My 5.3 has 32K on a full rebuild. It runs great but its started doing this weird thing on cold mornings below 50*F. I'll start the truck, and the oil pressure will come up to 60 and then immediately fall backwards to 25 PSI. If I give it a little gas, the pressure comes right back to 60 but falls when it goes back to idle.

If I let it warm up, the oil pressure will come up to 60 and stay there. Then it's good for the drive, the pressures are right where they should be at cruise and idle. As long as the engine is warm, or the temp is above 50F, everything is good. But the first start on a cold morning, the idle pressure is low before the engine warms up. What gives? Is this oil pump or O-ring or what?

.002" on mains and rods with 5W30 synthetic and the 51522 oil filter. Melling M295 standard volume pump with high pressure spring.

 

I'm having the same issue in my lq9. Engine wasn't rebuilt but has a new melling oil pump like yours ~20-25k miles ago. I am not sure if it could be the sensor. When it goes to the lower side it tends to jump around a few psi. Goes right up to normal after a few minutes of driving.

Subscribing.

 

Checking pressure with a gauge or just off the dash? Could be a worn bearing that when it heats up is expanding and filling the gaps, could also be an o ring doing the same thing. Would put a gauge on it first, at the oil fiter and the oil pressure port, and see what you get.

 

Does it have that little filter under the oil pressure switch? My 09 tahoe did that until I removed the little screen but not sure if older trucks have that.

 

They didnt start that crap til the addition of afm/dod in 07!

 

Yea I ripped mine out and it was dirty as hell then after that I ditched the DOD

 

It was meant to keep the particles of crap out of the vlom, but creates more issues!