Oil pressure gauge

I have a 1991 Mazda Miata. Recently I noticed the oil pressure gauge was vascillating wildly between 30 and 60, whereas it always stayed at 30 before. I checked the oil – it was fine. I took it to my nearby mechanic who said it was the oil pressure gauge. He replaced it with a Miata part (cost $350 because it was a rare year??). Now the oil pressure stays at 60 once I’m over 20 mph. So what is the correct oil pressure setting and do I need to take it back to the mechanic?
Thanks so much

I don’t know what the normal spec is for this engine, but if it behaves like it used to after the repair, it sounds like all is well and the correct part was replaced.

Have the engine oil pressure tested with a calibrated gauge by a good independent mechanic. If the readings match then you are good to go.

I’d post this on a Miata forum, find the oil pressure spec. I’d also have the pressure measured with a known good gauge. If it’s 60 and the spec is 60, fine, if it’s 60 and the spec is 30, then you may have a stuck pressure relief valve which needs to be fixed.

You are good. Sounds like the engine and oil pump are in good condition, 30psi at hot idle is great and 60psi running is not too much. Apparently this generation of Miatas has a lot of oil pressure gauge problems. The gauge is usually described as a “guess.” If you need confirmation, do what @missleman suggested and have a mechanic test it with a calibrated mechanical gauge.

The oil pressure specification for your engine is 43-57 PSI @ 3,000 RPM’s.