M42 Oil Pressure light

[CFeld]

So it's coming to winter and I just rebuilt the m42 I am running (all new gaskets and bearings). I am running 10w-40 as of right now, and I plan on doing the first oil change this weekend. The oil light comes on when the car is at operating temperature and below 1k rpm. It also comes on sometimes when I start it. Also it make an aweful racket sometimes just after I start it (like the tappets have no oil) for anywhere from 10 seconds to a couple minutes. The oil rotor looked fine to me as well as the pressure relief valve.
Should I start by filling oil through the filter housing? Does that make a difference? I live in chicago so it's about to get cold, I was wondering what weight I would use because maybe I am not using the right weight and thats why the light is coming on.

[CFeld]

bump

[downforce22]

You should probably start by making sure you have enough oil by checking the dipstick. If it below the low line, you fill it by opening the cap on the valve cover

[TobyB]

I think an oil pressure gauge would be a good start- see if it's really low.

If it is, I'd suspect a gross leak internally somewhere
(filter housing, upper oil pan)
or something messed up with the drainback valves, maybe.

t

[CFeld]

The oil is up to the higher line. I have a light right after a start and it quickly goes away (10sec-20). It only turns back on at idle after the car is warm. All the gaskets are new and at least externally there are no leaks anywhere. And by drainback valve do you mean the pressure relief valve? I think from doing some research I am going to try and use slightly higher weight, non-synthetic oil and a different oil filter (since the one I put it, though new, was sitting around for 10 years. It also still rattles after almost all start ups, meaning the tappets are drained, is this because the oil isn't a thick enough weight to stick? Thanks

[TobyB]

The M42 has at least one, if not 2 depending on age, valves that hold oil up in
the head. There's one in the filter housing. Anti- drainback, I seem to remember them being called.

But my internet guess, having had cars with galley leaks, is that you have a leak somewhere internal.
The light comes on at like 8 psi, and you should have a lot more than that with fresh bearings...

t

[ccsdo5]

I would put an oil pressure gauge on the back of the cylinder head. That's where I put mine, figuring it is like the highest point of the engine. My sensor was all sorts of messed up for a while so it scared me thinking I had no pressure but turns out sensor was just bad in the filter housing.

[CFeld]

Unlikely the sensor is wrong due to repetitive issues. Every time I start the car up the oil light is on for 10ish seconds. I just checked on real oem and there is no part listed in the housing of course. I think I found a link to it on ecs tunings website. Is there a way to clean it or should it be replaced?

[CFeld]

Just checked a spare oil filter housing I have laying around, there are 2 drainback valves, so you were right. It may not be working correctly if I am using to loose of an oil weight, I'll check tomorrow when I do the filter.

[CFeld]

No dice on the idle issue. The oil light now doesnt go on at start tho and coolant temp is ok.

[TobyB]

Every time I start the car up the oil light is on for 10ish seconds.

This is what makes me think you're losing oil in the galleys when it sits, and that
the low pressure at idle's really a leak somewhere inside the engine.

On mine, the oil light comes on when I turn the switch to 'on', and as soon as the
engine catches, the oil light goes off.

On the 2002's I've had that popped o- rings in the bypass valve passages, they all behaved
as your engine is doing- a long time for initial oil pressure to build, then a lower-than-it-should-be
idle oil pressure.

That's what I'm basing my internet guess on.

You could test my internet guess by switching off, and then immediately restarting. If it goes out immediately,
then wait longer and longer intervals before the restart. If it takes longer for the light to go out
as your 'wait' time increases, that really points towards a leak somewhere.

hth
t

[bmwman91]

Did you replace the oil pressure bypass parts (the plunger & spring in the timing case)? If those bits were missing or jammed open, you would not get much oil pressure. The relief valve design was updated due to the original metal one jamming, so the correct part to have in there is a plastic one.

[CFeld]

Did you replace the oil pressure bypass parts (the plunger & spring in the timing case)? If those bits were missing or jammed open, you would not get much oil pressure. The relief valve design was updated due to the original metal one jamming, so the correct part to have in there is a plastic one.

I put back in the original metal one so that may be the issue. Should I buy new upper and lower oil pan gaskets as well when I replace it with the updated one? Should I buy a new spring for it as well? Also I am still having the oil light turn on for cold starts. Is that related? I got 8 psi at idle from the filter housing, so just low enough to trigger and 60psi at near redline warm. Thanks and I really appreciate the website you have for your car, I've used it a bunch.

[CFeld]

This is what makes me think you're losing oil in the galleys when it sits, and that
the low pressure at idle's really a leak somewhere inside the engine.

On mine, the oil light comes on when I turn the switch to 'on', and as soon as the
engine catches, the oil light goes off.

On the 2002's I've had that popped o- rings in the bypass valve passages, they all behaved
as your engine is doing- a long time for initial oil pressure to build, then a lower-than-it-should-be
idle oil pressure.

That's what I'm basing my internet guess on.

You could test my internet guess by switching off, and then immediately restarting. If it goes out immediately,
then wait longer and longer intervals before the restart. If it takes longer for the light to go out
as your 'wait' time increases, that really points towards a leak somewhere.

hth
t

All the gaskets were replaced and sealed properly, so I don't think that would be it. I think it's more likely for the pump to be worn. I put and oil pressure tester on the filter housing hole yesterday and I got about 8psi of pressure at warm idle and 60psi at near redline using 20w-50. There a chance I have a leak but I have no idea where it could be. It's not burning any oil so the only place I think it could be leaking through is the drain back valve (which seemed ok) or the pressure relief valve.