Oil Cooler Bypass Valve- Cause of low oil pressure when car is warm?

[2Mitsus]

edit- DO THIS MOD AT YOUR OWN RISK (OBVIOUSLY)!! READ THE WHOLE THREAD BEFORE YOU MAKE A DECISION!!

This applies to turbo models only- as the service manual states this is only on the turbo models.

There's a picture of it in the service manual- chassis- section 11-40 #6 in the diagram (oil pan & oil pump removal & installation). For those without a service manual, it looks like a bolt going into the oil filter housing assembly.

There have been many threads regarding low oil pressure when warm and reasons behind low oil pressure, such as failing oil pump, bearing clearances & weak relief spring, however I have not seen this mentioned not even once as a possible reason. And people have replaced pumps, checked bearing clearances & found to be within spec, shimmed springs, fixed leaks, & changed their oil & filter, with very little or no improvement whatsoever.

The logic behind me suspecting this valve is simple- when oil heats up it breaks down. If the oil cooler bypass-valve is stuck in the position where oil is not going through the oil cooler, it's going to get pretty damn hot. Causing the viscosity to break down causing you to lose pressure.

I seriously doubt this is the one bulletproof part that the factory engineers installed on our cars.

Discussion? Anyone test/replace a faulty valve and see any noticeable improvement? I for one am going to call my dealer and order one of these to see for myself what happens to oil pressure when warm/hot.

[doctorstupid]

first, i wasn't even aware the oil cooler was on a valved system. good to know.

second, your oil has to be REALLY hot for the viscosity to decrease. like 300*F plus. under "normal" driving conditions you would be hard pressed to actually get your oil that hot. but if you're at WOT constantly, i'm sure you could do it inside of 20 minutes.

[ViperGTS2002]

I can see that happening if you're pushing the car hard. I didn't know the cooler was valved either . Another thing some people overlook is keeping the cooler clean. Every spring it would be a good idea to hit it with some degreaser and hose it out, just to clean any buildup off the fins. This will also help spot any leaks in the cooler itself. Having it located behind the IC isn't the best for airflow, especially if your intercooler fins are as beat up as mine

[2Mitsus]

I think we may be hitting 300* a bit easier than you're implying.
Consider this-
to test the valve, you have to:
a) measure the dimension that the valve moves with "normal" temperature and humidity
b) measure the dimension the valve moves, when dipped in 212*F oil.

I would assume that the engineers designed the valve to fully open at 212*F, based on the conclusion that it is fairly easy for the engine oil to reach 212 degrees without the valve fully open.

I don't think they would have it designed to open once the temps reach 300- it's supposed to prevent the oil from reaching those temps.

The valve is costing me $28- and is currently being ordered from the dealer (probably will arrive next Wednesday). In the meantime, if I can find the right size plug for the hole that is now there since the valve is removed, I'll try running with no valve in place to see if there are any changes. It's been about 100 degrees F every day lately, so I don't see any negative consequences of temporarily removing the valve.

ViperGTS2002- I'm not sure hosing out the oil cooler is such a great idea. You really don't want water to get mixed with your oil. Rinsing/soaking it in gasoline or having it professionally boiled out would be a better idea, in my opinion.

[ViperGTS2002]

Originally Posted by 2Mitsus

ViperGTS2002- I'm not sure hosing out the oil cooler is such a great idea. You really don't want water to get mixed with your oil. Rinsing/soaking it in gasoline or having it professionally boiled out would be a better idea, in my opinion.

I didn't mean the INSIDE, I meant the outside. Unless you've got a leak, or you're using a high-pressure spray, I can't see you mixing water into the oil path at all.

[mikes2nd]

agreed, i have been reading forever about people shimming the relief spring...

and here since i never looked it up, thought it was for the whole oil system.

its not, that spring is for the oil cooler.

you can check your engine temp, it gets too hot, check your relief spring.

if it fails it shouldnt contribute to spun bearings

[2Mitsus]

Originally Posted by mikes2nd

agreed, i have been reading forever about people shimming the relief spring...

and here since i never looked it up, thought it was for the whole oil system.

its not, that spring is for the oil cooler.

you can check your engine temp, it gets too hot, check your relief spring.

if it fails it shouldnt contribute to spun bearings

Maybe I dont understand your post correctly...
The oil cooler bypass valve and oil pump relief spring are 2 seperate things.
The oil pump relief spring (what is commonly shimmed) is what is going to limit your max oil pressure (at least that's what I believe it does).
The oil cooler bypass valve is what blocks off/permits oil from passing through your oil cooler.

What I'm saying is that if that oil cooler bypass valve is stuck closed (or only partially open), then your oil will not be cooled as well as it could, possibly leading to lower oil pressure when the oil heats up.

[drone007]

anybody running a real oil pressure gauge? it should be easy to see if your pressure changes when the valve opens, shouldn't it?

[2Mitsus]

I'm running a GReddy gauge.
An oil temp gauge would be ideal, but I don't have one.

I disassembled the stock valve, rendering it useless, so all oil is always going through the cooler (couldn't find the proper size plug, either m23x1.5 or m22x1.5), while I wait for my new valve to arrive.

Haven't driven it yet, maybe will tonight. I'll report back with results.

[Multiades]

I did actually disassemble one of these valves a while back. IIRC it was just a spring-and-plunger arrangement. I was planning on examining the assembly in detail but I think it was either lost or thrown out a while ago.

If I can scrounge up another one I'll check it out.

While I think this is a *possible* contributor to failures, I don't think it is a likely one. The mechanism seemed pretty simple and fool-proof (if anything more foolproof than a coolant thermostat -- fewer parts). The best/only way to check its operation would be to install an oil temperature gauge and check it vs. the specified thermostat temp in the service manual (not sure about the exact spec).

Checking up on the oil cooler and oil temperature is probably a good idea on an engine that is generating SO MUCH HEAT -- the expected thermal side-effect of producing 500-600hp for some owners.

-Chris