Low oil pressure when warm
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Senior User
Joined: Apr 2006
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From: Waco, Tx
Low oil pressure when warm
Hey guys, after swapping the heads out and putting a new ignition/dizzy on my 390, my oil pressure starts to drop after running for about 15min. It's within the normal limit but is still sittin on down there. When first reassembled it didnt do this but now it seems to be getting worse. If I'm at highway speed then it is alright at best and then coming off the freeway and at low speed after that it drops....dont have new guages just the factory so dont have any numbers... it usually runs between the M and A of NORMAL now it drops to the N/O area haha any help would be greatly appreciated.
Logistics Pro
Joined: Oct 2005
Posts: 3,785
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From: Mddl A MexCans
I'd put after market gauges on it. Mine reads about 25 on the stocker and the SunPro is about 48-52 at idle and drops to about 42 when warm. The stocker is then in the high teens area so 
wouldn't count on the stock stuff for much IMO. If you dont hear/see signs of low oil(clatter/temps) it probably isn't an issue
wouldn't count on the stock stuff for much IMO. If you dont hear/see signs of low oil(clatter/temps) it probably isn't an issue
Lead Driver
Joined: Jan 2003
Posts: 9,893
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From: Ohio
Stock gauges are good for telling you it HAS oil pressure, but that's it. If the sender is a bit off, plus gauge voltage is off, then you'll have low readings. Get yourself a nice cheap mechanical gauge and see where you're at.
My 150K mile stocker idles at 15 hot, runs down the road at 45 psi.
The rear main seal has nothing to do with oil pressure. The seal only helps keep the oil from the rear main cap from leaking out the back. With an old rope seal, it's only a matter of time before it leaks. It really gets bad if you don't run the truck much as the old rope dries out and then starts leaking.
My 150K mile stocker idles at 15 hot, runs down the road at 45 psi.
The rear main seal has nothing to do with oil pressure. The seal only helps keep the oil from the rear main cap from leaking out the back. With an old rope seal, it's only a matter of time before it leaks. It really gets bad if you don't run the truck much as the old rope dries out and then starts leaking.
Lead Driver
Joined: Jan 2003
Posts: 9,893
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From: Ohio
The restrictor is basically to keep the oil down at the mains/rods, but it will not actually increase the oil pressure(by much of any). Unless your rockers area severely worn and leaking oil past to the extreme that it does make a difference.
BTW, the restrictor is NOT a factory part. It is only put in by us to keep oil down south.
BTW, the restrictor is NOT a factory part. It is only put in by us to keep oil down south.
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Senior User
Joined: Apr 2006
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From: Waco, Tx
to clarify a little.... after the pressure drops it doesnt come back up, once it's low..it's stays low
and now i seem to be having a new problem, it keeps wanting to die at idle..sometimes it won't and sometimes it will, it starts coughing/sputtering and wants to die, very annoying at lights on hills! overall it seems to be losing a little power not much but noticeable. problem with fuel delivery?
and now i seem to be having a new problem, it keeps wanting to die at idle..sometimes it won't and sometimes it will, it starts coughing/sputtering and wants to die, very annoying at lights on hills! overall it seems to be losing a little power not much but noticeable. problem with fuel delivery?
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Cargo Master
Joined: Apr 2004
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From: Golden, CO
Originally Posted by JesusRocks
Hey guys, after swapping the heads out and putting a new ignition/dizzy on my 390, my oil pressure starts to drop after running for about 15min...
it keeps wanting to die at idle...
it starts coughing/sputtering and wants to die...
overall it seems to be losing a little power
it keeps wanting to die at idle...
it starts coughing/sputtering and wants to die...
overall it seems to be losing a little power
Re-torque the heads and intake?
Any cross-contamination between oil and coolant?
Do a compression test?
There are a couple ways to find an intake leak under the manifold:
1)Find a shop that has a smoke tester, those are pretty slick.
2)Take the truck out where you can wind it out in 2nd gear and take your foot off the gas. If there is an intake leak under the manifold, the high vacuum will suck oil into the cylinder, and out the tailpipe.
Good luck!
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