tech2

sounds like the engine bearing clearances are excessive...worn out tired motor. only way to know for sure...is a tear down. I'd run the heavy oil until it gives up and find a new motor.

SimpleHauler

That's what I was thinking. Even at 30 years old the body is solid and many other new parts were installed. Definitely worth a 350 crate motor.

Rednucleus

My 93 with 350k mi has done this for about 100k miles now. At operating temp at idle 5psi, 15-20 on the highway. Changing to 20-50 oil increased readings by 10psi.
Could this also be a bad sender or gauge problem??

SimpleHauler

Thanks for reply. The pressure slowly drops to zero or perhaps 1-2 psi (gauge is not graduated so accurately), but never increases once motor has reached operating temp. I assume the oil is still pumping at some pressure somewhere. I'm going to try an oil change to 20/50W tomorrow, I'm pretty sure the gauge works ok but who knows??? I'll drive it and take my chances. A rebuilt crate motor is still cheaper than any used truck that I see for sale. An after market oil pressure gauge may be worth the cost and trouble to install.

kevinkpk

Low oil pressure with proper viscosity oil, and properly functioning oil pump is indicative of excessive bearing clearances as Tech2 states. When/if you tear down the engine, you can mic the journals, and bearing caps, that will tell you the clearance.

SimpleHauler

Thanks Kevinkpk, I will replace this 305 with a 350 at some point. Not sure how long I can drive this as is but I'm gonna take my chances. I installed 5 qt 20W50 and pressure is slightly better but ultimately gauge pressure is dropping to zero. Any idea on how far I might go before motor noises begin? Nice Olds by the way. Reminds me of a 71 skylark I owned-green with a black vinyl top with a black interior-rust free around back window. Back then they were just everyday vehicles. I could retire early if I had all the vehicles I once owned!

Suburban Dude

As soon as you save enough money, might as well get the 350 installed. It will get you another 200,000 miles. GM makes a nice 350 crate engine for a reasonable price. All brand new.

If you want to keep going with the old one it might last a long time or it might spin a bearing on the interstate at night and you might get to meet whole new bunch of “friends”. LOL

SD