Anyone ever seen an oil cooler tstat stick open?

[strad]

Just wondering what the possibility might be before I go and dig into it. Can anyone think of a way to check it without taking it apart?

Symptom is that oil pressure suddenly started taking slightly longer to turn the light off at startup. The oil pump is not the culprit. Key words are suddenly and slight.

[jlevie]

Could be a bad pressure switch, or it could be a problem in the engine. Best to have a gauge temporarily connected to see what the oil pressure is actually doing.

[strad]

Update: the gauge says the motor is making 50+psi at idle. Which is good, but outside of what the Bentley manual suggests for idle pressure. Elevated engine speed sends the value up to 70+ psi. these are engine cold numbers.

So is Bentley wrong? What have other people seen for idle pressures in a healthy M20? And, I still might have the issue that titled the thread.

I notice that if the nose of the car is pointed downhill it takes longer to turn the oil light off than if the nose of the car is pointed uphill, when the light goes off immediately. This leads me to wonder if the oil cooler loop is somehow involved. Help me out here guys.

[matt]

Hot idle should be 7-10psi. Should gain 10psi or so per 1k RPM.

[strad]

Hot idle is 24 psi if my brand-new gauge is to be believed.

I'm starting to wonder if anyone here even knows what the effect on startup oil pressure would be if the oil cooler thermostat were stuck open.

The sender is a brand new one, and behaves exactly like two others (the old one and the one I borrowed from my 318i, which uses the same part number).

[matt]

Hot idle is 24 psi if my brand-new gauge is to be believed.

I'm starting to wonder if anyone here even knows what the effect on startup oil pressure would be if the oil cooler thermostat were stuck open.

The sender is a brand new one, and behaves exactly like two others (the old one and the one I borrowed from my 318i, which uses the same part number).

I don't think there would be any effect.

[jlevie]

What oil is in the engine?

[strad]

I think 10W40. Either that or 20W50. It's Castrol GTX. I've switched back and forth and forgotten what I put in there in trying to alleviate this problem. Ambient temps are 50+ F

[nando]

I'm getting 7-10psi at hot idle here. but it takes forever for my oil to warm up!

[strad]

Believe it or not, this problem was caused by the Mann filter I was using. I switched to a Bosch filter and the problem went away.

I do not know why the Mann filter caused this issue. I suspect it's a manufacturing defect rather than a design one, since I have used filters manufactured by them in an earlier lot and they were fine.

[euroshark]

Wow, that's odd... I always use Bosch or Purolator filters and have never had problems, but I have the canister filters (silly M30s ). Idle in my Alfa Milano 2.5 was 30psi and 50psi at 3000rpm... It was nice having a car that came stock with an oil pressure gauge... Even though none of the other gauges ever worked properly.

[mops]

the exact oil press figure will depend on:
1. type of oil used
2. how warm the oil is.

healthy m20, cold idle = 60 psi (without reeving the engine)
ideally warm idle oil press should not fall below 15 psi.
general rule (all engines) is 10 psi per 1000rpm, is there's any less then there might be a problem.