2 350 same problem

[84Distefano]

Hello,

Kinda stumped with my 84 C20. I had the original motor lodge a rod or two. stopped the motor dead. prior to this issue i noticed the oil pressure wasnt consistent and tended to be kinda low. never electrically irratic but it was run low. at 40-60(after being fully warmed) would hang around 30-40 psi but coming to a stop or at idle would hang around 10-15 psi. i swapped in another 350 and it is having a similiar problem only a little more severe. it drops off the oil gauge at stop now. at idle it sits between 9-12 psi. and seems to respond better under normal driving conditions, sitting somewhere around 40-45 usually. there is some "rapping/ticking/slapping" that sounds to me like valves but at idle sounds like rod knock a little. doesnt do the "rod knock" all the time just after a 30 minute drive. and only at idle. the other sound does it if i hold a constant rpm/speed. any ideas?

Thanks for your time.

 

[nvrenuf]

What was the mileage of the first motor?

Was the 2nd motor new or used? If used, approx milage? Low oil pressure + internal noise tends to indicate it's a P.O.S..

Electrical or mechanical gauge? If electrical, verify readings with a cheap mechanical gauge.

 

[bucket]

Is there an oil cooler on the truck? I suppose it could be clogged causing oil flow issues.

But it does sound like you installed a worn out engine.

 

[89Suburban]

Yikes.

 

[84Distefano]

first motor had around 121k and slowly lost pressure over a short period of time. and the second motor i was told had 8000 miles. seems like valve tick at first when holding constant speed. after running for 30 min or more and sitting at idle afterwards it has a low in decibel knock it seems.

 

[84Distefano]

the gauge is the stock that came with the truck and stock sensor. i would imagine that it is the mechanical. it has a mechanical pump with a pressure switch.

 

[dhamp]

Can't really trust the stock oil gauge in the dash all the time. I can tap my dash 5x and get a different reading every time.