. They previously ran 502.00 (30-40 grade) but now run 508.00 (0w20). So again, if engines can handle operating under such a large viscosity range (think thick oil when cold and thin when hot, which is quite the spread in CST measurement, and they DO handle that viscosity difference well)...why would it be detrimental to that engine to drop the grade down to a 20 from a 30? That is only a few CST thinner at operating temp (12 cst for 30 and 7ish cst for 20). That seems negligible IMO

Honest question.
 
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Messages
12,973
Location
North Carolina
..why would it be detrimental to that engine to drop the grade down to a 20 from a 30? That is only a few CST thinner at operating temp (12 cst for 30 and 7ish cst for 20). That seems negligible IMO

Honest question.
Don't know if its detrimental, but i don't see an advantage for the engine to do it.

Especially now, with DI where the oil can get diluted and thin from the fuel alone.
 
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gathermewool

Site Donor
Messages
8,915
Location
New England
Yes, beating a dead horse here. I’m not looking for an argument but am curious. It is often cited here that engines can handle running a wide viscosity range of oils, which I agree with. But for some reason 0w20 (or thin oils in general) are viewed as the devil and shouldn’t be used in engines that previously specified a higher viscosity.

Example: the VW / Audi 1.4 TSI and 2.0 TSI. They previously ran 502.00 (30-40 grade) but now run 508.00 (0w20). So again, if engines can handle operating under such a large viscosity range (think thick oil when cold and thin when hot, which is quite the spread in CST measurement, and they DO handle that viscosity difference well)...why would it be detrimental to that engine to drop the grade down to a 20 from a 30? That is only a few CST thinner at operating temp (12 cst for 30 and 7ish cst for 20). That seems negligible IMO

Honest question.

Almost half the viscosity seems negligible to you?
 
Messages
27,234
Location
PNW
Yes, beating a dead horse here. I’m not looking for an argument but am curious. It is often cited here that engines can handle running a wide viscosity range of oils, which I agree with. But for some reason 0w20 (or thin oils in general) are viewed as the devil and shouldn’t be used in engines that previously specified a higher viscosity.

Example: the VW / Audi 1.4 TSI and 2.0 TSI. They previously ran 502.00 (30-40 grade) but now run 508.00 (0w20). So again, if engines can handle operating under such a large viscosity range (think thick oil when cold and thin when hot, which is quite the spread in CST measurement, and they DO handle that viscosity difference well)...why would it be detrimental to that engine to drop the grade down to a 20 from a 30? That is only a few CST thinner at operating temp (12 cst for 30 and 7ish cst for 20). That seems negligible IMO

Honest question.
Depends on where you live and how you drive the car. Since you're in FL, I'd stick with xW-30.
 

OVERKILL

$100 Site Donor 2021
Messages
45,842
Location
Ontario, Canada
Yes, beating a dead horse here. I’m not looking for an argument but am curious. It is often cited here that engines can handle running a wide viscosity range of oils, which I agree with. But for some reason 0w20 (or thin oils in general) are viewed as the devil and shouldn’t be used in engines that previously specified a higher viscosity.

Example: the VW / Audi 1.4 TSI and 2.0 TSI. They previously ran 502.00 (30-40 grade) but now run 508.00 (0w20). So again, if engines can handle operating under such a large viscosity range (think thick oil when cold and thin when hot, which is quite the spread in CST measurement, and they DO handle that viscosity difference well)...why would it be detrimental to that engine to drop the grade down to a 20 from a 30? That is only a few CST thinner at operating temp (12 cst for 30 and 7ish cst for 20). That seems negligible IMO

Honest question.

Quite simply:
- Engines are INCREDIBLY tolerant of going UP in viscosity. You'll not risk damage running 5w-50 for example in an engine that spec's 5w-20.
- Engines are NOT incredibly tolerant of going DOWN in viscosity. There's a point where you will exceed the hydrodynamic capacity of the lubricant under high temp/high shear conditions and when that happens, best case, you lose some bearing material, worst case, you spin the bearing, it locks to the journal, the rod comes off the piston and it exits the side of the block.

This is why manufacturer specs, particularly European ones, spec a minimum HTHS viscosity, that's the minimum viscosity that they deem sufficient under the worst case scenario to protect the rod bearings.

This is also why Honda when they started chasing even thinner oils went and widened the journals, as a wider bearing will have a higher load carrying capacity, which offsets the reduction in capacity from going to the thinner lube.

Back in the day they used to spec a wide range of viscosities that went right down to 5w-20 and gave specific temperature ranges these lubes were appropriate for as well as disclaimers about not operating in higher temperatures, avoiding highway speed...etc. Obviously, that's beyond the ability for most drivers nowadays. Here's an old BMW one:
1611018431050.png


You'll note 5w-20 wasn't suitable for ambient above 0C and an ILSAC 5w-30 or 10w-30 above 10C. This is because viscosity of course has a relationship with temperature. And there was of course still the risk of bearing damage if those grades were used and oil temp was driven up by extremely spirited driving, though without a oil/coolant heat exchanger it was likely the oil temp stayed well below coolant temp.
 
Messages
3,014
Quite simply:
- Engines are INCREDIBLY tolerant of going UP in viscosity. You'll not risk damage running 5w-50 for example in an engine that spec's 5w-20.
- Engines are NOT incredibly tolerant of going DOWN in viscosity. There's a point where you will exceed the hydrodynamic capacity of the lubricant under high temp/high shear conditions and when that happens, best case, you lose some bearing material, worst case, you spin the bearing, it locks to the journal, the rod comes off the piston and it exits the side of the block.

