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Re: Variable Oil Pressure ... can it be done?


Galant VR-4 org Post #: 901983 posted 05/26/10 11:27 AM     Remind Me!  Send Private Message   Edit Post      
It almost certainly does. However unless someone sticks an oil pressure gauge on a motor and takes a reading we will never know for sure. The only other possibility I can think of is that the 4g61 comes with a much larger oil relief valve.

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Galant VR-4 org Post #: 902089 posted 05/26/10 06:36 PM     Remind Me!  Send Private Message   Edit Post      
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.

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Edited by Dialcaliper (05/26/10 06:56 PM)

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I'm an idiot...

Galant VR-4 org Post #: 902098 posted 05/26/10 07:05 PM     Remind Me!  Send Private Message   Edit Post      
I saw an aftermarket oil distribution block for the head posted above, reminds me I've seen some variations between those on 4G engines...

-Joshua Adventure Driven Design
1991 Galant VR-4
1999 Montero "Goldi-Locker"

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Galant VR-4 org Post #: 902531 posted 05/28/10 03:45 AM     Remind Me!  Send Private Message   Edit Post   
Quoting cheekychimp:

The issue is this, with the Balance Shafts in the engine removed people are seeing 100 psi on cold starts and up to 100 psi at WOT (7500 rpms). So whilst I think your idea might work to prevent cold start pressure surges, it will probably be worse for high rpms. I think I am going to have to port the oil filter housing relief valve and then experiment with different restrictors.

I see you have been reading my thread lol

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