Any downsides to thicker oil?

[CATERHAM]

Originally Posted By: Jim Allen
Originally Posted By: CATERHAM
I believe the old oil axiom applies;
"the oil should be as thin as possible and just as thick as necessary".


Never heard that applied to oil, but the old Land Rover/Camel Trophy off-highway driving creedo that was pounded into us was:

"As slowly as possible, as fast as necessary."

I'm adapting the oil one to

"As thin as possible, as thick as necessary."

And I will use it shamelessly!


Jim, feel free to use it, I only wish I originated the phrase.
Some insightful tribologist I'm sure.

 

[CATERHAM]

Originally Posted By: Jim Allen
Originally Posted By: CATERHAM

When you switch to PU 5W-20 with it's HTHS vis of 2.7 cP, the actual operational viscosity should be noticeably lower. Since you have an oil pressure gauge in your truck I'd be interested to know how much your hot oil pressure drops at elevated rev's vrs the RLI; comparing at the same exact rpm.


That's an interesting ponderment. Will the oil pressure change noticeably with an increase in HTHS when the base 100C viscosity stays the same, or similar?


That's my experience with all the oils I've used including RL.
But it shouldn't come as a surprise since the HTHS vis is measured under pressure and the kinematic 100C vis spec' is not.
What I think throws a lot of people is the fact that the HTHS vis is determined at 150C and therefore they
assume incorrectly that it doesn't apply at more normal operating temps.

Bottom line, in determining how thick an oil is in terms of operational viscosity, at normal operating temps and up,the HTHS vis spec' trumps the less accurate 100C k'vis spec.

 

[StevieC]

 

[CATERHAM]

Originally Posted By: il_signore97
Originally Posted By: Jim Allen
Originally Posted By: CATERHAM

When you switch to PU 5W-20 with it's HTHS vis of 2.7 cP, the actual operational viscosity should be noticeably lower. Since you have an oil pressure gauge in your truck I'd be interested to know how much your hot oil pressure drops at elevated rev's vrs the RLI; comparing at the same exact rpm.


That's an interesting ponderment. Will the oil pressure change noticeably with an increase in HTHS when the base 100C viscosity stays the same, or similar?





If the oil pump is in bypass (which it most likely will be at or near redline), then no, there will be no noticeable difference in oil pressure as measured by the gauge. However, the engine will see a difference in flow between the two oils, but that difference cannot be measured easily.
Originally Posted By: il_signore97
Originally Posted By: Jim Allen
Originally Posted By: CATERHAM

When you switch to PU 5W-20 with it's HTHS vis of 2.7 cP, the actual operational viscosity should be noticeably lower. Since you have an oil pressure gauge in your truck I'd be interested to know how much your hot oil pressure drops at elevated rev's vrs the RLI; comparing at the same exact rpm.


That's an interesting ponderment. Will the oil pressure change noticeably with an increase in HTHS when the base 100C viscosity stays the same, or similar?



If the oil pump is in bypass (which it most likely will be at or near redline), then no, there will be no noticeable difference in oil pressure as measured by the gauge. However, the engine will see a difference in flow between the two oils, but that difference cannot be measured easily.


If your oil pump is in bypass at or near redline when the oil is at normal operating temps' you're running an oil that's too thick for your application.

I actually use my oil pressure gauge as variable redline of sorts during my warm up regimen. I will short shift the car at rev's below the point of bypass (90 psi in my Caterham) on my oil gauge. When cold in the summer that will translate into rev's of only 2,000 rpm with 20wt oil initially, but will rise quickly. In a couple of minutes I'll be able to shift at 3,500 rpm before bypass. It will take about 10 minutes before I can shift at 6,500 rpm and avoid bypass, that corresponds to oil temps of about 55C. It takes about 30 minutes for the oil to get up to 80C and that corresponds to oil pressure of 75 psi at 6,500 rpm. At 95C oil temps the oil pressure will have dropped to 65 psi at 6,500 rpm but I only see those temps' on the track.

