AEHaas Writings

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The sticky above provides a link to AEHaas' treatise on the virtues of thin oils.

This is a very well reasoned and persuasive argument.

It would be great if someone could present an equally well reasoned explanation as to why the heavy oil camp likes heavy oils.

I would love to see this topic discussed in this way!

Any heavy oil types keen to provide a well reasoned and logically presented rebuttal or counter-point?
 
I too would like the see some comments on this topic. With not much more than some shade tree wrench turning to back me up I feel that a heavier oil will provide a cushioning effect to some degree for cam followers and timing chains and gears. Plain old water would work for an insert bearing given you provided enough pressure across the bearing suface to keep a fliud wedge on the loaded area.
 
I for one can't trust 5W-20 in a stop and go 50C weather with a/c running, just don't feel comfortable enough to do so. I know that my diff turns SAE 90 oil to water in that same situation.
 
There are engine architectures where very thin oils work just fine, and there are engine architectures where using very thin oils is not so fine.

For journal bearings, thin oils is a simple machining, precision fitting, and oil flow problem. And easily solved during any major change in engine internals/blocks/heads.

For valve and valve guides thin oil is probably just as good as thicker oils.

For cylinder walls, a thin oil is actually likely to be better than a thick oil (based on resent articles).

For engines that have overhead cams that directly actuate valves via a tapett, thin oils can only be used if the tapet has a large enough surface area (as does the cam lobe) and the valve springs are light enough. This may not be possible on high performance motorcycles or automotive engines that can spin over 7,000 RPMs.

For engines with cam-in-block designs, with roller followers and rollerized rockers, thins oils should work just fine.
 
Dr. Haas frequently mentions that his light oils are for his normal [20 min] short trips.
If racing full out for long periods, he would use a heavier oil.
 
From 105

In an earlier section I said that thicker oils are usually needed in racing situations but not necessarily. Remember that a major function of oil is to cool the inside of your engine. In ASTM D 4485 3.1.4: “Terminology: Engine oil- a liquid that reduces friction and wear between moving parts within an engine, and also serves as a coolant.” Since the oil with a viscosity of 10 cS at 212 F thins to a viscosity of 3 cS at 302 F we will get more flow. The pressure will go down some as well. This is OK as long as we have a minimum of pressure to move the oil.

This increased flow will result in increased cooling by the oil. This is a good thing. You would probably want more oil flow in these situations and you get it. The hotter oil thins and this increases flow. The higher flow works harder to separate the engine parts that are under very high stress. It all works out for the better. Higher revving engines need thinner oils. You do not necessarily need to go to a thicker oil while racing. Only experimentation will tell.

In the majority of cases only the manufacturer has time and resources for scientific experimentation, and even then probably only one brand of oil.
As an example
http://www.silkoleneoil.com/techtip6.htm
Am I recommending 0W/20 for high performance engines? Well, perhaps not! The
Pro S 5W/40, which is a 'proper' PAO/ESTER shear-stable synthetic, will look
after a powerful engine better than a heavier viscosity 'cave at the back'
conventional oil, and provide a useful few extra BHP. (On the other hand,
the 0W/20 was very thoroughly developed to give good anti-wear protection.
I think I was on 'Blend 6' before Kawasaki was happy with it!).

I am more confident using say a 5W40 if recommended than experimenting with a thin oil.
 
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