Low Oil Pressure Light at idle 1997 M3/4/5

[Tehvic]

Hey guys,

So I finally bought one of my long standing dream cars... an unmolested 1997 M3/4/5 in Estoril with about 113k on the clock. PO drove it short distances for the last 15 years. He has done extensive work to try and get this solved, including bottom end re-builds, oil pump, etc etc... but to no avail. I've done a ton of searching online and found a couple of leads but I figured I'd bring my super specific question on here...

The car idles at about 500 RPM, and on hot days, at temperature, and only at idle, the low oil pressure light flickers. On really hot days, it'll stay solid but only until I raise the RPM to over 650. It never comes on at operational speed. Now in the manual itself, BMW talks about that this is normal. I've owned two other M3's (1995 and 1996) and never saw this. The only lead the PO found was the oil squirters that are mounted mid engine... which I feel like would be a strange and random occurrence as ALL mechanics I've talked to have never even heard of this issue. (while it makes sense), I'd hate to do a full rebuild just to find out I was wrong.

I've noticed that if the nose of the car is pointing up, that it comes on less and sometimes not at all. If the outside temp is cool, it doesn't do it. There's no bogging in the motor, no backfiring, nothing.

He has been running 10w60 in the motor. I vaguely remember someone talking about having to slightly overfill the oil. Is that something you guys are doing? The last M3 I owned was almost 10 years ago and I'm feeling like this may be a aging issue?

Any help would be greatly appreciated.

[XnWarden]

The idle sounds a little low. Hook up an obd scanner and see what the idle rpms actually are. Sounds like possibly a faulty oil pressure switch

[Eric93se]

You should be running something like 5w-40 for colorodo. Your idle should be more like 650rpm.

Find out if he checked the oil pickup tube for cracks.

- - - Updated - - -

You can also try replacing the oil pressure switch if it hasn't been done.

[Nate047]

Hey man, I have the same problem. There's a pretty good thread about it right here:

https://www.bimmerforums.com/forum/s...e-at-Idle-Info

[Tehvic]

Thanks for the reply guys... I'm an idiot and ended up double posting this in the thread that Nate mentioned... I appreciate your advice!

[NeilM]

I haven't been able to find a BMW spec for idle speed, but anecdotally 500 rpm seems low. Idle speed is not adjustable as such, since it's controlled by the ECU via the idle control valve. Some aftermarket engine tunes will bump the idle a bit. The ICV is located under the intake manifold, and is certainly known to malfunction, or to leak vacuum at its rubber gasket mounting. A small vacuum leak anywhere else in the intake tract (also common) may also affect idle.

10W-60 is an unusually heavy weight oil to use in this engine, and wasn't even readily available when the car was current. AFAIK BMW started using it with the E46 M3's S54, which had rod bearing issues in the early versions. Oils commonly used for the S50/52 are 15W-50 for track/high ambient and 0W-40 or 5W-40 otherwise. I wonder whether the PO's use of 10W-60 was an attempt to address oil pressure issues?

It's definitely worth checking for the dreaded cracked oil pump pickup tube, but man, it's a royal pain to do.

Without an actual oil pressure gauge it's not really possible to draw conclusions about the state of an engine's lubrication system. You can buy shop oil pressure test sets for smallish money (Harbor Freight, etc.), or fit aftermarket dashboard gauges at rather higher cost.

Neil

[jayjaya29]

Run a full quart over full. I betcha the pickup tube is cracked.

[Tehvic]

Thanks guys! I'm running 7 quarts now. Feels pretty full as I'm above the second hash mark...