I have recently acquired a 2006 Silverado 1500 4WD with 5.3 V8 and about 250K miles.
When the engine is cold, I crank it up, and rather shortly the oil pressure will go to zero unless I keep the RPMs up to around 800. It seems to idle around 500 RPMs. As I drive around, come to a red light or something, if I don't keep the RPMs up, the oil pressure will go back to zero. With the RPM's up, it runs between 30 and 40, depending on the RPM.
Now once the motor gets up to operating temp, this all goes away and the oil pressure won't drop below 30.
I've had the oil changed, several times, tried 10W/30 and 10W/40, I have had the oil pressure sending unit changed out, have tried Sea Foam in the oil between changes, etc nothing seems to change this condition when the engine is cold. I've talked to two repair shops, they both say that it's not the oil pump since it's working when the engine is warm, but they are not sure what it is. One is recommending I change out the engine or have it rebuilt.

What's your thoughts on what may be causing this. It seems to be puzzling everyone that it only happens when the engine is cold, once up to operating temp, it runs fine.

Thanks,
Richard

 

Is your Chevy making any kind of unusual noises when the oil pressure shows 0 PSI on the dash?

 

Yes, the lifters start tapping. So the oil pressure is actually dropping, not just the sending unit being bad.

 

Points to me anyway, partially plugged oil passages. Try some treatment for oil. Back in the olden days, we'd mix a little diesel with oil.

 

Sounds like a oil pressure relief valve issue in the pump. Have you had the oil pan off to see if the screen is blocked or if the o-ring is bad?

 

No, its my mom's truck, I'm just using it for a bit, but know some of its history. Next time its due for an oil change, I'll take a look at popping the oil pan off and looking at it. What should I be looking for on the O-Ring?

 

Some people swear by Marvel Mystery Oil. I've never used it myself. CD-2 seemed to help one motor I was working on. Some people swear by a quart of ATF along with motor oil.

Was rebuilding a 1965 Ford 289 out of a Mustang. Most all the push rods were carboned up like mad inside. Had to throw those out. I'm surprised the car was still running.

Original owner must have been on the 25,000 mile to 50,000 mile motor oil change plan.