Glad to hear you've found the culprit. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Oil pressure gauges often read low on our engines - even if pressure is really ok. You can try changing the sender to see if you get a better reading - or - you can try replacing the gauge... which is a bi-metal lever controlled by an internal voltage limiter and can be damaged by any voltage spikes from the alternator. If you really want to see accurate oil pressure information, replace the gauge with a mechanical one.

Frank

Well thats good to hear.. and makes sense.. Cuz it was fine before all this..

Want to take a second and say thanks to everyone that walked me through this.. and I hope this feed helps any others with the same problems.. Alot of Great Info.. !!

No, not surprised. That's why it's listed as Stupid Little Box in the parts catalogs...




Is this per a factory gauge or aftermarket? And, how low are you talking. 10-15lbs at warm-hot idle is not unheard of on a factory gauge.

Yeah its factory and around that.. but seems to run fine.. no nock or anything.. So i'm guessing its the stupid lil gauge..

That's what it usually is. Do what Frank says and put a mechanical one in. More reliable and faster reacting <img src="/forums/images/graemlins/kewl.gif" alt="" />

The stars shake in their courses. The earth trembles. The shape of space is warped. I think there's a small possibility Frank may have made a mistake. Only a chance, you see, since I've never actually taken an OP gauge apart, or the sender, and I don't have any manual for the wiring diagram but the one for an 89, but I think the OP gauge and sender work off 12v 'lectrons. Only the fuel and water temp gauges work off the voltage limiter. I don't dispute the possibility of warping the bimetals anyway, tho...

My experience with the stock gauge is that in addition to being purposely overdamped to the point of limited utility, it has a sender that deteriorates, either with a leaky diaphragm, or with a deep fried internal rheostat thingy, and either reads low (part of the pressure leaks out thru the sender onto the motor and ground) or not at all, or with dead spots in the range. There is no real substitute for a good mech oil gauge. Plus a low pressure alarm of some kind.

Anything is possible - and certainly I reserve the right to be wrong - but, on Page 8-163, the '89 FSM describes the oil pressure gauge and the oil pressure gauge unit as "Bimetal type". I'm not sure if the oil gauge circuit is voltage-limited - but I'm assuming any and all of the bimetal gauge units are, since over-voltage would wreck them. I haven't checked the schematic, though. I have taken apart a gauge cluster and found the voltage limiting circuit, but don't remember if it protected all of the gauges or only the fuel and temperature gauges.

The fuel gauge bimetal and maybe the ECT gauge bimetal certainly can be damaged by alternator voltage spikes, so I would think the oil pressure gauge might also be susceptible..... but I'm not certain of that.

In any event, the oil pressure gauge unit can be checked with an ohmmeter across the terminals - the standard value is 50 ohms.

Frank

I've got a dash pod apart working on putting AutoMeter gauges in it. I was surprised to see how flimsy and cheap feeling the OE gauges were. I don't have the pics handy, maybe I can find them this weekend and post them.

I think Eddy is correct that the oil pressure gauge is not voltage limited. It looks like only the fuel gauge and temperature gauge have their signal voltage reduced to 7v. Thanks for the correction, Eddy. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Frank

Gotcha...

Score now stands 1 - 23,456...

Note that resistance testing of the sender will not assure no leaky. Get a mech gauge. I have little faith in 'lectrons...