oil pressure

donb97 · April 19, 2004

I have an 88 chev 305 newly rebuilt. With a new oil pressure seng unit. When I start the vehicle I have no oil pressure. With no engine knock. So I guess oil pump is ok. but always after 10 minutes of running the truck either idling or down the highway, the oil pressure will come up and the red check gauges light will disappear.

What could be causing this ?

citydriver · April 19, 2004

Sounds like a bad sending unit,could be deffective.....however to be sure I would double check the oil pressure w/a mechanical guage......You might also wanna check the wire lead that goes to the sending unit to make sure it isnt rubbing on something it shouldnt be...

p.s....welcome to the site

2001 HD · April 19, 2004

If you have a gauge and a light, you may have 2 sensors. Not sure on an 88. Oil pressure switch and a sending unit. Switch is just an on/off signal to light. Sending unit is an analog transducer that will send a varible current to gauge. But for both of them to act up at the same time is unusual. You might also make sure your wiring is good and connectors fit tight.

Good time to invest in a service manual if you don't already have one. I agree with citydriver, verify with a mechanical gauge. Don't want turn burn up that freshly rebuilt engine. Could also be a weak oil pump if that one wasn't replaced during the rebuild. Isolate it to electrical or mechanical. If it's mechanical, looks like your going to need to drop the pan and inspect everything.

April 19, 2004

I'm with 2001HD. If you have a guage and a light you probably have a dual sending unit. It would be surprising if they both went out at once. It is possible that the cables could both be pinched.

Or,,,,,,this is an old engine, did you flush the block real good when rebuilding it? Suppose something got up behind the sending unit and it takes a while to push pressue up past it? I might take the sending unit out and check tha passage real good with a light (or have someone start the truck for a moment. Oil should squirt out pretty good right away). That'll tell you if the passage is clogged. (messy but it works)

Just a thought.