I would prefer to do away with the SAE J300 oil grades and grade them as CCS-HTHS.
Very true. Some mechanical problems like oil pressure loss can be caused by wear in engine bearings for example, from using an oil that was too thin. I prefer having a nice safety margin built in, instead of having "adequate protection."As far back as my memory can go, oil pressure loss is a sign of a mechanical problem.
@OVERKILL
Thanks for the info!
Just to make sure I understand this correctly, based on J300 table, 20W Min cSt can be between 5.6 and 9.299 (< 9.3). Is that true?
if true, 9.3 also happens to be borderline Max hot rating cSt for 20 and 30 grades (i.e. it could be a very thick 20 or a thin 30) ... is that why you are saying 20W hot rating might be 20 or 30?
Q2:
was the 9.3 under the Min and Max cSt columns of Widman table by design or just a coincidence? What's the story behind it if any?
A safety margin is not one ended. Too thick an oil, especially at higher RPM, may result in the worst type of wear within moving parts, cavitation. This is when chunks of metal are pulled off of the surfaces. If the oil is a little thin and the moving surfaces get close then the additive package comes into play to prevent or minimize any wear. Nothing can prevent cavitation if the fluid cannot keep up with the movement of parts.Very true. Some mechanical problems like oil pressure loss can be caused by wear in engine bearings for example, from using an oil that was too thin. I prefer having a nice safety margin built in, instead of having "adequate protection."
This true and there are always trade offs. My homework lead me to a 30 grade for my two Jeep applications. IMO it offers the best of both worlds, especially since they weren't specifically built for a 20 grade oil only, and the spec was more for CAFE credits than anything else.A safety margin is not one ended. Too thick an oil, especially at higher RPM, may result in the worst type of wear within moving parts, cavitation. This is when chunks of metal are pulled off of the surfaces. If the oil is a little thin and the moving surfaces get close then the additive package comes into play to prevent or minimize any wear. Nothing can prevent cavitation if the fluid cannot keep up with the movement of parts.
AEHaas
Very true. Some mechanical problems like oil pressure loss can be caused by wear in engine bearings for example, from using an oil that was too thin. I prefer having a nice safety margin built in, instead of having "adequate protection."
That's true regarding a catastrophic failure. Wear can also result in a catastrophic failure as well.As far as wear rates are concerned over a long period of time, yes. Sudden catastrophic bearings failures though are often the result of an issue with the crankshaft such as excessive torsional vibration or crank walk/warp. In such cases, you could have Nitro 70 in the bearings and it won't prevent a thing.
I could see that in Siberia, and I agree it would be a problem. But at my ambient temps it will never be a problem. Plus the fact that main and rod bearing clearences have not gotten smaller than when 5w30 was common use.A safety margin is not one ended. Too thick an oil, especially at higher RPM, may result in the worst type of wear within moving parts, cavitation. This is when chunks of metal are pulled off of the surfaces. If the oil is a little thin and the moving surfaces get close then the additive package comes into play to prevent or minimize any wear. Nothing can prevent cavitation if the fluid cannot keep up with the movement of parts.
AEHaas
Of all the papers and studies I've read on lubrication and tribology, cavitation between moving parts is never discussed ... why is that? Most cavitation concerns are at the PD oil pump. Anyone have some technical papers addressing cavitation between moving parts, like cam lobe and a valve follower or between piston/rings and a cylinder wall?A safety margin is not one ended. Too thick an oil, especially at higher RPM, may result in the worst type of wear within moving parts, cavitation. This is when chunks of metal are pulled off of the surfaces. If the oil is a little thin and the moving surfaces get close then the additive package comes into play to prevent or minimize any wear. Nothing can prevent cavitation if the fluid cannot keep up with the movement of parts.
AEHaas
Cavitation is generally written about wrt diesel cooling systems … pretty rare in lubricant fields … butOf all the papers and studies I've read on lubrication and tribology, cavitation between moving parts is never discussed ... why is that? Most cavitation concerns are at the PD oil pump. Anyone have some technical papers addressing cavitation between moving parts, like cam lobe and a valve follower or between piston/rings and a cylinder wall?
And besides, I highly doubt there is going to be any cavitation potential difference between 20 to 50 weight oils when they are at operating temperature. If there is cavitation due to oil being too thick, then every oil viscosity is going to have cavitation as it goes from a cold start to operating temperature, especially in very cold weather conditions.
Cold start up wear? The fuel mixture is richer. This affects the cylinder walls. Especially true with DI engines. My mazda had >5% fuel after 8 mile trips which is my wife's typical commute.If the thicker oil at the lower engine temperature has no ill effects then why is wear higher? If thicker oil lubricates better than thinner oil why is there more wear.
The answer cannot be that the engine parts are not fitting together well at start up. The oil lubricates or it doesn't.
AEHaas
How about some links to said papers, since you know all about them."Search,read,and study some of Shannow’s papers."
Search, read, and study some of Dr. Eric Schneider's papers who has performed most of the oil research for GM, as one example. There are numerous SAE papers on start up wear.
AEHaas
How about some links to said papers, since you know all about them.
It all depends on the specific design of the engine's oiling system, because the oil pressure delta per 1000 PRM increase is dependent on all kinds of things - ie, overall oiling system flow resistance and design, oil pump volumetric output and efficiency, oil viscosity & temperature, etc.Getting back to 10PSI/1000 RPM:
My comment - As long as the system pressure is 10 PSI for every 1,000 RPM then oil flow should be sufficient to keep the bearing wet in a properly working SI engine.