I have acquired a '93 with 91,000 miles that had been sitting for ~5 years without running. After new plugs/wires/fluids and putting some oil into the rotor housings and turning the engine over by hand, she fired right up.

I noticed the oil pressure was reading almost zero once it was warmed up an idling. I drove it around the block (old cracked tires and very rusty rotors so I didn't go far OR fast) and watched the gauge climb to maybe 30-40 psi at higher RPM (about 4500 if I recall).

Is this normal?

 

The gauge doesn't work. Don't rely on the gauge. It's trash from the factory. Whatever reading it's giving you is wrong. So it's normal for the gauge to not work

 

I have to disagree cr-rex. I think the gauge is probably fine. It's common on the FD to have low indicated oil pressure readings, especially as he's described...at hot idle. OP, the oil pressure sender is located on the left side of the engine just under the oil filter pedestal and has a single spade connection. That connection can get fouled over time from oil dripping down during changes. At idle the signal is weakest and can't get through that connection. That results in low indicated pressure. The sender can also go bad, but I'd clean and tighten that connection and see what you get.

 

I agree that the gauge can be made to to "work" but it's reliability and accuracy has been shown to be that of the water temp gauge. If monitoring oil pressure is important to you, as it it is to me, an aftermarket gauge is the best solution. You can even fit it in place of the factory gauge and sensor.

 

But the oil pressure gauge isn't like the water temp gauge at all. The temp gauge isn't linear and I agree, should not be relied upon. But while you could argue the oil gauge doesn't have enough resolution (i.e. can tell you your pressure is exactly 55 psi.) it IS linear. And IMO you don't need a high resolution oil gauge in a street car. Pressure fluctuates so quickly (way faster than temp would) that's it's not of much use. After a week or two each owner will know what's normal at a glance for HIS car depending on rpm, oil viscosity being used, engine temp etc. He doesn't need to know that the pressure is exactly 52 psi and not 55 psi. And the car rarely suffers from real oil pressure issues anyway. The stock guage is fine IMO.

That damn connection, or occasionally the sender are the sore spots for me. But I'd prefer dealing with them than another aftermarket gauge.

 

You make a good point. My oil pressure gauge is more a novelty another this point. Just something to fill the 3rd spot in the pod. I was making the comparison to oem water temp not in terms of function but in terms of reliability and accuracy.

But to the op, fix the stock one or go aftermarket. It really all depends how important monitoring oil pressure is to you and how much effort/money you want to put into this particular aspect.

In case you don't know, mazda deleted the oil pressure monitoring system entirely from the later model fds. From the factory, newer engine have a plug in the location of the oil pressure sender and the spot on the cluster was replaced with a boost gauge. Not sure if that will have any bearing on your decision but mazda saw it fit that it was unnecessary and opted for a boost gauge instead.

 

Another good point. Very few real oil pressure problems. Though the integrated low oil level alarm may have saved a few engines over the years. Did they keep that even though they got rid of the gauge?

 

Good question. from what I've seen, the oil level sensor still exists on the later engines so it has to be for something. I have a 99 cluster in my car, I will check if there is an oil light on it. If not an alarm, some sort of indication light at least.

 

Wow guys lots of good info thank you!

I guess I had assumed that a 91k mile rotary (this is my first) would be on its last legs. Good to know that the oil pressure likely isn't actually zero!

 

No problem....

I checked my cluster and it has an oil light. It's likely not for pressure since the ecu has no way of knowing that unless there's some complicated x+y=low oil pressure situation. I imagine it's for the oil level sensor.

 

^