89 Caravan Low-ish Oil Pressure

Remember, these gauges are not at all precise. The first thing to do is to put a mechanical oil pressure gauge on the engine with it hot and idling to see what your *actual* pressure is. COmpare it to the spec or post it here. If the pressure is within allowable range, your dash gauge (or more likely, the sender) needs attention. If it is low, then it's time for some diagnosis.

You answer your own question here: The area below the normal zone is BELOW NORMAL. If your dash gauge isn't telling lies, operating the engine with subnormal oil pressure is a Bad Thing.

Guessing won't get you very far, but a clogged pickup screen usually shows itself at higher RPMs and/or when the engine oil is cold and thick, not at lower RPMs and/or when the engine oil is hot and thin.

Good point. I had assumed that since the pressure is towards the top of the normal zone when the motor is cold, and the pressure is much higher regardless of temperature when the motor is not idling, that the gauge was working correctly. But still, it could be a bad gauge or sending unit. I'll look into that.

I've seen old high mileage GM V8 motors whose pressure dropped to near zero at idle when hot, with no apparent ill effects. I had hoped the same might be true here.

That figures. Replacing the pump looks a lot harder than cleaning the screen.

Most common cause of low oil pressure at hot idle is increased engine clearances, due to wear. Using straight 30 oil will NOT improve this hot idle pressure over a

If the oil pressure comes up significantly at higher RPMs it is not likely the oil screen.

Also, is your hot idle set to spec, or has it dropped due to plugged idle speed control etc????

The straight 30 weight was simply what I happed to have four quarts of lying around, so I used it. My previous vehicle leaked enough that I kept extra quarts on hand, of whatever happened to be on sale.

Doh.

Good point, I'll check it today on the way to work. The tachometer is intermittent, but it usually works. Hopefully it is accurate.

By the seat of the pants, from memory, it feels kind of low. The motor is so quiet at idle that you cannot hear it inside the vehicle. In Drive, idling without my foot on the brake, it creeps forward much slower than most other vehicles I have driven. But it never dies, so I assumed it was ok.

I agree with everything Dan said about checking the actual pressure at the oil sender using a mechanical gauge, but just wanted to offer that my 1991 Mitsubishi 3000GT SL (same engine: 3.0L V6 dual cam, no turbo) behaves pretty much exactly as you describe. It currently has 127K miles and has behaved in this manner for the 2+ years I have owned it. At start up the oil pressure gauge immediately jumps to the middle range at idle, but as the engine warms up (3-5 minutes later during summer), the pressure drops slowly to the low end of the gauge. If I step on the accelerator and increase the RPM slightly (to above 1K) the pressure rises back to mid range and stays firmly at upper mid range when driving at highway RPM. If I drive in stop and go, then the pressure drops at every light/stop.

My gauge appears to be accurately displaying/communicating the pressure and at higher RPMs seems fine, so I've come to the conclusion that the oil pump needs to be replaced. I don't plan to do this anytime soon since the entire engine needs to be overhauled and this will need to be done at some time down the road when I can take it out of service and afford the work and coupled with the interval for replacing the water pump and timing belt again. The reason I want to overhaul the engine is because it burns about a quart of oil every 1500 miles and the valves/heads are very noisy, especially at start up and until the engine warms up. I've recently begun using Mobil 1 10W-30 and this appears to have helped since the valves quiet down in about 1-3 seconds after start up, as opposed to the 30-60 seconds when I used regular non-synthetic oil.

Based on what I've read on this and the Mitsubishi newsgroup, my experience with the 3.0L (and yours too) seems to be pretty much the norm.

Bob

Again: Guessing won't get you very far. You are guessing (without any basis) that changing the oil pump will fix the problem. It may or it may not. If your insufficient hot-idle oil pressure is due to excessive internal engine clearances, replacing the pump won't fix it.

Hi

This may or may not be a problem Most motors have lifters that require oil pressure to work. This means if the oil pressure really is low, the motor will click loud enough that you won't be able to hear yourself think.

Larry

Now that you mention it, it never makes any racket even when the pressure reads low.

Assuming the tach is accurate, when hot it idles at 625 to 650 RPM.

There seems to be no way to set the idle; both the Haynes manual and the sticker under the hood says the idle is preset and can't be adjusted. Neither bothers to say what the idle is supposed to be.

That describes my motor exactly.

That's the best news I've had all day.

Sometimes, a guess is all I've got.

Unless it gets worse, I won't do anything major.