Okay went for a drive in the mountains as I do most Sundays. Drive for about 30-45 minutes on the highway with no problems, mostly cruising in 5th. Get to the mountains and start driving through the canyon. I got stuck behind some slow cars and was driving at like 4-5k rpm in 2nd with a low amount of throttle. I notice the oil pressure start to rise to 70 psi and then blow right through that to max. I turned the car off and pulled off for a few minutes, this is a very narrow road and I didn't want to be a sitting duck so I turned car on and drove some more. Pressure was normal for like a minute and then rose again. Pulled off first chance into a ditch and promptly ran over some barbed wire. Waited ten minutes turned around and and drove under 3k rpm back. I didn't notice any problems. Cars temp stayed normal the whole time, didn't notice any smoking or anything out of the ordinary.

Time to look for 12a parts?

 

A more optimistic perspective would be a bad oil gauge or sensor.

 

What failure could you think of that would result in extremely high oil pressure?

Don't say oil cooler line failed internally, the oil pressure sender is after the lines.

The answer is none... and the Mazda senders AND gauges are known to be flaky.

 

I would suspect the pressure sender. On my '82 (a gazillion years ago) the oil pressure went to max on a normal drive. Pulled the sender off and connected it to a bicycle pump to test it out. Kept it connected to the car gauge, and had to connect a ground to the sensor. Pumped it up and it worked ok. Put a little oil in my test line so the sender had oil against the sensor and pumped it up again. This time the reading went to max. New oil pressure sender fixed it. A few years ago my '85 had goofy readings. Again replacing the sender fixed it.

 

Thanks guys, I'll check that and post back. After cooling the car off for 30 minutes and driving home it was fine, but it scared me nonetheless. I've had a car blow a head gasket, and I was panicking, thinking not again.

 

The good news is that 12A's don't have a head gasket.

They just don't like to be over heated, so watch those engine temps carefully.

Probably just the sender.

 

Yea I'm just paranoid though, I constantly check my temps and oil pressure, definitely don't want to overheat the engine, especially such a low mileage engine. Going to replace the sender and then we'll see. I just saw the pressure gage climbing and panicked from memories of my Outbacks temp gauge rising. But head gaskets are like a normal maintenance item on Suburus

 

I would feel the same uneasiness if the oil pressure gauge was getting wacky, you need to know what is causing this.

A friend of mine with an 85 GSL has a similar problem, although I can't remember the exact symptoms. In his case it turns out to be related to the capacitor that sits on top of the engine being bad. These capacitors are very hard to find so although he knows the oil gauge is inaccurate, he still doesn't have that critical information, not a good situation.

 

I purchased a new oil pressure sensor (and also a temperature sensor for good measure), so I'm going to replace those once I get them and we'll see.

 

Sometimes just cleaning up the contacts on the senders does the trick, but these parts are sufficiently inexpensive and important to just go ahead and replace them, needed or not.

 

That's my thought, I'd rather error on the side of caution.

 

My temp sender went bad. In the FSM there is an ohm reading for cold. Mine was sky high compared. So the temp gauge never went to normal operating temp. Unfortunately every time I drove it I was running hot and eventually blew the engine.

Yes, when I replaced the temp sender I replaced the oil pressure at the same time. On my 12a to get the temp sender out, its easier to remove the oil pressure first.

Its also possible to test the temp gauge with a 47 ohm and 22 ohm resistors. Just connect the resistor to the sender wire, ground the other end, and turn the key.

 

Thanks for sharing. I ordered both, and hopefully I can replace them and be up and running this weekend again. While I do want to rebuild a rotary engine at some point, I don't want to rebuild this one

 

I replaced the sending unit today, but now my oil pressure is reading very low. This is right after the choke has popped in:


idle


3000 rpm

Why is it so low? There are no oil leaks anywhere, and the engine has plenty of oil in it. The only thing I could think is that I didn't screw the sending unit in far enough. I still have some thread visible, but I was getting quite a bit of resistance, so I figured I had it in far enough.

