Help! 1981 Oil Pressure Assist Please

[FactoryC3]

I have a 1981 Corvette. Factory stock. 23,000 true miles.

I have had a continuing problem with the oil pressure reading on my car.
The problem is that when I first start the engine to idle, the pressure gauge reads a bit below 20. After about 5 minutes, it pops up to just below 40, on its own, at the same rpm. If the rpm is revved, it moves slightly, but not much (2-3#).

With the ignition on, the gauge will peg to 80 with the connector off and grounded, and return to zero when not grounded.

I changed the sender with a 33641 sender from Wilcox. Tape only on first 3 threads so ground should be there.

I replaced the jumper wire from the harness to the sender with a 29495, also from Wilcox.

I cleaned the male connector on the harness.

There was no change in the readings and all previous tests returned with the same results.

I read every post I could find, but none hit the nail on the head.
Could someone head me in the right direction?

 

[Antz81]

Have you checked the pressure with a mechanical guage?

 

[toobroketoretire]

While all this is going on what does your volt meter indicate? If your alternator isn't charging at first it'll give a low oil pressure gauge reading UNTIL it starts charging. Make sure your alternator belt is properly tensioned and with no signs of oil on it. The alternator has a side plugin with two wires; a large constant HOT and the other smaller HOT only when the key is turned ON. It's very common for the little wire (a single strand wire) to break inside of it's insulation and then make contact once in a while. You can test that wire by turning the key ON, use a battery powered test light stuck into the terminal, then bend/pull/push the wire and see if it stays HOT (it should). And don't forget to plug the plugin back in after you test it.

Are you absolutely sure it only has 23,000 miles and not 123,000 miles? If any of the 6 u-joints have grease zerks in them it almost certainly has 123,000 miles because the OEM u-joints didn't have grease zerks. And it would most likely have the original belts and hoses too. And the alternator would have it's original number stamped into the case along with it's amp rating. Very few 36 year old cars with REAL low mileage are on the highways now days.

 

[LLC5]

I have a 1981 Corvette. Factory stock. 23,000 true miles.

I have had a continuing problem with the oil pressure reading on my car.
The problem is that when I first start the engine to idle, the pressure gauge reads a bit below 20. After about 5 minutes, it pops up to just below 40, on its own, at the same rpm. If the rpm is revved, it moves slightly, but not much (2-3#).

With the ignition on, the gauge will peg to 80 with the connector off and grounded, and return to zero when not grounded.

I changed the sender with a 33641 sender from Wilcox. Tape only on first 3 threads so ground should be there.

I replaced the jumper wire from the harness to the sender with a 29495, also from Wilcox.

I cleaned the male connector on the harness.

There was no change in the readings and all previous tests returned with the same results.

I read every post I could find, but none hit the nail on the head.
Could someone head me in the right direction?

Start with Antz81 recommendations, you need to know that the oil pressure is good first, diagnosis 101.

I have seen the wrong oil and/or oil filter cause issues like this also. Has an oil change been done recently?

 

[FactoryC3]

It is 23,000

Are you absolutely sure it only has 23,000 miles and not 123,000 miles? If any of the 6 u-joints have grease zerks in them it almost certainly has 123,000 miles because the OEM u-joints didn't have grease zerks. And it would most likely have the original belts and hoses too. And the alternator would have it's original number stamped into the case along with it's amp rating. Very few 36 year old cars with REAL low mileage are on the highways now days.

More than you think...
Previous owner had car for over 30 years and put only slightly over 1000 miles on it. All data backed up titling and registration info. Milage documented. All numbers matching (including alternator). No zurk fitting on universals. Original hoses had to be replaced as did the belts. Even had the original factory tires on-board. Good tread but dried out around the beads. Still had small rubber nibs on tires. Take a look at my album. Had original plugs in engine. Was "Bone Original". Truely...