 

[il_signore97]

Originally Posted By: CATERHAM
If your oil pump is in bypass at or near redline when the oil is at normal operating temps' you're running an oil that's too thick for your application.



Not necessarily. In my experience, I've seen engines that bypass below the redline while using the specified grade of oil after hours of driving (thus assuming normal operating oil temps). One example is my friend's GM 4.3L V6. It specifies 5W30 and he uses Amsoil 0W30 in it. After using it to tow a boat for 2 hours, the oil pressure will hit bypass (65 psi) at around 4,000 rpm. And those circumstances are the hottest possible oil temps that the engine will experience in its use.




Originally Posted By: CATERHAM
I actually use my oil pressure gauge as variable redline of sorts during my warm up regimen. I will short shift the car at rev's below the point of bypass (90 psi in my Caterham) on my oil gauge. When cold in the summer that will translate into rev's of only 2,000 rpm with 20wt oil initially, but will rise quickly. In a couple of minutes I'll be able to shift at 3,500 rpm before bypass. It will take about 10 minutes before I can shift at 6,500 rpm and avoid bypass, that corresponds to oil temps of about 55C. It takes about 30 minutes for the oil to get up to 80C and that corresponds to oil pressure of 75 psi at 6,500 rpm. At 95C oil temps the oil pressure will have dropped to 65 psi at 6,500 rpm but I only see those temps' on the track.



Funny that you mentioned this, because I do the same thing where an oil pressure gauge is available. Where not available, I use intuition to guess at an "imaginary" redline.



Sorry Stevie for all the O/T in your thread!!! It kind of just flowed from your initial question about thicker oil and such...

 

[StevieC]

It's all good... It's interesting... I actually asked Caterham a question but I think he missed it.

So what would be the best 5w20 with the highest HT-HT and I guess that would be my sweet-spot oil for my truck seeing as it likes the RLI 5w20?


Steve

 

[il_signore97]

Stevie,

He's busy responding to my posts! (It's a slow day at work as you can see - just don't tell my boss... lol)

If I had to guess without doing any research, I'd say RLI or Redline 5W20 would have to be the two with the highest HTHS vis. There could be others that I don't know of. RL's is 3.3 cP for their 5W20.

 

[StevieC]

That's what I was thinking... Re: HTHS

As for a slow day, yeah for me too and so I'm on BITOG... Not many times do I get a day like this!

Sun is shining, I have a good cup of coffee and internet in my car!

 

[CATERHAM]

That's a low bypass pressure of only 65 psi.
I think part of the reason the GM 4.3L is in bypass is because the Amsoil 0W-30 is a robust shear resistant oil with a HTHS vis of 3.4 cP. This is heavier than the spec' 5W-30. Even the M1 5W-30 ( 4718M ) with it's virgin HTHS vis of 3.09 cP will commonly shear a good 10% which would drop the vis down to at least 2.8 cP and still provide more than adequate viscosity I'm sure and lower oil pressure, likely below bypass.

 

[CATERHAM]

Originally Posted By: il_signore97
Stevie,

He's busy responding to my posts! (It's a slow day at work as you can see - just don't tell my boss... lol)

If I had to guess without doing any research, I'd say RLI or Redline 5W20 would have to be the two with the highest HTHS vis. There could be others that I don't know of. RL's is 3.3 cP for their 5W20.


I agree RL's 5W-20 has got to have the highest HTHS vis at 3.3 cP for a so-called 20wt. I'm familiar with this oil and not surprisingly (to me) my oil pressure is noticeably higher with it than M1 5W-30. I really consider the RL 5W-20 to be a mid-grade 30wt oil.

I don't consider a high HTHS vis relative to it's 100C vis spec'
to be good or bad. It's just what it is.
As far as I've determined it trumps the 100C vis spec as simply being a more accurate measure of an oils operational viscosity.

We don't know for sure what the HTHS vis is for RLI (Bill Garmier appears to be not as forthcoming with that info as RL is) but I suspect it is indeed lower than RL.

