I bought a used 5.3ls motor. The other one blew up no oil pressure. I put a new oil pan without the relief valve in it, New pick up tube with o ring, new high volume oil pump, 5w30 oil. primed the new pump put a mechanical Guage so I could check the oil pressure at the port for the oil pressure sensor which i put a new screen in there as well. Still no oil pressure until I fired it up and reverse it up to 3000rpm then got 20psi but when let off the gas it drops to 0. I have been dealing with this issue for 4 months and we desperately need our tahoe back. Any suggestions would be appreciated. Thought about draining the oil for the 7th time and maybe putting in a thicker oil. I just need to figure out how to get oil pressure to the top of the motor. Also if I take my mechanical Guage off and turn it over oil does shoot out the top but I dint know why I can't get oil pressure it's got me stumped PLEASE HELP I have alot of money invested in this to blow it up again.

 

I could be something like drain back valve in the oil filter, might throw 10 bucks at it first.

 

we bought the new oil pan without the relief valve in it are you suggesting just a new oil filter

 

Yes. I am

 

Got any history on this used motor? How many miles; compresison test?
My high miles (350k) 5.7 cannot hold hot idle pressure over 5psi on 5/30; on 20/50 no problems 15psi