low oil pressure

[mclovn82]

so i rebuilt my engine and im kinda scared to run it cause everytime i start it up the oil pressure sits at about 40 and just disappears as it warms up and when it idles it has no oil pressure but when i give it gas the oil pressure picks up i thought this would of stopped when i rebuilt it but it stayed the same i even went and got a mechanical guage to double check i can pull the hose off the guage and its barely pumping but its pumping and im running a 40 weight oil is it my bearing my oil pump or do i need a thicker oil and im in texas and its really warming up here

 

[Mil1ion]

How soon after you start it does the pressure drop ?

Have you checked the psi at idle speed ?

Is the orifice in the S/U slightly plugged

 

[mclovn82]

dude i just gotta say your freaking awesome at answering my questions and the pressure drops off as the engine warms up and ive only let it idle but right now it idles at like 1500 and wont get any lower im searching for a vaccum leak right now as for the sending unit is that the piece on the block behind the intake manifold if so i removed that for the tubing for the mechanical guage

 

[LEB Ben]

How low and how far does it drop off and how long does it take to drop off? These things can run on 5-7 psi, but being a fresh rebuild, it shouldn't. Your start up psi isn't bad, but sounds a little a low. Idle psi should be around 25psi and rule of thumb is 10psi for every 1000rpm increased. I think exact numbers and exact times of when you're having problems would help diagnose the problem. However, at this time, I'd either guess bearing clearance or oil pump. But my gut says since this was happening before the build, it's a different issue all together.

 

[cumminsnorth]

Is it possible that you left a oil gallery plug out somewhere inside the engine? I just rebuilt mine and cold at idle i'm running 75psi cold and 38psi warm at idle with a standard volume oil pump. Did you check your bearing clearances when it was rebuilt?

 

[73F100Shortbed]

My engine with a few thousand miles on it has 50psi at start up and warm at idle with 650rpms is anywhere from 28-30 psi. You shouldn't have to use thicker oil on a rebuilt engine to get oil pressure higher. Only if it is worn out. What engine do you have? On my 302 the oil sending unit is on the left side of engine near the oil filter not behind intake.

 

[Mil1ion]

What engine is this?

351M/400 ?

IF SO DID YOU NOT do the oiling system fix when you rebuilt it ?

 

[Mil1ion]

idle too high ...check your timing value

 

[LEB Ben]

IF SO DID YOU NOT do the oiling system fix when you rebuilt it ?

There's an oiling system fix? Care to share?

idle too high ...check your timing value

I noticed that too, but didn't think that would affect oiling. To the OP, timing should be somewhere between 10-14* depending on trans on a relatively stock engine.

 

[Mil1ion]

http://351cleveland.wetpaint.com/page/Oiling+tech

You just have to install an oil restrictor kit to raise the pressure.

http://www.pricemotorsport.com/Oil_Restrictor_Kits/oil_restrictor_kits.html

 

[LEB Ben]

http://351cleveland.wetpaint.com/page/Oiling+tech

You just have to install an oil restrictor kit to raise the pressure.

Sweet...thanks for the link...a good read.

 

[gsxr1238]

I go along with these guys.Excessive bearing clearance,excessive lifter bore wear,internal leak or casting flaw.Is the oil pump new?Could it be it is worn beyond limit for the gear lash?Could be a stuck bypass(open)in the pump.What shape is the pickup tube and screen in?What do the oil pump driveshaft and distributor drive socket look like?Seems like a previous problem is still lurking in there.Let us know what you discover.

 

[Mil1ion]

He states he rebuilt the engine si suspect he also did all the bearings hopefully with bearing tape

 

[mclovn82]

i rebuilt the top end the engine is a 460 the only bearings i had the guy look at were the cam bearings and it holds oil pressure till the temp gets to about 190 then its at zero now if i idle it up some the pressure comes back depending on the rpm

 

[gsxr1238]

Has the oil pressure been low in this engine all along,or is it a recent development?My service manuals state that a 460 should carry 50-65 psi@rated speed.Rated speed is usually in the 2000 RPM area or approx. 60 MPH.I would look at the rod & main bearings for wear/damage.Oil pressure will usually drop as the engine reaches operating temperature.This is due to the oil clearances increasing as temperatures rise.Check the oil clearances.The rods and mains are .001/.003,as are the cam bearing clearances.Inspect the oil pump,drive,pickup tube,and screen.

 

[Mil1ion]

See .. what more information does?

That is normal pressure change as the con-rod bearings are subject to more wear and as they heat up.

Note to engine rebuilders.. when you build the top or the bottom ONLY, expect the one you didn't do to require it soon.

IMO, you must

 

[73F100Shortbed]

I assumed when you said you rebuilt the engine that you rebuilt the whole thing. Might as well do the bottom now. I'll go more toward bearing issues in the bottom now.

 

[chuck101st]

Usually when oil pressure drops off after an engine is warmed it is due to cam bearrings being worn...

 

[78freewheeler]

well IF i read that link correctly then unless your turnin that bad boy above 6200 your fine. unless i read it wrong.

 

[mclovn82]

yeah im going back into the motor now i just really didnt wanna tear the whole engine apart im ready to driver the thing already