I have a 99 silverado the 5.3 and the oil pressure will stay at 40 at start up, but once he truck warms up it will drop to about 20-25. And will jump up and down from there unless I'm moving. In that case it will stay at 40-50. Any reason it would do that? Oil levels good and just did an oil change.

 

Was it doing it prior to the oil change??? May be a bad or wrong filter. How many miles on the truck??

 

Before the oil change it was doing the same thing except a little worse. At start up it would sit below 40, and once it warmed up it would drop to 20 again. There's 287,000 miles on it.

 

Sounds like time for a rebuild... Or at very least oil pump and some bearings.....my 5.3 was doing basically same thing youre describing, except it would knock for about 10-15 seconds when i first started it up... Especially on really cold mornings....oil pump went out with my 4 kids in truck about 45 minutes in on a 5.5 hour trip back from my moms.... Was half an hour from dropping kids off at my exes when first two rods let loose.... Sadly i drove it onto the wrecker, off the wrecker onto my buddys trailer, off the trailer at his house and 2 months later when i started pulling the truck apart for engine swap/mods/paint i hit my remote start and drove her into his garage.....

 

I wouldn't be surprised if the o-ring on the pump/pick-up tube is not sealing that great.

If no know knocking or anything else, it seems that the motor is just fine.

If you looked up specs, you should still be within spec. 40 cold and 25-30 hot idle is more than enough to keep everything oiled. And driving around 40-50 is fine aswell.

If anything you could pump in a new pump/o-ring and see what it does.

Or just run a thicker oil like I did on my sierra that had 250k+ on it.

 

Thanks. Will do!

 

what weight did you change it to, to give it some more pressure? im using 5w30 right now.

 

In the non winter months I went to a 10W40, it still ran great.

My main issue was oil pressure when in really cold weather for a first few minutes, I think when the o-ring got warmer as the engine did it sealed up better and all oil pressure was back to normal. I did run a thinner oil in the winter but the thicker oil in the summer time got me like another 5 psi atleast.

 

Did you use 5w30 in the winter then?