This is why manufacturer specs, particularly European ones, spec a minimum HTHS viscosity, that's the minimum viscosity that they deem sufficient under the worst case scenario to protect the rod bearings.

This is also why Honda when they started chasing even thinner oils went and widened the journals, as a wider bearing will have a higher load carrying capacity, which offsets the reduction in capacity from going to the thinner lube.

Back in the day they used to spec a wide range of viscosities that went right down to 5w-20 and gave specific temperature ranges these lubes were appropriate for as well as disclaimers about not operating in higher temperatures, avoiding highway speed...etc. Obviously, that's beyond the ability for most drivers nowadays. Here's an old BMW one:
View attachment 41319

You'll note 5w-20 wasn't suitable for ambient above 0C and an ILSAC 5w-30 or 10w-30 above 10C. This is because viscosity of course has a relationship with temperature. And there was of course still the risk of bearing damage if those grades were used and oil temp was driven up by extremely spirited driving, though without a oil/coolant heat exchanger it was likely the oil temp stayed well below coolant temp.

Excellent post.
 
Messages
1,777
Location
South Carolina
I run 5w-20 in an engine that's spec'd for 5w/10w-30. However, it's a dragstrip only car, that runs for <3 minutes at a time, and the oil never exceeds 180*F. If I was planning to drive this engine on the street, it would have a 5w-30 in it.

There's nothing wrong with going up in viscosity a grade or two. You'll have some viscous losses in the bearings and the rings but not enough to really notice.
 
Messages
9,294
Location
Virginia
Exactly right Biscut...

You know who was called Biscuit ??

William "The Refrigerator" Perry....

Nickname given to him by the Chicago Bears Dan Hampton who said William was only 1 Biscuit shy of 350 pounds....
:)
 

OVERKILL

$100 Site Donor 2021
Messages
45,842
Location
Ontario, Canada
10W-30 not to be used over 10C (50F) and 10W-40 not to be used over 20C (68F), yet 15W-40 is good anything over 30C (86F). Hummm, what are those Bemmer engineers thinking? How old is that chart and the associated oils?

I'm guessing it's pretty old, probably 90's. 15w-40 would of course have an HTHS >3.5cP just like the LL oils on the right side of the chart that share a much broader range. My copy of J300 from 1999 shows 0w-40, 5w-40 and 10w-40 with an HTHS lower limit of 2.9cP, so that's likely the driver, which makes sense. The only non-LL and non-OEM grade that could be counted on having an HTHS of 3.5cP or higher would be the 15w-40.
 
Messages
3,085
Location
GA.
Quite simply:
- Engines are INCREDIBLY tolerant of going UP in viscosity. You'll not risk damage running 5w-50 for example in an engine that spec's 5w-20.
- Engines are NOT incredibly tolerant of going DOWN in viscosity. There's a point where you will exceed the hydrodynamic capacity of the lubricant under high temp/high shear conditions and when that happens, best case, you lose some bearing material, worst case, you spin the bearing, it locks to the journal, the rod comes off the piston and it exits the side of the block.

This is why manufacturer specs, particularly European ones, spec a minimum HTHS viscosity, that's the minimum viscosity that they deem sufficient under the worst case scenario to protect the rod bearings.

This is also why Honda when they started chasing even thinner oils went and widened the journals, as a wider bearing will have a higher load carrying capacity, which offsets the reduction in capacity from going to the thinner lube.

Back in the day they used to spec a wide range of viscosities that went right down to 5w-20 and gave specific temperature ranges these lubes were appropriate for as well as disclaimers about not operating in higher temperatures, avoiding highway speed...etc. Obviously, that's beyond the ability for most drivers nowadays. Here's an old BMW one:
View attachment 41319

You'll note 5w-20 wasn't suitable for ambient above 0C and an ILSAC 5w-30 or 10w-30 above 10C. This is because viscosity of course has a relationship with temperature. And there was of course still the risk of bearing damage if those grades were used and oil temp was driven up by extremely spirited driving, though without a oil/coolant heat exchanger it was likely the oil temp stayed well below coolant temp.
*What is the likely minimum HTHS number to protect rod bearings ? Also , what is the likely safe upper ambient temperature for 5W20 ?
 
Messages
1,393
Location
Kennett Square, PA
Lol, not beating a dead horse, famous last words... and 40% difference in CST? I am a schoolteacher and didn’t get a raise this year because of Covid. Go ahead and send me that negligible 40% of your salary, haha.
Didn’t get a raise, huh? I’d say you did pretty well compared to so many people who lost jobs completely, shut down their business and buried loved ones. Guess you will have a bad summer vacation too with the travel restrictions.
 
Messages
2,209
Location
WA
Also , what is the likely safe upper ambient temperature for 5W20 ?

Temps inside the engine could be 400F+ in some parts and 230F+/- avg oil temps ... I wouldn't worry too much about ambient temp.

I have 2 cars that OM recommends 5W20 and 0W20 in US. One is a truck with over 10K towing capacity. The manufacturers don't think ambient temps in US will be an issue and neither do I except i prefer a thicker oil in general and especially if I'm towing.
 
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