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OT/Chevy 350

A

Anonymous-0

Well-known Member
Hi guys,
I have a I have a 350 in my Chevy pick-up. I am having oil pressure problems. We got the truck free from father-in law who passed away. So we don't know much history on it. This winter we would get 15 lbs pressure at start up then once warm it would drop to absolute 0. I did some reading and replaced the oil pressure sending unit. I think that is what it was called. I then started the pick-up and drove it for a long time and it held 15 lbs of pressure. A week later no oil pressure again. A while later I changed the oil to 15w 40 and also filter. I had 50 lbs of pressure cold then would drop to 15 lbs at warm up. Now it is at 50 lbs at start up then drops to zero at warm up. Can anyone suggest any direction to go. Is it likely the engine is shot? Thanks for any and all help. Sorry for the long post
 
drop the oil pan and check the mains and rod bearings, it may also have spun a cam bearing. if it sat for a long time the bearngs could have been dry and spun at start up. look for any signs of metal in the oil, check the drain plug if its magnetic for shavings.
 
What year? Any noises, such as the lifters getting a little noisier than usual at low oil pressure?
 
Agreed.

You might check the sending unit again. If the oil galleys are horribly dirty it could be have already filled with gunk.

It seems strange that you got oil pressure back then lost it again after a little use.
 
My son's Ford did that. The composite timing chain came apart. It would run a mile or so and then stop up the oil pick up screen.
 
How are you checking the oil pressure? You can't
trust the factory gauges.Check the oil preesure at the block with a good gauge.
 
first thing to do is check the pressure at the block with a manual guage. AND if it was dropping to zero that many times that motor would not still be running.this test will tell the story and then go from there. no sense pulling things apart till you know where the problem lies. can pretty much rule out a spun rod brg. as you would definitly hear it knocking. at o psi you would have a lot of lifter noise. worn brgs will cause some drop in pressure once oil is warmed up but to zero is probably unlikley. problem may also be in oil pump, relief valve, guage, sending unit,wiring.
 
You don't give much information like year of truck or mileage.
But let's just step back a little. You got the truck for $0 and you say nothing about the body so I am presuming that it is good (no rust particularly holes). The engine is running and as Rustred said if it really had zreo oil pressure it wouldn't be. Maybe there are a lot of miles and the bearings are worn. So the motor needs to be rebuilt which means you need some bearings, rings and gaskets and some machine-shop work. That motor should be rebuildable for under $2000. AND you got it for nothing so that is all you would have in it.
Pretty cheap truck.
 
Possibly a worn oil pump. Cold thicker oil will pump and build pressure but when it warms up the oil thins and the pump with its excessive tolerances can no longer build pressure.
 
i agree, put a mechanical gauge on it to see what the warm oil pressure really is.

If the pressure really is that low when warm, with no unusual bearing noises, I would first look at checking / replacing the oil pump.
I have had the oil pressure relief valve spring in the oil pump break and give low pressure like that.
Those distributor driven pumps used to sell for only $25, so is more work than money to change it.
 
if your motor winds up needing an overhaul, you can get a gm goodwrench 350 crate motor from jegs performance, its a long block, transfer your intake and ignition system over to it for 1799.99. a lot less hassle than doing the rebuild. jegs.com
 
On the older small block chevys that most often is a sign of mains getting worne out.
I would want to run a good presure gage on it first.
 
when engine warms up and pressure drops,shut engine off and check oil...i've seen engines sludged up on top of heads and oil pools up top...let it sit awhile and it runs back down to pan.
 
If it has a lot of miles, which I'm assuming it does if it's a 350. Depending on its service history, I'd say the ole girl is tired. The best way to check is use a direct pressure gage at the sending unit port. If your still getting 15lbs or less oil pressure after its warmed up, the ole girl needs a rebuild. The cam and main bearings are probably shot.
 
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