posted 05/26/10 06:36 PM
Someone might also point out that the factory oil is either 10W30 or 5W30. Most people seeing pressure problems are running at least 10W40, or more likely, 20W50 or thicker oil (Like anyone foolish enough to run straight SAE 50 "race" oil in an engine not designed for it). An oil that is too thick cannot properly "wet" and stick to the surface it is supposed to protect, it also cannot flow as well through small gaps. In short, tighter main and rod bearing clearances require thinner oil.
Quite honestly, if you are still having over-pressure problems after the engine warms up, you are simply using oil that is too thick for a) the clearances in your engine and b) your local climate.
Also, there is a huge variation in actual viscosity between oil brands and types that carry the same "SAE" Weight. It's the same story as with tire diameter, width and treadwear. Look around at some oil spec sheets, and you'll see that (for example) some 10W40 oils have higher true viscosity at certain temperatures than other 20W50 oils.
Just because the oil is thicker does not mean it protects "better" if it is producing extremely high oil pressures. If your engine is not running hot enough to thin 20W50 oil out to produce normal operating pressures, you don't need to be running it, especially with modern high end synthetics, which have come a long way.
I'd also like to point out that while porting the filter housing can fix pressure problems, it's also a sign that oil thickness is working doubly against you - not only does higher pressure mean you are getting less oil flow to the moving parts in the engine (think of fuel pump outputs at high pressure), the oil relief opening even further means a larger fraction of the pump flow is dumping back into the pan.
The easiest way to alleviate pressure problems is switch to a lighter oil. If the problem is only when the engine is cold and thinner oil ends up with lower pressures at operating temperatures, a synthetic oil with more viscosity modifiers (0W-XX or 5W-XX oil) will help to reduce the pressures.
1269/2000 Summit White
Edited by Dialcaliper (05/26/10 06:56 PM)
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