Hi Everyone! I have problem with my silverado '99 5.3 vortec. I bought car few weeks ago and on begin oil pressure was jumping at gauge, but always enough high. Few days before oil change pressure starting going down, at idle sometimes to 0. After change oil Day by day was worst, in my shop the change oil pump (but dont change oring) pressure on new pump still was 0 at idle, today i change also oring on pick up tube (was broken) and on cold we got some pressure but still to low, on warm engine at idle going to 0 ... at 1000 rpm it is arround 20 psi and keep all the time 20-25 . Lifters heard a lot... someone have some ideas what need to check next? Also in pan was a lot of sludge and some magnetic iron stuff

 

Miles on engine, or KM's?

 

If the pan is still off, I'd suggest drop end cap of a push rod, with .020" plastigauge, reinstall, torque end cap. Remove end cap, and check bearing to journal clearance.

 

On clock is 128k Miles but I Think engine have more.
the pan is already reinstalled... Little late...

 

I'd say verify the oil pressure, but with you hearing lifters, probably low oil pressure. When not at idle, showing 20 pounds oil pressure, do you hear the lifter's? What type oil? You might try a heavier weight oil, as in 5w-40.