help! losing oil pressure

[kgls]

I have a 1992 Chrysler Daytona 3.0L MMC
i have recently striped down the engine replaced all the seals and gaskets. after i put the engine back together i lose my oil pressure after it warms up. i was told that it was probably the main bearings so i replaced the mains and connenting rod bearings. and i still have the same issue. I'm thinking at this point it could be the oil pump. i was also told the relief valve could be getting stuck open. it does not seem to be catching to be stuck open. i also found a form that says to put a washer under the releaf valve spring. does anyone have any suggest on what is the issue and how to fix this?
thank you

 

[expat]

What actual pressure readings are you getting?

It is normal for oil pressure to drop as the engine warms. but without actual psi figures, it's impossible to say if you have a real problem.

 

[Eddie]

How are you checking the oil pressure? Good gage?

 

[kgls]

Tested it with to differnt gauges. when it starts up 80 psi i think that got to be close to normal the longer it runs the lower it gets at idle less then 9 psi it even will drop below what the gauge can read, about 0 and the engine idles ruff rev it up it will back up and when it reaches idle again its up but still below 9 psi. i am using am aftermarket pressure gauge, when its fixed i will hook the factory gauge back up.

 

[kgls]

The factory gauge is what let me know about the problem giving me warning light with a chime. so Im pretty sure there is an issue, i know the pressure drop when the engine warms up. but i also know that there is a point that it gets too low. and when the cars warning light comes on i think thats a good indication that something is wrong, so to be sure i hooked up a mechanical gauge to be sure it wasn't the gauge.

I really dont get it. when the engine gets as warm as it will get, and the cooling fan has come on and off 3 times the pressure still drops to where the gauge barely reads it.

 

[dave2009]

I had the same sort of problem with a crate engine one time. It ended up being the cam bearings. If you are getting verifiable oil pressure when first the starting engine and it continues to drop, the oil is bypassing somewhere internally. I would not typically assume the oil pump but it is possible. There are only a few places the oil could be bypassing: main/rod/cam bearings or the oil pump.

 

[kgls]

thanks Dave,
Im hoping its not the cam bearings when i striped it apart i intended to replace the cam bearings i was told be the head rebuilder that cam bearing are part of the head and could not be replaced. if i recall right i did call around to see if i could get bearings, and couldn't. what sucks is that the oil pump is part of the front of the engine around the drive shaft. it +$200 for a new one. however i see rockauto.com has a rebuild kit...
I look at the manual on that engine it does say that that engine should have 6 psi at idle i did put washer behind the pressure relief spring to get it to 9 psi... i guess i will have to test it to see if it holds at around 9 or if it drops to 0 psi again. it's the dropping to 0 that bothers me, if the car reads it low. but the pressure is 6psi or above. i can live with that. but dont want it to drop to 0 and leave me stranded somewhere if i can avoid it.
My goal is to get it to last till swap out that engine. and put a 318 in its place.

 

[expat]

I'm surprised that the washer behind the relief spring made a difference.
The relief spring relives MAXIMUM pressure, it does not produce pressure.

 

[CATERHAM]

Originally Posted By: expat
I'm surprised that the washer behind the relief spring made a difference.
The relief spring relives MAXIMUM pressure, it does not produce pressure.

Exactly.

At what rpm does the engine idle at?
What exact oil are you running?
At what rpm does the engine reach it's maximum hot OP, what is it and how does that compare to the factory spec'?

 

[expat]

I now wonder if the relief valve is seating properly?
Perhaps some crud on the seat?

 

[dave2009]

Nothing produces pressure. Pressure is defined as: "the resistance to flow." Therefore if you have low volume of oil from the pump or a major internal leak you will have very low oil pressure.

 

[expat]

Originally Posted By: dave2009
Nothing produces pressure. Pressure is defined as: "the resistance to flow." Therefore if you have low volume of oil from the pump or a major internal leak you will have very low oil pressure.


However, if adding a washer to the relief valve improves that 'Low' oil pressure.
(Remember, this is a valve that should normally remain closed unless pressure exceeds the designed maximum)
Then I would assume that the valve was not functioning properly in the first place.

 

[tinmanSC]

Do you know what the oil pressure was before you worked on the engine? This oil pressure would be completely normal for the Toyota 2JZ 3.0L engines I own. Lowering at rough idle is normal, it's not the oil pumps fault. Rough/staggered idle would cause low oil pressure, not the other way around, so the pressure when the engine is not running properly is a symptom, not a originating cause(unless an oil-actuated variable valve setup is used, i guess?. Did you have a manufacturers guide when you rebuild this engine? Does it indicate what the standard oil pressure should be at idle and, say, at 3000 RPM?

Edit: Sorry, i just read your other post indicating 9 psi would be in the normal range. Sounds to me like you have an issue with rough idle, not oil pressure.

 

[demarpaint]

A long shot here but worth a try since you won't have to open the engine to find out. Is the base idle set properly? As mentioned ^^^^ too low an idle speed can also have an effect on oil pressure too.

 

[mechtech2]

Shimming the relief valve spring will have no effect when warmed up.
It is losing pressure for other reasons.
All that is left is the pump being weak/loose, or maybe passages that are partially plugged.

This assumes the bearings were properly sized to the crank! Worn journals may still be too loose with new bearings!