I've also got it on good authority that RL's 0W-20's HTHS vis is in reality higher than the 2.7 cP that RL claims; closer to 3.0 cP. That's still the lightest street oil of RL just not as light as they claim.

As far as "sweet spot" for a particular engine is concerned, their are so many variables in an oil, operational viscosity is just one of them although I think it's the the most important.

 

[StevieC]

Thanks... Might stick with it then.

 

[il_signore97]

Originally Posted By: CATERHAM

I don't consider a high HTHS vis relative to it's 100C vis spec'
to be good or bad. It's just what it is.
As far as I've determined it trumps the 100C vis spec as simply being a more accurate measure of an oils operational viscosity.



This has been a very interesting discussion so far. Thanks. (And I'm glad Stevie is okay with it! lol)

Anyway, I realize that a high HTHS vis. relative to a low 100C kin. vis. is just that, however, I do believe it has advantages. Redline 5W20 (used again for example) has a high HTHS of 3.3 cP, but a lower kin. vis. of 9.1 cSt. This is advantageous for things such as under piston sprayers, chain lubrication, flow (throughput) through galleries, etc. Although you claim the HTHS vis is much more accurate at determining operational characteristics of an oil, and I fully agree with you 100%, the kin. viscosity at 100C is still the viscosity of the oil under no load and under no shear (such as flowing through a camshaft gallery).

Thus, I see this as an advantage. More flow through the low pressure areas of an engine, and higher viscosity (as determined by HTHS) in bearing journals.

 

[CATERHAM]

The reason I believe you can ignore the 100C k'vis spec' is that when an engine is up to temperature (say 100C) the difference in viscosity between a 15 cSt oil and a 11 cSt oil is negligible in terms of unpressurized flow. Particularly when compared to lower temps like 0C or even 40C when the oil is many orders of magnitude thicker.

 

[river_rat]

Originally Posted By: StevieC
The only time I go against this rule is the 5w20 spec I usually use a 5w30...

I've been doing that too lately. I think Probably don't go up or down more than one weight from spec, nor less than a 20, unless you have an old oil burner...then maybe just use an HM oil.

 

[JAG]

Originally Posted By: CATERHAM
The reason I believe you can ignore the 100C k'vis spec' is that when an engine is up to temperature (say 100C) the difference in viscosity between a 15 cSt oil and a 11 cSt oil is negligible in terms of unpressurized flow. Particularly when compared to lower temps like 0C or even 40C when the oil is many orders of magnitude thicker.

That's approximately a 27% KV difference...100*(15-11)/15 which is large. When there are very low shear rates that translates to roughly the same 27% difference in flow rate. But I don't claim to know how much that matters to the engine at the high temps associated with those viscosities.

 

[Steve S]

Originally Posted By: Jim Allen
Originally Posted By: CATERHAM
I believe the old oil axiom applies;
"the oil should be as thin as possible and just as thick as necessary".


Never heard that applied to oil, but the old Land Rover/Camel Trophy off-highway driving creedo that was pounded into us was:

"As slowly as possible, as fast as necessary."

I'm adapting the oil one to

"As thin as possible, as thick as necessary."

And I will use it shamelessly!

 

[CATERHAM]

That's my thinking. Under pressure 27% is significant, otherwise the viscosities are too low.
If you had a jar of 15 cSt oil and a jar of 11 cSt oil each measured at room temperature and shook them both, I bet they would both appear to have the consistency of kerosene to the naked eye.

 

[Jim Allen]

Has anyone seen any oil pressure comparisons for oils of a similar kinetic viscosity but differing HTHS?

 

[CourierDriver]

I have never figured out how oil feels

 

[CATERHAM]

Originally Posted By: Jim Allen
Has anyone seen any oil pressure comparisons for oils of a similar kinetic viscosity but differing HTHS?


Jim, there's a project for you and thanks for the interest.

To be accurate you'll need a finely calibrated pressure gauge and oil temp' gauge. The test vehicle of course must operate with it's oil pressure at operating temp's that is below the oil pump bypass level.
Comparing any oil to one of RL's 5W-XX or heavier oils is a good place to start for a most extreme case.