bad gauge????

i have a .030 over 454 and have a wierd problem. i have a 2 1/16 autometer mechanical oil pressure gauge on the front port on the engine. when you first start the engine in the morning, it will read 64 psi at idle. it will go up to 70 when warm and driving. but, if you shut it off, and start it right back up, it will read a diffrent reading. you watch the gauge and it will hard stop anywhere from 24-40 psi. when you rev it, it will not move. i ran another gauge to the other port on the engine, and that reads 60 psi hot at idle. i even tried a diffrent gauge in the same port as the original gauge, and it reads 60 psi. can this be a gauge problem, or would it make more sense to say there is a line problem? i use copper line for the gauge, not the plastic one that comes with the gauge. i checked the line for kinks or bends, and none to be found. i even tried to "bleed" the line at the gauge, but still this problem. the engine only has 75 miles on it, an the gauge has the same.any advice???

With the line all the way to the front of the engine, maybe just a bit of lag time for the oil to get all the way back to the gauge???? Don't the big block chebbies have an oil pressure port on the block at the back of the intake like an sbc has?????

no, it is above the oil filter, and on the front corner of the block. i thought about a lag, but i can start the engine, shut it off, immediately pull the line, install the other gauge, and it will read 60psi, when the other one read 24-40.

i forgot to mention, you can start the engine and watch the gauge go up and stop, like the needle is hitting something like a stop.this will vary pressure wise. i was wondering it there may be something in the line, and when oil pushes through it, it plugs at the gauge, not allowing the pressure to register .

i just dont know.....

Chuck the gauge. It has internal issues.

Mike - you may have something in the oil passage in the engine where you are attaching the tubing for the gauge. When shut down and cool, the debris settles. When you start up, the debris is pushed to the side of the passage and stays out of the way of the established flow path to the fitting/copper tube running to the gage. When you shut down warm, the debris is free to move in the warmer oil and may partially block the passage.

Have you removed the fitting from the block and checked for an obstruction? It doesn’t take much to restrict the flow to the flow/pressure to the gauge.

I’d also change the oil (warm) and see if that doesn’t take care of the problem.

Good luck on this,
Glenn