U think we will ever see a 0W20 which.....?

[river_rat]

Originally Posted By: CATERHAM
The WolfsHead KV100 spec' is undoubtedly a typo'.
It is likely 8.6cSt.
The reason is the minimum HTHS vis' for a 20wt oil is 2.6cP and you can't make a 20wt oil with a KV100 spec' much below 8.0cSt and still retain a HTHS vis of 2.6cP.

That makes sense. But that typo has been around quite a while. Makes me wonder.

 

[CATERHAM]

Originally Posted By: dparm
I said excluding those three.

So you did!
Consider the elaboration a freeby.

 

[AEHaas]

One of the BITOG members ran a 10 grade oil in an old jeep that worked well without mishap.

aehaas

 

[river_rat]

Originally Posted By: AEHaas
One of the BITOG members ran a 10 grade oil in an old jeep that worked well without mishap.

aehaas


Makes me think the bearing loads are over-built (or perhaps I should say under-loaded) enough that the film strength is sufficient to keep the metal apart even in a very thin oil.

The SAE paper I have on bearing wear with low HT/HS viscosity oils (1.4 cSt or less) shows a curve of increased wear at these very low HT/HS viscosities, but that curve is also a line of best fit on a scatter chart with only about a dozen data points (if I recall correctly). The text states to the effect that bearing failure tended to be an all or nothing affair, with the failures that did occur being at the very low end of viscosity--as opposed to a steady and predictable increase in wear as the HT/HS viscosity dropped.

I am not ready to go below an initial HT/HS of 2.6 that SAE mandates for a licensed XW-20, but an engine can be engineered to run on much below this if they choose to do so.

 

[CATERHAM]

Originally Posted By: AEHaas
One of the BITOG members ran a 10 grade oil in an old jeep that worked well without mishap.
aehaas

We've had a couple including the late Gary Allan but his "experimental oil" still had a HTHSV of 2.6cP so it wasn't a true 10wt oil.

The lightest SM/SN oil on the market today is the Toyota Brand 0W-20. In reality it is better thought of a a 0W-15 oil since it shears about 10% (based on oil pressure) immediately in service and then stabilizes. Since this is spec' oil for most Toyota and Lexus models now, Toyota certainly has confidence in running such a light oil.

I've seen a number of tests running 5wt (HTHSV 1.7cP) oil without issue. The key is oil temperature. If you keep the bulk oil temp's at 80C, the low end of normal, it really is not any different than running the Toyota 0W-20 oil at 100C.

 

[river_rat]

Originally Posted By: CATERHAM
...The key is oil temperature. If you keep the bulk oil temp's at 80C, the low end of normal, it really is not any different than running the Toyota 0W-20 oil at 100C.

True, and I suspect my Toyota runs to the cool side in oil temps. 6.1 quart sump, and I had difficulty getting the oil temp above 180F when I was doing PSID test across my oil filter.