Redline 5w30 - Turbo diesel usage

[BobFout]

Originally Posted By: CATERHAM
Bob I hate to tell you this but you can't compare the KV100 spec's of two widely different oil chemistries without making an adjustment.
The two viscosity spec's to consider are HTHS and the VI.
The 0W-40 has a very much higher 197 VI vs only 162 for the 5W-30 and a somewhat higher HTHSV. The net result of his is that
RL 5W-30 will be heavier than RL 0W-40 at all temp's below about 75C. At room temperature it will be about 25% heavier and more than 50% heavier at 0C. That relative difference will increase as the temp's drop below freezing.

If you wanted to improve the starting performance of the RL 0W-40 you would have been better off simply blending in some RL 0W-30 to produce whatever lower HTHSV you want. The blend will reduce the oil's VI but the reduction in the HTHSV more than compensates for this.


Same oil chemistry for both RL 0w40 and RL 5w30.

Do you disagree with the Widman chart for these?

 

[CATERHAM]

No they don't have the same chemistry. The 0W-40 uses a fare amount of VIIs and the base oils used are lighter. The 5W-30 contains no VIIs whatsoever, hence the very low KV100 spec relative to it's HTHSV; about the highest of any motor oil available.

You do know that the HTHSV trumps the KV100 spec' that I wrote about in the following thread?:
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2276304&page=1

If you want to use a kinematic viscosity calculator you'll have to either raise the viscosity of the 5W-30 or lower that of the 0W-40 for comparative purposes. Since the 5W-30's HTHSV is 5% lower than that of the 0W-40 use a 14.3 vs the 15.1 for the 0W-40 and a 92.1 KV40 value for the 5W-30. These values will retain the 5W-30's 162 VI.
Plug those figures into the calculator and you'll have a better idea of how the oils compare to each other.

 

[BobFout]

Originally Posted By: CATERHAM
No they don't have the same chemistry. The 0W-40 uses a fare amount of VIIs and the base oils used are lighter. The 5W-30 contains no VIIs whatsoever, hence the very low KV100 spec relative to it's HTHSV; about the highest of any motor oil available.

You do know that the HTHSV trumps the KV100 spec' that I wrote about in the following thread?:
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2276304&page=1

If you want to use a kinematic viscosity calculator you'll have to either raise the viscosity of the 5W-30 or lower that of the 0W-40 for comparative purposes. Since the 5W-30's HTHSV is 5% lower than that of the 0W-40 use a 14.3 vs the 15.1 for the 0W-40 and a 92.1 KV40 value for the 5W-30. These values will retain the 5W-30's 162 VI.
Plug those figures into the calculator and you'll have a better idea of how the oils compare to each other.



How does HTHS trump KV in those areas that do not experience high temp / high shear conditions.... not all areas of an engine are.

 

[CATERHAM]

HTHSV is a measure of an oils film strength.
About the only area in a typical IC engine that the kinematic method of measuring viscosity relates to would be the oil draining under the force of gravity back into the sump, of course nothing is being lubricated when that happens.

 

[BobFout]

Originally Posted By: CATERHAM
HTHSV is a measure of an oils film strength.
About the only area in a typical IC engine that the kinematic method of measuring viscosity relates to would be the oil draining under the force of gravity back into the sump, of course nothing is being lubricated when that happens.


And those areas that are high temp and low shear? Or low temp and high shear?

We talk on and on about how thinner oils flow better providing some benefits. HTHS certainly isn't flow

 

[CATERHAM]

Bob I think you're over thinking this.

HTHS is a method of measuring viscosity under conditions similar to those in an operating engine at 150C, consiquently oil under pressure (stress) is factored in, unlike the simply kinematic method.
As a result it doesn't matter what an oil's chemistry and VII level is, it's resultant HTHSV is an accurate measure that will stand on it's own. A HTHSV 3.5cP oil has the same operational viscosity as any other 3.5cP oil regardless of it's chemistry, a 2.6cP oil has the same operational viscosity as any other 2.6cP oil and so on. For any HTHSV you will have a range of possible KV100 values, but if you want to know how thick or thin the oil is at operating temperature compared to another oil it's the HTHSV you should look at.

This all assumes one thing and that is that the oil's you're comparing have the same viscosity index. Two oil's with the same HTHSV and the same VI will have the same operation viscosity at all temp's down at least to 0C and likely much lower. If one oil has a higher VI then it will become progressively lighter (relatively speaking) as the temp's drop. A VI difference of 15 or less won't have much impact as the temp's drop from 150C to 100C and even as far as 70C for light oils, since the change in viscosity is quite linear at those temp's, but the viscosity difference will be more pronounced as the temp's continue to drop.
When you get into large VI differences in the 20, 30 and higher range then the higher VI oil will be noticeably lighter even at temp's as high as 100C.

The bottom line is, in comparing the operational viscosities of different oils at temp's above freezing, you need know only the HTHSV and the VI, nothing else matters.

 

[2cool]

Caterham,
I thank you for the time and trouble you spend to explain these things in an accessible fashion.