Oil Pressure's a bitch

I pulled an old merc out of a field its been in since 1992 . It's got a 390FE with 120k that I got running strong and doesnt smoke a bit. When I start the motor cold it has about 50psi of oil pressure. When the motor is at normal operating temperature it has 0psi at idle and 20-30psi when driving. When it has no pressure at idle the motor does not knock or tick at all. I put a new oil pump and pick up tube and screen a couple weeks ago with no result. For ****s an giggles I ran sea-foam and Marvals Mystery Oil through the oil with no results. Im am currently running a quart of lucas oil stabilizer as I have heard good things about it but have had no result. I checked the gauge and it is fine. Is there something I am missing? Is the motor just sloppy? Am I a retard? Should I just run her til she blows? Any tips wouild be much appreciated.

 

check it with a different guage

 

Already did. no luck. well... no good luck anyways

 

Cheap gauges will confuse you sometimes. Verify with a diagnostic gauge.

 

what kinda oil you runnin also?

 

Check it with another mechanical oil pressure gauge. If the readings are the same, Id say the 390 is in need of some new bearings. Could the low pressure be the reason it was parked? With that many miles on it Im sure it needs a rebuild.

 

I had the same symptoms with improper cam bearings on a SBC. Not sure if it could cause the issue with an FE, but if you are using a good hydraulic/mechanical gauge, you can trust what you are seeing. If it is an electrical sender type gauge, don't trust it--maybe a bad ground or bad sender. Cut open your oil filter and see if there is metal in it, or pay for an oil ****ysis.

It could possibly be your oil pump too.

 

i'm running 10-40

 

try a direct hook up mechanical gauge. if it stays the same its rebuild time.

 

if you are looking at a factory gauge there could be crud in the line or it could be kinked or something. hook a good mechanical gauge right to the motor, and check it there. do those engines have a byp*** valve where the oil filter attaches? it could be frozen in place or something. could have stuck partly open and made the oil pressure lower then it should be,causing it to be parked. actually come to think of it is it the filter that was on the car? ,i hope not,but if it is get a new filter. filter byp*** could have deteriorated

 

I would bet it needs rods and main . Had a 390 that did the same 0 oil psi when warm no noises. Pulled the pan found all bearings down to br*** slipped in some new inserts and she was fine.

 

could also try running more viscous oil (20/50) should get better oil pressure

 

If it doesnt knock .dont worry about it.Pull a valve cover and check. My pontiac has 0 oil pressure at idle.Its the guage When I give it gas it climbs fast with just a touch of throttle.Been on the road for 2 years. As long as oil is getting through to the push rods your fine.My 2 cents run it ..........

 

My .02 ,worn mains.

 

I would think if it had zero oil pressure the lifters would be rattlin' like crazy .. ??

 

Don't any of you guys READ before posting? He said he put in a new pump and screen. HELLO...........ANYONE READ (or understand)ENGLISH?

Frank

 

that gauge could be off ten pounds easy, + - ten psi full scale isn't uncommon. get a good test gauge straight off the block and i bet you have pressure at idle.

 

I had goofy oil pressure readings on my Pontiac motor but it ran fine, right up until the main bearings locked up...go get yourself rod and main bearings and a gasket set...God knows what's in that oil pan...case in point, my Poncho oil pan was filled with rocks, sticks and mud after 3 fresh oil changes...take the pan off and save your motor's life...

 

well he needs to verify the actual pressure first, then go from there,that would be the best thing before tearing the engine down.

 

I'd vote for mains and rods as well, had a olds engine that did the exact same thing.

 

weak at idle with new pump = worn mains and rods

 

ok, simple. as said: "worn bearings, mains and rods , also...thrust surface on mains.

Hook up a electric pump to where the oil pump attaches and pump kerosine through it. leave off the pan and you can verify visually where it leaks worse...Smokey stlye...LOL

 

Also, if you have ever flooded the engine to the point that gas washed past the rings and contaminated the oil in the crankcase (easy way to check, just smell the oil on the dipstick), that could be the problem. Oil contaminated with gasoline will cause the symptoms you describe.

 

Cam bearings ...

 

before anyone tears this motor apart, verify the actual oil pressure with an accurate mechanical gauge.

 

Run it. I've been around a lot of old stuff that didn't appear to make pressure at idle but didn't knock or tick.

Realistically, if hydraulic lifters aren't ticking, you're making a couple psi whether or not the gauge shows it.

If you have a fram filter on any engine with oil pressure issues replace it immediately with another brand. Seriously

good luck

 

My 350 Chev motor started loosing oil presure all of a sudden last month, it wasn't rattling and the lifters were fine, it dropped to zero at idle when hot. I went to 20w50 oil and it still didn't change. All it needed was the oil pressure sending unit and now we have good readings at the gauge. I agree with the majority, you may need lower bearings if still no pressure after machanical gauge doesn't show the problem.

 

Your cam is oiled first with the FE. When the cam bearings are sloppy, the oil spills out fast through them resulting in low oil pressure at idle. Does it raise as soon as the RPMs come up a bit? If so, that's going to be a factor. A high volume oil pump may help for the short term, but low pressure on an FE is going to require work and a few parts. And while you're in there, you may as well...............

 

EXACTLY! As I was reading exactly what I was going to type.

If not ticking you're getting something.....like all the rest said, unscrew the gauge or sender unit, and screw in a diagnostic gauge. If no access to a high dollar tester, buy a mechanical gauge (less than $20 at Oriellys) but use the shortest amount of that small hose as possible.

The filter. Swap it. Just two months ago, I had a just put my race motor back together for a big race in SoCal. 1st start on it, oil pressure went to 40psi as usual then bleed right to 0 in about 3 minutes. Shut down, brainstorm, go though 36 hours of tear down, rebuild, new oil pump, total inspection. Once everything was fine we started thinking packing peanut or something in an oil p***age. Blew all those out. Everything check out better than FINE. Put back together, put back in car, it does it again. 40 psi then bleeds to 0psi. Just before tossing the motor for the backup we swapped the filter. M*(^*&%($ filter, brand new out of the box had a bad checkvalve and was locked shut. And let say I dont run cheap **** on my race motor.

We would have saved a day and a half and a night of no sleep had we swapped that filter straight away.

 

Does that engine have a pressure byp*** valve in the filter or the engine? If in the engine that could be the problem.