I had the oil changed in my 1985 IROC today. While that in itself isn't necessarily newsworthy, my oil pressure seems to be. I normally run Valvoline 10W30 Maxlife in my 305 TPI with 150K miles on it. Today, I switched to Castrol 10W30. (They were out of the Valvoline). I figured if Castrol was good enough for my wife's Lexus, then it should be good enough for my Z. While driving around today, I noticed that while stopped at a stop light, my oil pressure gauge was on 0. I shifted into neutral and it moved up, but not out of the red. When I pulled away, it went up a little and them began acting erratic. It normally reads about 30 psi when driving and would usually settle down close to the red at idle. I did not experience any symptoms you would expect from an engine with no oil pressure. Do you think it's the sending unit, and if so where is it located?

 

First thing is to make sure you have good oil pressure with a direct reading guage. The oil sender is on the side of the block just above the oil filter. The odds are in favor of the sender part of the switch being the problem. if oil pressure actually drops to 0 the fuel pump should get shut off by a second ckt in the oil sender

 

The most likely thing that happened, by far, is that the OPSU just happened to fail at about the same time. What you're describing is VERY typical of how they go bad.

While hooking up a mech gauge is a great way to troubleshoot it, I'd suggest just changing out the OPSU. It costs less than a gauge, and takes less time and fooling around than adding another gauge; and more than likely, all you'd find out with a gauge anyway, is that you need to change out the OPSU. In other words, fooling around with a mechanical gaige saves you neither time nor money. I'd recommend bypassing all that and just go directly to changing out the OPSU.

In your year, I believe the OPSU is next to the distributor, behind the intake manifold.

 

Agreed with Sofa. VERY typical of how they act when they fail.

The oil pressure sending unit for the gague is screwed into the block just above the oil filter boss.

 

That's got to be what it is. I drove it to work today and everything seemed to be just fine. It was 17 degrees here this morning and right after I started it up, the gauge read between 30 and 35 PSI. After it warmed up, it dropped and at idle, stayed just above the red. The OPSU has never been changed. Is it a bear to get out? It's now going on 22 years old and 150K miles