IT-Guy

I recently rebuilt my LT1 and have no oil pressure at hot idle. Someone please give me some advice.

I have searched the posts on this subject and talked with several engine builders and also Melling. They all suggested it was a bad pump. I replaced the pump last night and it did not correct my oil pressure problems.

Some background on the issue:

The engine was just rebuilt. All bearings were replaced and clearances were all within spec. At cold startup I have about 30psi of pressure and good pressure throughout the RPM range (60+psi at high RPM with no drop off). Once the engine is hot I have zero psi at idle (I have verified this with a mechanical gauge). I have about 10~15 psi at 1200 RPM (hot) and will steadily climb with RPM as would be normal.

Does anyone have any ideas? Is there anything in the oil passages that would cause this behavior? The engine runs great and makes no unusual noises even at hot idle. Can these symptoms point to anything besides the oil pump? Someone please help!

Fastbird93

This may seem dumb, but could it possibly be the oil pressure sending unit going bad as it heats up, or a wire resting against a hot part maybe???

GreenDemon

Are you using a stock oil pump?
Have you checked the pickup & screen for blockage or movement?
What brand & weight oil are you using?

IT-Guy

I am using the stock replacment Melling M-55a pump (both of them were this model). The pickup was welded on the first pump and there was no debris in in the screen and was 3/8" above the base of the pan. The one I put in last night was pressed in.

One the first pump I stared out running 10W-40, then 20W-50 (same results). I am currently using 10W-50.

LT4orbust

what is called for at idle hot? i thought that was about right, or at least within limits, i may be thinking of a different make specs but i know for sure some are even lower and still within limits

GreenDemon

Not within specs. Although the 1200 rpm one might be but just barely, I think the book specifies 6 psi at idle. Although most people see 20 psi at idle. Your other reading seem average, though.

Maybe someone will chime in with an idea. I'm out of ideas if you say everything was put together correctly. The oil is certainly heavy enough...

apick42

Is your oil pressure steady at above idle if not the sending unit is bad or the wire is loose. But if a mechanical gage reads zero than even though you have a new pump something is wrong with it buy the way do the lifters tap at idle this would mean no oil i had the same problem a long time a go had
pressure at around 1k and above but at idle was at zero but there was no tapping from the lifters and than one day they started to tap i pullled the valve covers and sure enough no oil was on top put it was pumping enough to lube the bottom i guess i was lucky , replace the pump and every thing was fine oh and this was on a fresh rebuilt engine so check out the pump again.