I recently resurrected my '87 Trooper (2.3) from a long sleep - thanks in part to the folks on this forum.

However, now that it is running, I have what I THINK is just a wiring or sensor issue. When I start the engine, the oil gauge (factory) indicates slightly over 55 psi and the oil light is not on. After about 10 minutes or so of running, the gauge will gradually drop down to the low end of the "acceptable range" indicated on the dial - around 30 psi at 3000 rpm, but the oil light will come on. There doesn't seem to be any loss of performance when it comes on.

Does this sound okay? Is there a separate oil pressure switch to the oil light? (The two wiring diagrams I've looked at seem to indicate different things).

I've been driving it for short trips with the rationalization that if the gauge is okay then the engine is probably fine.

I don't know if it makes a difference but I'm running 10W30 oil in it now. It's only got a few hundred miles on it, but already it's black. Also, this vehicle had been sitting for several years. I had trouble getting it started, but it seems to run okay now (I did use a fair ammount of starter fluid, which I understand is bad).

Thanks for your help.

Might want to try a 40 weight to see if the psi stays up first. Did you put new oil in it when you got it back running? If you didn't the oil could of picked up the contaminants on the bottom of the pan causing the oil to turn black. It could also be causing your oil filter to be clogged causing your psi to be low.
If you want to find out if there's one or 2 sensors, trace the wiring or just look for the oil pressure sensors. If theres only one check to make sure the wires are hooked up good.

85troop,

I did put new oil in, but the engine was cold when I drained the old oil out. Like you mentioned, there was probably plenty of contaminants left in the bottom of the pan.

I haven't had time to trace down the wiring yet.

Thanks for your advice.

Martin

I don't know if the 87 has two sensors... I pretty sure my 88 does have two.

But, in another thread, a (good) suggestion was made to hook up a known good mechanical gauge to verify actual oil pressure. I personally wouldn't drive it until I was sure I had good pressure.

It should have two sensors, one right above the oil filter that runs the gauge and a smaller one further back on the block that runs the warning light. I wouldn't trust either of them completely, could be the light sensor is reading lower than it should (clogged or just bad) or the gauge sensor is reading higher than it should. It might be that there is a clogged passage somewhere between the two or something like that that explains the difference. Only way to be sure is to hook up another gauge, preferably mechanical and verify the actual pressure.