oil pressure issues?

[mad2smile]

i finally got my 390 running well. oil pressure was excellent at first, but after idling for about 15-20 minutes, my oil pressure dropped extremely low. the oil level is perfect, and when i had the engine apart, i scraped and vacuumed all oil passages as well as i could. i also installed a high-flow performance oil pump.

any ideas on what could be causing such an issue? could the pump be becoming un-primed? i have no clue whats going on. any help would be greatly appreciated.



***add*** all gaskets and seals were replaced on the engine, including the rear main seal. the only seals not replaced are the camshaft seal and valve stem seals. /add

[68swb]

how low is extermley low? did you replace the bearings? what oil weight are you using?

[mad2smile]

the bearings were not replaced. i know people lie, but the guy i bought the 390 from assured me it didnt use any oil. hopefully he was telling the truth.

low means bottomed out on the gauge.

um, oil... well, i found fully synthetic 15W50 Mobil1 on clearance for an excellent deal, so i used 3 quarts of that and and 3 quarts of conventional 5W20. so basically, im using partially synthetic 10W35.

im gonna try replacing the pressure sending unit. hopefully the issue is just a bad pressure reading.

[Brokenarrow]

um, oil... well, i found fully synthetic 15W50 Mobil1 on clearance for an excellent deal, so i used 3 quarts of that and and 3 quarts of conventional 5W20. so basically, im using partially synthetic 10W35.

That can't be good for your engine.

[fireguywtc]

What is your oil pressure like when at higher rpm's? My 352 had low oil pressure problems with almost no oil pressure at idle when warm. When I was going down the road it would be at 25psi or so about 2k rpm. my problem turned out to be the main bearings had gone out due to the crank coming foward and shearing of bearing material. I hope that you are not this unfortunate.

Here is my thread from long ago when I figured out what was wrong and tore it apart. http://www.fordification.com/forum/view ... =3&t=35513

[Thunderfoot]

im gonna try replacing the pressure sending unit. hopefully the issue is just a bad pressure reading.

I would try this first... I had this same type of problem with mine, the gauge read about in the center when I first started the motor then after it warmed up it went to zero... didn't change with RPM though... replaced the sending unit and now it is almost pegged when cold and about 3/4 after it is warmed up.

[BobbyFord]

Also, hook up a known-good mechanical gauge for an accurate reading. As far as the main jet in the oil galley goes, I've always run high volume pumps with no galley restriction and have never had an oil-starve issue. My 390 in my '63 shifts at 6,000 rpm's with no fluxuation in oil pressure.

[mad2smile]

have Holley 89 jets on order. also have bearings on order, but im hoping that isnt the issue. how hard is it to change bearings with the engine in the truck? there's no way in hell im gonna pull the engine again.

i just bought a tach and a mechanical oil pressure gauge. i hope they work well. they were from harbor freight. yeah, i know, i know. i shouldve bought some really nice ones. but hey, i had a gift card. why not try some crappy ones for free?

[BobbyFord]

Save yourself ALOT of hassle and pull the engine...

[mad2smile]

damn it. well, hope the gauges read what they should. i know it would be easy to work on the bearings out of the truck, but it was a bit of a pain in the ass getting it in there. heres hoping i dont have to mess with it.

[fireguywtc]

I agree with Bobbyford on this. You are going to make an hard task near impossible leaving the engine in the truck. You really need to get it out and on a stand to change bearings, other wise you will be on your back with the cross memeber in the way cussing like a sailor. Atleast I would in that situation.

[QC]

I don't think you are supposed to mix regular oil with full synthetic. I would change the oil and filter and see if the pressure is better before I over-hauled it.

[mad2smile]

i have it from a very reliable source who has been building engines for over 20 years that all oils, synthetic or not, will break down and blend together. not 100% sure its true, but he seems pretty knowledgeable about such things. i suppose i could run 6 quarts of 15W50, but im pretty sure my current blend will work.

[FORD428CJ]

You need to stick with one or the other. Conventional oil or synthetic! The seals on FE don't really like synthetic oil to well. They where never made for it. Also before you pull your engine, get a real reading on your oil pressure! Dont trust a dash guage at all. Also you cant order bearings for your engine until you look to see if your crank is undersized or not. JMHO

[averagef250]

Is the engine rattling like mad?

If you don't have oil pressure you'll frigging know it with an FE. If the valvetrain isn't clattering like mad then you have pressure.

Also, if you really do have a high volume pump and the bearings are bad to the point of showing no oil pressure you're going to need way more wok than just bearings. FE's run great and hold oil pressure with bearing clearance more than double the max limit of what they're supposed to be.

Something just smells half-assed about what's going on here. Nobody orders bearings before they get an engine apart and inspect it. You haven't even figured out what the problem is or if you have anything wrong to begin with. It also gets me that you haven't said anything about how loud the clattering is. Leaves me to suspect the engine's fine and you have a gauge issue. I've run FE's without an oil pump or oil in the engine and they are very, very loud.