Need4Camaro

iTrader: (1)

This is on a just built new 5.3 LS FBody style motor, the oil pump came from another "new" motor but that motor had water damage and rusted over. The pump was cleaned but here is what happens.

The pressure goes right up to 60 PSI on startup, then slowly the pressure lowers down to nearly the red mark as the car warms up. What is causing this?

Camaro9969

iTrader: (12)

What type of oil are you running? See if you can get a real gauge on there somewhere to see the actual pressure

Need4Camaro

iTrader: (1)

Mobil 1 Synthetic 5w30 - I have heard Mobil 1 runs thin but I dont think it should have the viscocity of water. No real pressure gauges on hand right now, do you happen to know what could cause this symptom though?

Undertow74

iTrader: (45)

Is the o ring good on the pump and the pickup tube tighten down good? Or mabe that "new" used pump is bad

fruitsalad

iTrader: (5)

Sounds like it could be a bad pressure relief spring sticking open and bleeding pressure off gradually, especially if the pump came off a motor with water damage.

Is it 60 psi at warm start too, then bleeds down, or only at cold start?

Need4Camaro

iTrader: (1)

According to the shop they used a new O-Ring and made sure the pickup was tight. They say they highly doubt its the pump though.

LilJayV10

iTrader: (39)

I had the exact same thing after my head/cam swap. It was the oil pressure sending unit. I'd never seen one fail like that.

02ElectronZ06

yeah I would check the sending unit. I had a bad sending unit. Car would fire up and run fine for a little while but pressure would drop after a WOT hit or two.

elizaharry

My guess is, it is something plugging your oil pressure sensor. Try filling with oil to a level above the point where the oil pick-up tube meets the case, see if there's a difference.