Reson for low oil pressure on gauge

On my '88 Formula 350 the oil pressure gauge stays below 15 psi when driving engine warm, and like 5 psi at idle. I don't know if the gauge is off, or if it's really that low. There's 133k on the engine, it doesn't smoke or leak oil anywhere. I'm semi-worried about it actually being accurate and my engine seizing. Is this a common thing or what? Any way to test oil pressure?

Your oil sending unit or the oil gauge is probably a big fat liar. If your oil pressure was that bad you would be having way more obvious problems besides a lying gauge. I would go out and buy a new sending unit and if it still says that go out and buy one of those little 10 dollar aftermarket oil gauges to hook up and see what it says.

Good luck man. Hopefully its lying to you.

My 92 had 5psi at idle...and then I spun a bearing! lol Definitely check that out!!

Go to the auto parts store and get one of the cheap mechanical oil gauges. Remove your sender and put the connection for the gauge's line there. The gauge should come with enough line so you can run it up around and in through the driver's window. Tape it where you can see it and take the car for a short drive to see what the pressure is like.
If it is still low you'll need to replace the oil pump. And if a new pump doesn't raise the pressure, then you have excessive bearing clearances and need to have the engine rebuilt.

with 133k miles i dont think it would be that low. Plus 5 PSI would have the motor running poorly and making lifter noise. But definatly something to check out. If your not hearing internal engine noise i wouldnt be too worried until you know for a fact what the pressure is.

Yeah there's no knocking/ticking going on, sounds smooth as new. The oil sending unit is the thing right above the oil filter with the plug going into it correct? (oil pressure sensor?) If so, that's brand new. I'll try what Morley said with the mechanical gauge, sounds simple enough. Thanks!

When you changed the sending unit, did you use a factory unit or an aftermarket one? If its an aftermarket one, try changing it with a factory one, when I changed the unit on my grand am, the aftermarket one didn't read pressure accurately, kept tripping the light for low pressure, but the dealer unit worked ok, and the gauge almost matched the mechanical gauge I tested it with.