1981 Chevy 1/2ton, V8-305. High-oil pressure?

Question

When not started and sitting for more than 30 minutes, oil is at 40psi and engine starts with ease. After starting, runs at max psi, >60.
After shutting off, if oil psi not allowed to drop all the way back to it's resting psi of 40, the engine struggles before starting, like overcoming resistance.
Bought recently. Told it had head job recently. Can see new valve covers and seals, intake, oil pan, flywheel, master cylinder, alternator, wires and plugs.
Truck runs great, I can't find anything wrong with the truck inside or out aside from this.
Oil condition was good, but it had about 1 1/2 quarts over full. I changed oil and filter and filled to correct levels. Same issue.
I'm worried I'm going to blow my seals if the oil-pressure stays this high.
Any information or insight will be greatly appreciated.

Answer 1

There is also a bypass (relief valve) in the oil filter mount (where it bolts to the block) between the Oil Pump and the valve just mentioned would guess your problem to be in there. Once the motor is shut off, turn the key back on (key on engine off) your oil pressure SHOULD drop to zero. IF it does NOT, then your problem should be as described.
IF it DOES drop to zero and you still have a hard start then that is not your problem (obviously).

1981 is a Carb Model with HEI distributor / if your hard start comes after a shutdown, but quick restart (10 - 20 minutes) - then what is more than likely happening is your CARB is running RICH and your timing is a touch too ADVANCED - this makes even more sense if the motor just had work done, timing was set sloppy, and now it is summer (more heat for the head, harder restart problem) - reduce the mixture and make SURE your timing is near normal (you CAN set it by ear but in summer you back off a bit on the timing) ALSO make sure your vacuum advance is tied to a PORTED vacuum source (IE: make sure there is NO vacuum on the hose when the motor is at idle)

Answer 2

The oil pressure sounds normal. It should be 60 at cold startup and 40 when warm. The pressure should be higher when the oil is cool, it has more viscosity then. Do not worry about the oil pressure, that is not your problem. The hard start when the engine is hot is a timing problem. The timing is advanced too high. Have the timing checked, or check it yourself with a timing light, and set it back to base timing of 8 degrees before TDC. Someone may have bumped up the timing trying to get more power out of the engine, but caused a hard start concern instead.

Answer 3

Sounds like the relief valve in the oil pump is stuck open. Also in that year there were 2 oil pressure switches a 80 psi and a 60 psi. So it might be good to just replace it with a new one as a first step. If the proper psi switch does not fix it then sounds like a new oil pump.

Answer 4

Let me understand this correctly!!...you said when "not started
and sitting for more than 30 minutes the oil is at 40#......
.
The Oil is at 40 # with the engine off??...and when you start it
its at 60#..???

I'm assuming you have "GM gauges in your vehicle, as I do
( I have a 1979 Chevy 1/2 ton 4X4 pickup w/350 engine

I think as our vehicles "age"...the gauges get way off track, both my oil and temperature gauge are way off.......

If you want an accurate picture of your Oil pressure get a good
"Mechanical" Oil pressure gauge, the kind that you use a fine Nylon/or copper tube to a oil pressure line.....

I'm glad you found the problem of the oil being "Overfilled" that could lead to blown oil seals and who knows what other problems....

I'm hoping I was of help!!!


..Richard...Reno, Nevada

Answer 5

it sounds like it has been rebuilt,,if they put a high volume oil pump in it,,this will make it have high oil pressure all the time,,some people like a lot of oil pressure,,but i don't,,it blows seals and gaskets,,i own a repair shop,,and don't recommend using these pumps,,you can try bleeding the line,,it may have air in it,,and be giving false readings,,but if you bleed it,,and it still runs high,,it probably has a high volume pump in it,,you can take it out,,and put a regular pump in it,,i know if was mine i would,,any way good luck with it,,i hope this helps.

Answer 6

replace oil sending unit and retard the timing a lil bit
dont worry about oil pressure on a new motor till it goes 80+
then you have a problem washes bearings out =not good

Answer 7

It sounds like the gauge is bad because there should be NO pressure when the motor is not running.