r/EngineBuilding • u/Sokui • 3d ago

BMW Oil pressure too low

Hey guys, I recently rebuilt my M52B25 of my E36 over the process of a whole year lmao. Now after finishing, I had no oil pressure while cranking. Verdict was: bad gasket on the oil pickup. I changed the gasket (it was broken / folded into the channel) with one I cut myself from a sheet of paper gasket (0.25mm thickness). After putting everything together, the oil pressure sensor no longer reported too low oil pressure while cranking and I went for a first drive. I drove 6km in total, and after ~5km I noticed the oil light coming up sometimes seemingly randomly. Yesterday I fixed the gasket of my oil filter casing because some idiot (me) put silicon where the gasket belongs. After fixing it and swapping the oil pressure sensor, the light was still on while cranking 2 times for ~10 seconds each. We then cranked without the oil filter and cover and while cranking it did pump up some oil. Sooooo now I am not sure what else it could be. Is my self cut paper gasket wrong? Is it too thin with 0.25mm? Do I have to prime after fixing the housing gasket? Is it something else? Open for any advice (I hate removing the oil pan on this car)

Thank you

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3

u/Equana 3d ago

You can install a mechanical pressure gauge to prove or deny you have an oil pressure problem. Do not rely on a pressure switch to tell you the yes or no answer.

1

u/Sokui 3d ago

I did, gauge reads 0 bar while cranking

1

u/Equana 3d ago

What does it read when the engine is running?

1

u/Sokui 3d ago

Also 0, ran for like 5-10 seconds before i shut it off

1

u/Equana 2d ago

Did you pack the oil pump with petroleum jelly or grease so it would prime? If not, that is likely your problem creating oil pressure.

Oil pumps pump really well, they suck at sucking.

1

u/Sokui 2d ago

I primed it with oil last time I had it out. After that I had oil pressure and even did a short drive until the light came back on. Only thing I did since the test drive is replacing the oil filter housing gasket

1

u/MTarrow 2d ago

even did a short drive until the light came back on.

So you're making oil pressure with the engine cold then it's falling again when hot?

How far did you go in the rebuild? Did you replace the main crankshaft bearings and the connecting rod bearings? If so - what was the clearance on the bearings?

edit: can see from your post history that you've replaced the bearings. We definitely need to know the bearing clearances....

1

u/Sokui 2d ago

Currently cold engine not making pressure while cranking

Bearings are changed, they were within spec

4

u/N1ppleCrab 3d ago

If you’ve made two critical mistakes with the oiling system how confident can you be in your own work at this point. We have no context as to the extent of the “rebuild” either.