Hello, I just recently bought a '93 GMC Sierra from an 85 year old man. He bought it new and only put 100589 miles on it. About two weeks ago I was driving it and the oil pressure went from 48psi rapidly down to zero and back to 15psi. Later on in the day, It then changed to idling at zero to changing to 15psi going down the road and then all of a sudden jumping up to 30 psi. I have installed a new oil pressure sender, fuel filter, coolent temp sensor, plugs, wires, air filter, dist cap, rotor button, and new oil and filter as preventative maintenance and the gauge still acts funny. As of last Thursday I took it for a trip and the gauge hovers around 5 psi idling and rises to thirty when accelerating which is a big difference from the erratic behavior it was prior. I have also been experiencing a "hesitation or bogging down" when I lightly step on the throttle. It happens either from a standstill and also while cruising down the road in overdrive.

Could this be a faulty oil pump or a cam bearing?

I have two videos of the gauge behavior if needed and pictures of where the gauge was when I bought it.

Please advise.

V/r
Jeremy

 

It's hard to say what exactly it is without a tear down. If you're brave, try an oil pump. If you want to just go for it, pull the motor for inspection and new bearings. One thing you can check is crankshaft end play, it almost seems like the crank is walking back and forth on ya, causing intermittent oil pressure issues with the crankshaft bearings.

 

NullHead, Thanks for your reply. Do the Main bearings or Cam bearings generate oil pressure?

 

Camshaft bearings contribute to oil pressure, but most of the pressure that's generated from the oil pump is built up at the main crankshaft bearings.

Also, if you want to be 100% sure it's actually low oil pressure, you'll have to put an oil pressure gauge on it and verify the pressure. But either way, there's no way to tell if it's an oil pump or a crankshaft bearing issue. Gonna need to do some work to resolve it. No easy fix here.

 

its 22years old and tired. run a thicker viscosity oil and see it that helps.

 

Primem, what viscosity would you recommend?

 

Without seeing or hearing your truck. I would have to guess the same as what Nullhead said. You oil pump is on it's way out.

Be warned Jeremy5756 Every time your engine looses oil pressure, the top of your engine is not cooling or getting lubrication.

 

Is the truck knocking when the pressure drops off? Is it using oil? Is the oil milky when you check it? Have you changed the oil recently and has it had sludge in it?
The only reason I ask is because mine was doing all this and it was sludge build up from coolant getting into the motor. Within 500 hundred miles of an oil change my pressure would get noticeably lower...

 

timber74wolf, the truck is quiet when idiling. You can't even hear a lifter ping. It puffs a little smoke when it sits for awhile, which I think that could be the oil seeping past the valve seals. I forgot to mention that the truck sat for 1 1/2 years before I bought it. I have changed the oil and have a microgard filter and Castrol high mileage 5W-30. Could I have sludge on my oil pickup screen?

 

In2truk, once the weather gets better I'm going to drop the pan and change the pump. I'm all out of ideas..