M50 running, oil light on, why?

Post Sun May 22, 2011 6:55 pm

Had my M50B25 vanos running again today, seems to be going good but the vanos unit seems to be making a bit of noise. Time to check that later.

In the meantime I was wondering if I should worry about the dash oil light staying on? What does this actually mean, oil pressure or could it be any fault?

Only unconnected sensors are tank breather valve and lambda.

Post Sun May 22, 2011 7:49 pm

If the vanos is making a load of noise it genuinely could be because you have naff all oil pressure, so be careful.

Check you have the brown temp sensor and oil pressure plugs the right way around as the plugs are the same

Post Sun May 22, 2011 8:48 pm

Hmmmmm, funny that I'm pretty sure it was not on before.

Of course the front is jacked right up at the moment but no more then would happen on a steep hill.
Is there any way to check oil pressure? If it is naff what are the possible causes, pump?
I know about the pump sprocket nut and I threadlocked it.

EDIT: Thanks E30Lad, I'm pretty sure the sensors are right as I checked all the cable colours against the wiring diag. I will check though.

Post Tue May 31, 2011 9:26 am

Update on this.

With the front lowered the oil light does go out after 10-20 seconds (at idle), but something is obviously not right. I replaced the oil filter, which was a bit odd 'cos the one that came out was a metal cartridge and the Bosch replacement was paper. Didn't make a nioticable difference.

Anyway, I've bought a mechanical pressure tester from the bay and will report back on findings.

At this time I'm thinking that pressure starts low and stays low would mean oil pump, pressure starts low but then becomes normal could mean pump control valve. I'm 99% that the gasket was good before I closed it all up so that shouldn't be the problem. I could get lucky and have a faulty sensor but my money is on the valve.

In any case it's likely I'll have to pull the engine out again, which is going to upset the missus who wants to know when I'm gonna finish the damned thing already!

Post Tue May 31, 2011 12:56 pm

I had the oil pressure switch go on my M50 shortly after getting it on the road. Worth trying another for the time it takes... M20 ones fit.

Post Tue May 31, 2011 1:07 pm

Was your oil level correct? With the pickup at the front the oil will run to the back when the car is lifted at the front (or going uphill/accelerating hard) I always overfill an E34 sump by about 1/4 of an inch on the dipstick for this very reason

Post Tue May 31, 2011 3:32 pm

The problem does seem worse when the front is lifted, but a cold start even with the car level leaves the light on for 30 seconds. subsequent starts (within a few seconds) the light goes out immediately. That's why I reckon control valve.

Still. good tip on the oil level, It's about on the max line right now I'll maybe give it another pint or 2 (lucky lady).

Should my filter be paper?

Post Fri Jun 10, 2011 11:54 am

Another update.
Got my mechanical oil pressure gauge plumbed in and tried last night.

Results are that the pressure is approx 7psi at idle which is normal, but does seem to take a while to get there. It settles at about 20psi at 1500rpm and at about 35psi at 2500rpm. Seems a little on the low sie at high revs to me.

Some wierdness though:
It takes a while to reach any kind of pressure and it's clear that the oil always drains out of the filter housing with the engine off. Is this normal? I thought that's what the control valve was for.
Also, the oil pressure occasionally (even at idle) climbs much higher and then falls back again, what's the cause of that and is it normal?

Post Fri Jun 10, 2011 9:18 pm

There is a valve in the oil filter housing that stops the oil draining out, do you have a good O ring on the long bolt? This lets the oil drain out for you to do an oil change, you need to get the bolt out quick and lid off to see if there is any oil still in there.

I have some audi gauges in my track car M52 engine and the pressure is 1 - 2 bar at idle, goes up to around 4 bar at high revs IIRC

Post Mon Aug 15, 2011 1:05 pm

So I finally got around to taking the engine out to inspect the oil pump. This conversion is taking forever!

The news is that I found a couple of problems which explain the low oil pressure.

I took the oil pump apart and it all looks good, was at a loss to understand the issue. But I noticed that the mesh inside the oil pickup tube was partially blocked up with crumbs of metal and plastic. Now I'm 99% sure this didn't come from my engine, but of course the tube would have come out of a different car so I assume the guy who put it together (bought installed in the engine) was just a bit stupid. So I decided to take the pickup tube off and clean it out properly.

That's when I noticed the REAL issue. The guy bolted on the pickup tube with the gasket upside down. So part of the gasket obscures the oil inlet to the pump, but probably more importantly the flange is not sealed all the way around, so it would have been like sucking on a straw with a hole in it. What a dick!

Anyway, I've carefully cleaned out the mesh and am buying a new gasket. The bottom end looks V Good with no swarf or debris in the sump or drained oil, so I'm pretty sure the pickup tube came from an exploded E34. Don't really want to start opening up bearing caps etc...

I'm also probably going to buy new pump rotor inner and outer while I'm at it. The pump runs mostly smoothly and is tight, bear in mind it's dry, but it does occasionaly 'catch' a tiny bit and clicks a little as it turns when dry. This may be perfectly normal, opinions would be welcome.

BTW, anyone know if the outer rotor has a right and wrong way round? It has a little square dimple on one of the teeth on one side?

Post Mon Aug 15, 2011 1:34 pm

Well worth buying new innards for the pump, its only about £30 for what you need. Also fit a new pressure relief valve spring while your at it.

Post Mon Aug 15, 2011 1:43 pm

Thanks Dan.
Which way round does the outer rotor go?

Also, you previously mentioned a valve in the filter housing that prevents the oil draining, I can't find this on any diagram or at realoem. Any hints?

Post Mon Aug 15, 2011 10:35 pm

I cant remember about the pump without looking at one, I mentioned above about the drain on the M50 alloy top filter housing, the long bolt has an O ring on the end, this seals the drain tube that lets the oil drain back to the sump when you do an oil change. I cant remember how the actual valve works on an M50, but ive found several fcked M52 and M54 valves lately - http://www.e30zone.net/modules.php?name ... c&t=201086