M42 Just Rebuilt: Oil Pressure question

[Gerta]

Oil recommendation?

[ForcedFirebird]

The sensor is grounded through the threaded housing. One single wire goes to it, but have a feeling it's no shorted if the light is going out.

Have a mechanic do a pressure test to validate the light.

[ForcedFirebird]

Lighter oil = LESS pressure at start-up.

[Gerta]

@ John - I have the tools for a pressure test. I agree which makes this a frustrating gremlin to chase.

Using the heavier oil, could it be causing a high reading which causes the light? The light does shut off when the car gets up to normal oil pressure (i.e. lessening of m42 lifter noise at start up).

I'll try it again today and maybe post a more accurate timeframe for the the light going out and engine noise.

[Gerta]

... and thanks Guys! I appreciate the feedback and assistance.

[ForcedFirebird]

Light will only come on for low pressure.

[Gerta]

Light will only come on for low pressure.

This is good to know. Thank you.

[bmwman91]

Did you accidentally swap the coolant temp plug and oil pressure plug? I did that once, scared the shit out of me. Oil light would be on and fade out as the engine warmed up.

Do you get a lot of lifter tick or timing chain rattle? If not then your oil pressure is probably fine.

[Gerta]

Bmwman, no I don't think I did. I have the usual lifter tick at start up with the M42, but it goes away very quickly and idles pretty quietly. The oil light is not on very long ... but the fact that it comes on at all for that <120 seconds or so at cold start up scares me. Warm start up, like after I drove it for 10 minutes stopped for 20 minutes and then restarted; it doesn't come on at all after ignition.

[bmwman91]

Yeah, I suppose that your coolant gauge would be totally buried in the red if you swapped plugs.

Weird behavior. Did you rebuild the oil bypass in the timing case? (the spring/cup thing held in by circlips) Maybe that is stuck open or the spring broke? There was an update to the cup part that not many E30 M42's ever got (switched from metal to plastic). I think that it was because the cup would seize in place or something.

Parts 5-8:

http://www.realoem.com/bmw/showparts.do?model=AF93&mospid=47305&btnr=11_0504&hg=11&fg=30

[Gerta]

Right. Coolant level never reaches mid point ... it is pegged a couple of ticks below half ... it runs and idles really well. I did rebuild the oil bypass with the updated part and new circlip to hold it in. I actually did that at the machine shop with the help of the machinist to because the circlip was a PIA.

[TobyB]

The oil filter housing has several backflow valves and holds quite a bit of oil-

when I did the timing chain and filter housing, I rolled the motor over to get pressure,
and it took FOREVER for it to fill and start pumping oil at pressure the first time.
I think I even had to pull a plug to get it to start pumping at all, letting air bleed out.

Now it's fine.

If you're running ok now, I wouldn't worry about it until it starts making more noise...

t

[Gerta]

Toby, it actually doesn't make any unnatural noises at all. Talking to a 50 year BMW mechanic, he thinks I should use a non-detergent 30w oil. It seems that there are a 101 recipes for breaking in an engine and none of them are the same.

[TobyB]

Yeah, true- but the cam grinders agree, you need a high ZDDP oil for a successful cam
break- in, and the ring guys agree you want a dinosaur oil for good ring seating...

I have used a standard 30wt with ZDDP additive, and I've used 'Break- in oil'
and both have worked.

hth

t

[AndrewBird]

You said you have a pressure tester, but never said if you tested it. Start here to make sure there is even a problem. If you have adequate pressure at start up, then the problem is electrical. If you don't have pressure, then there is something wrong with the engine.