Thoughts? I'd really like to drive my car again, but I'm afraid to since the oil pressure is so low.

 

Be careful not to over-tighten the sender. It doesn't need to be too tight. Make sure you have e a good connection with the sender. A lot of time the wires in that area con become brittle from heat.

Might want to consider adding a aftermarket gauge. You would need to get a oil pedestal sandwich or new aftermarket oil pedestal. This will depend if you have a front mount oil cooler.

 

my friends Rx7 did something like the original symptom. (intermittent high oil pressure), and it turned out to be that the condenser has a wire with some broken insulation, so it sometimes ground, which gives max oil pressure. fix was just to fix the wire.

condensor is/was bolted to the clutch slave/flywheel inspection cover, little black box thing, 1 wire

 

I got the sender as tight as I felt I could get it without stripping it or overtightening.

Yea, the wires are all exposed and nasty looking, and looks like oil has been spilled on them constantly for 30 years.

I'll check the wire connection and see if anything looks obvious. I don't know anything about wiring, what's involved with replacing the wire, I assume just cutting it and soldering on a new connection? What else could be the problem, is it possible the oil pump is failing or is this pretty typical of the gauges being flaky. I want this thing to be perfect, I expect the gauges to give me a general idea of what's going on with the engine.

 

Change your oil.

Use 15-50 mobil, as it doesn't thin from gasoline. Your factory carbed setup runs at 12.0:1@7k at WOT. If you drive it hard, gas starts to thin the oil. Causes short oil life, and obviously low psi.

 

An oil change is not a bad idea, if it raises the pressure to the "normal" range that would be the cause.

But looking at your gauges I'm not so sure there's anything wrong with your oil pressure.

At idle your reading looks like about 10 lb/in2; the FSM calls for 13-38 lb/in2 at idle.

At 3000 rpm it looks like you are getting about 50 lb/in2; the FSM calls for 64-78 lb/in2.

The stock gauge is not a precision instrument, especially a 30 year old stock gauge.

You are right to be concerned about oil pressure readings but you might be worrying too much.

But if you really need to know I would suggest an independent method for measuring your oil pressure, not the stock gauge.

 

Hmpf! Oil pressure gauges, another reason to own an SA.

No such thing on my car, just an idiot light somewhere at the bottom of the console.

I agree with Ray, oil change may "fix" but there may be nothing to fix, it could be the extra
resistance in all the wiring as it goes to the guage or the guage is not as sensitive as it used
to be.

You worry a lot, relax and have a homebrew!

 

I guess the main reason for my concern is that it was reading in the normal range with the old unit (disregarding the extreme spike while driving), but now it's reading low. I'm going to fiddle around with it after work.

For the regard I'm always worrying that I've broke something on my car, even if everything is working correctly. I'm just a worrier .

 

Okay, so took the connector off of the sender and wiped it off the best I could, put it back on and took the car for a drive. At idle the gauge read ~15 psi, at 3000 rpm (well anywhere, took the car to redline) it read ~40-50 psi. The lower limit for 3000 rpm is 64 psi, so that's a good deal off. What confuses me is why it read higher with one unit and lower with the new unit. Is it possible the new unit is borked, it's brand new? Didn't have time to do an oil change this evening, will do one later in the week. I guess I'll drive the car to work tomorrow, unless anyone can think of a good reason not to. Maybe it's just flaky 30+ year old hardware. This highly bothers me though.

 

Did you use thread tape when mounting this? Maybe its affecting the conductivity in some way.

 

Nope, considered using anti-seize, but decided not to. Usual disclaimer: I have no idea what I'm doing. Interestingly enough this is the second car I'm currently restoring

 

I'd be curious what the reading is using Tim's resister check?

Tim Wilbers...
"Its also possible to test the temp gauge with a 47 ohm and 22 ohm resistors. Just connect the resistor to the sender wire, ground the other end, and turn the key. "