1988 chevy 4x4, oil press. problem

I have a high mileage 350 engine with low or no oil pressure. After the engine is fully warmed up the oil press. goes down from 30psi to 15psi and after operating the vehical for several miles the press. goes down to 0psi
at an idle.I was wondering if the oil pump could be the problem and if so can this be changed easily
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willy Since you state that the motor is high mileage its more likely that you have excess clearances due to wear. Worn rod, main and camshaft bearings are probably the culprit. Have you hooked up a mechanical gauge to verify your oil pressure?? You could add STP oil treatment or similar to increase the viscosity of your oil to buy you some time. I was always taught that due to the oil pump being the first to get oil and the last thing to run out that even though worn your pump will not likely be your problem. Russ
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rustynutgarage wrote:

    You never worked on many Buick V8's. They will eat a oil pump, and fill the gallies with a metallic sludge. Early 70's Buick 350's are the worst for this.
    Oil pumps do go south on Chevy V8's as well. Not as often, but it does happen. More often then not high mileage small blocks with low oil pressure are sludged up. I have pulled a number of valve covers to find a sludge layer so thick you can not find the rocker arms. I have pulled intakes and found the sludge so deep the entire lifter valley is filled to capacity. Charles
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Charles Bendig wrote:

PENSOIL is the Cause of the Sludge!

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Pensoil OR any motor oil that contains parifin (wax) but hey Charles! you just gotta try this.... change the oil on your SLUDGE machine with the filter and all, but dump 3 qrts of tranny fluid in the thing along with your 2 qrts of whatever. and run the thing for a good 500 miles. i did that one time i was suprized how well it worked. the only problim i had was draining the oil. the goo all collected in the bottem of the pan and i had to help it along with a screw driver. neat huh
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dirtdude wrote:

in the 70's we did 3 qts engine oil and one TRANNY .. Freed up lifters
you can also use 1 qt of Fuel oil But it makes your vehicle STINK !

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dirtdude wrote:

    Try this out. Pull the Valve Covers on ANY engine I own, in my personal vehicles. You will see NO Sludge.
    Why? I change my oil at my service intervals, I maintian my vehicles, I never buy cheep stuff to use on or in them. Guess that's why I can go 300,000 plus miles on anything I own. Neat Huh? Charles
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I have had to change the oil pressure sending unit twice on my 89 350. Is the engine making any lifter noise...you can't always trust the gauge. R

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rusty is right. your low oil pressure is from excess clearences, however.... i would hook up a mechanical gauge to verify oil pressure before doing anything, you can dump STP or somthing 'thick' but you will start to get 'deposits' if you use it all the time. if you determin you are indeed suffering from low oil pressure you can also change your oil pump to a high volume pump, the gears are 'taller' thuss moving more oil, you can also change the spring and plunger in the pump body so that you have more pressure. the thing to watch (listen) for is bad sounds, if you can hear your rods and mains when you put the motor under a load you are doomed, and a wrecking yard bottem end may be in order, you can also take your existing bottem end to a machine shop and have the crank ground .010 under rods and mains if you do most of the work your self you should be able to do it for under a hundred bucks.... plus gasgets
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Check your pressure with a mechical gauge... then run down to the parts store and get a new sending unit. It's a bell shaped thing that is screwed into the side of the block, just above the oil filter. It'll have one wire pluged into the top of it, and may have a blck heat shield over it. Not easy to get to, it's close to the fire wall. They fill up with crud after a time, and start sending the wrong info.
Been there... dun that.
Replacing the oil pump is a major, major job in a 4x4. you have to drop the front axel out of the way to get the oil pan off...
HDS
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