351 Oil Pressure Problem
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New User
Joined: Jul 2004
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351 Oil Pressure Problem
Whenever the engine get warmed up my oil pressure slowly goes down until eventually it will drop out. Especially when at an idle. I am looking to sell it soon. Just wanting to fix before I sell.
Junior User
Joined: Jul 2003
Posts: 72
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From: Florida
You could try putting a new oil pressure sending unit on. It is a cheap and easy fix. It would be nice if that was your only problem. I have had several go bad over the years.
On the other hand. Your main bearings might be wearing out. I have this problem now. I put in 20w50 oil and some Lucas oil treatment. Now the pressure stays up much better.
On the other hand. Your main bearings might be wearing out. I have this problem now. I put in 20w50 oil and some Lucas oil treatment. Now the pressure stays up much better.
Mountain Pass
Joined: Jun 2003
Posts: 203
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From: Killeen Texas
I had similar problems with my 90 302. I tried a new pressure sensor but the rod and main bearings were worn out. You can always get a mechanical gauge and hook it up where the oil sensor is in the block to check actual oil pressure. Thats what i did before rebuilding the engine.
5th Wheeling
Joined: Apr 2004
Posts: 26
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you might want to check what is in the oil pan. i a truck that i bought a few years ago i started having a problem like yours and it ended up being the wrong oil was used in the motor or it was not changed by the guy who previously owned the truck. since this was not done the oil created a hard crusty material that would clog the p/u screen every once in a while but in high rpm's it would completely clog up and loose oil pressure. eventually the mat. completely clogged it up. (it progressivly got worse).
if i rember right though if bearing are bad as you give it gas then the oil pressure will drop not at idle unless bearings are really bad.
if i rember right though if bearing are bad as you give it gas then the oil pressure will drop not at idle unless bearings are really bad.
5th Wheeling
Joined: Apr 2004
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i can bet money that there i some crud in the pan clogging up the screen. if it would be the bearings there would be also a knock in the motor. also to does the motor knock when pressure drops at idle? I forgot to ask you that before. if it does not knock it would be the sending unit.
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Lead Driver
Joined: Feb 2003
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From: Oak Harbor, OH
There might not be a knock, my '82 351 would have no pressure at idle, but it would when you started moving, it had a bad wrist pin, but the bearings didn't male noise.
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5th Wheeling
Joined: Apr 2004
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but a bad wrist pin would not cause you to loose oil pressure. the reason why you would get a knock when you started moving was because you put a load on the piston when you started to move. if the bearings make a noise they have spun in the rods or mains. if the lifters knock then the oil pump is not working because they are after the oil pump not the bearings. he just needs to listen to the motor if it knocks, is it deep in the motor or in the top
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New User
Joined: Jul 2004
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It does have a knock when the pressure drops out. Sounds like it is on top. But as soon as I step on the gas it stops. It has happened before, I been driving down the highway and all of a sudden the pressure drops completely out. I pull over, shut the truck off and restart it and I get pressure again.
5th Wheeling
Joined: Apr 2004
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it sounds like mine did. there is some crudd in the oil pan and it needs to be cleaned out and pull the p/u tube and clean it or replace it. if you caught it early enough there might not be any damage to the motor yet. it sounds like this is a lot of work but it will probibly take a couple of hours to do the job your self if you have some good cleaner and a new oil pan gasket. as you step on the gas the lifters get enough oil through the crud. while you are driving down the highway it drops because you start sucking the crud from the bottom of the pan and it cloggs up the p/u tube and it all falls to the bottom of the pan when you kill the engine and it has oil to suck up.
good luck.
good luck.
Post Fiend
Joined: Nov 2001
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From: Topsfield, MA
It should be between 40-60PSI when warm at idle. If it's between 40-60 when cold, and then drops once the oil warms up, than your engine is wearing out and will soon need a rebuild. If you drop down to 0 psi, that rebuild is around the corner. The bearings/races etc etc as they get warn, create gaps/spaces that cause the oil to loose it's pressure. It only happens when the oil is warm because when it is warm, it is thinner than when it's cold. You can try some thicker oil or some of that Restore stuff, but other then that, rebuild time.
Lead Driver
Joined: Feb 2003
Posts: 8,140
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From: Oak Harbor, OH
What I said was that my main bearings were indeed toast, however they did not knock, it was the wrist pin that knocked, and the bearing did knock right before I traded it in, they were knockin at 45mph while holdin 35 psi of oil pressrue.
5th Wheeling
Joined: Apr 2004
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not nessarily so because i got another 40,000 mi out of my motor until the crud fell off of the lifter inspection cover and callopsed all of my lifters. when i pulled the motor the bearings had the same amount of wear that any motor would have that had 150,000 miles on it or even when i would run 1-2 laps around a track with no oil pressure.
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Nov 1, 2004 11:08 PM