can't make sense of this, please help

Sat Dec 12, 2009 4:56 pm

I have a M20 2.5 and the problem started with oil pressure light coming on at idle when hot. Okay when cold.
I checked the wiring and replaced the sensor with no change.
Now I've replaced the oil pump with a complete new unit using the existing drive shaft, put it all back together and now the light is on all the time. I gave it a few seconds then switched it off, a bit gutted. So now I have no oil pressure and cannot think what the problem is. Any help appreciated.

Sat Dec 12, 2009 5:32 pm

The symptoms suggest worn shell bearings I'm afraid

Sat Dec 12, 2009 5:54 pm

e301988325i wrote:The symptoms suggest worn shell bearings I'm afraid

That thought was on my mind and could be the problem I guess. I was thinking if I changed the pump and it was the same then engine wear would be the cause, however the new pump doesn't seem to be doing anything.

Sat Dec 12, 2009 5:59 pm

If you have the crank re-ground and fit new matching bearing shells along with new piston rings you will see a difference.
Oil pump will only pressurize when there is something to pressurize.....

Sat Dec 12, 2009 6:04 pm

http://www.realoem.com/bmw/showparts.do ... g=11&fg=10
part no 20, the pressure relief valve. After racking my brain, there was a stain on the inside of the sump under this valve? I always thought the relief valve was built into the pump.

Sat Dec 12, 2009 6:05 pm

daimlerman wrote:If you have the crank re-ground and fit new matching bearing shells along with new piston rings you will see a difference.
Oil pump will only pressurize when there is something to pressurize.....

Was hoping not to have to resort to that, who knows maybe an engine swap on the cards.

Sat Dec 12, 2009 7:06 pm

Could be the new pump isn't primed - which would be why the oil light is on all the time now.. However the root cause of the problem the first time could well be shagged shells.

You could get a few more miles from it by sticking some thicker oil in - it only lights up the light when the oil is warm and thin, thicker oil is better at cushioning knackered bearings. This would be a temporary measure however, as the problem is still there.

Sat Dec 12, 2009 7:17 pm

SkyRocketeer wrote:Could be the new pump isn't primed - which would be why the oil light is on all the time now.. However the root cause of the problem the first time could well be shagged shells.

that also crossed my mind as I didn't change the filter and wondered how it would get rid of the air locked in the pump discharge, how would I prime the pump?

Thing is the pump impellers look well worn on the old pump and the engine isn't complaining and still pulls like a train.

Sat Dec 12, 2009 7:27 pm

EVIR wrote: that also crossed my mind as I didn't change the filter and wondered how it would get rid of the air locked in the pump discharge, how would I prime the pump?

the pump needs something in it to create suction on the pickup, oil is ideal, though it kinda runs out as quick as you pour it in.. Packing the pump out with paraffin grease is a good compromise.

Sat Dec 12, 2009 7:35 pm

What If I take the filter off, would that allow the level outside and inside the pump to equalize I wonder. Maybe all is not lost. I think I'll take the plugs out and turn it by hand to see if I can get anything from it before giving up.

Sat Dec 12, 2009 7:48 pm

Nah, pretty much all the oil is in the sump, which is below the pump.

What you could do, which will be pretty messy but might work, is to pull the filter off, and try to pour some oil into the engine via the filter connection.

You'll have to choose carefully as there's an in and and out for the filter - one's the middle threaded section, and one is the chamber/jacket around it - I don't know which is which though (I could guess and suggest the centre section leads to the pump, but I could be wrong).

Do this whilst turning the engine over backwards by hand (plugs out) and you should see the oil sucked down the correct hole by the pump. In theory it'll blow the air inside it out down the oil pickup tube and eventually everything will be full of oil.

In practice you'll probably get oil everywhere and be none-the wiser that it actually worked

You'll also run the risk of overfilling the oil, so drain some out first..

Or simply drain all the oil, drop the sump and pack the pump with grease..

Sat Dec 12, 2009 7:54 pm

is backwards clockwise? thanks for the help.

Sat Dec 12, 2009 9:07 pm

willnz wrote:Have you checked that your electrical feed to the oil pressure light is not grounding itself somewhere? Run the motor and remove the wire from the sender and see if the light goes off.

If you were running bearings, you would hear it!

The pumps normally prime themselves, you can check if it is pumping by removing the filter, removing the green wire off the coil and giving it a short crank. (put a deflector in front of the oil filter mounting point into a catch tray so you dont get oil all over )

Well no nasty noises yet, going to pull the oil filter tomorrow and see if I can get the pump to lift.

Sat Dec 12, 2009 9:22 pm

My M20 gave no nasty noises and pulled well with the oil light on as well

Re-build with parts as described cured it,and it goes better as well.

Sat Dec 12, 2009 9:37 pm

Could be something as simple as the filter itself.
I had a 525e some time ago and after changing the filter one time it was doing what your 325 is doing. I had the pressure checked by gauge and all was well.

I then put on a genuine German BMW filter (as you can get Slovenian and other BMW filters) and the fault went away.

Sat Dec 12, 2009 9:58 pm

daimlerman wrote:My M20 gave no nasty noises and pulled well with the oil light on as well
Re-build with parts as described cured it,and it goes better as well.

The light was only on below about 900rpm, so fingers crossed it's not dead yet.

Sat Dec 12, 2009 10:00 pm

hennabm wrote:Could be something as simple as the filter itself.
I had a 525e some time ago and after changing the filter one time it was doing what your 325 is doing. I had the pressure checked by gauge and all was well.

I then put on a genuine German BMW filter (as you can get Slovenian and other BMW filters) and the fault went away.

That sounds weird, I got my filter from the oilman so I hope it's of a suitable standard.

Sun Dec 13, 2009 12:58 pm

just for completion in case anybody has the same issue, I removed the filter to allow the air out the system, upon doing this the pump flooded and oil light went out on the first crank.

not the best photo but you can see how the pump has destroyed itself, I found a lump of grit wedged in the suction filter.
Can't think how grit can get in there but there you go. Hopefully the filter will have caught the debris.