Oil pressure dropping when stopping: Jeep Gr. Cher

[speechchick71]

I have a 2004 Jeep Grand Cherokee, V8, 4.7HO engine. mileage: ~167k miles. I had my oil changed almost exactly 3k miles ago and the same thing happened at the time mileage interval before previous oil change:

The oil gauge reports normal while driving and there does not seem to be a change in the performance of the drive. When I stop, the gauge drops to "low", the "check gauges" light comes on, and then it promptly returns back to normal. If I coast up to the red light/stop sign and do a very slow and gentle stop, it drops a little but not to "low" and also promptly (and I mean within 5 seconds) goes back to normal.

I'm finding it strange that it happened 3k miles after an oil change twice in a row. I don't think this has happened in the past and like I said, it doesn't seem to be running any differently.

Any ideas? Also, it is not leaking oil...at least there is never any oil under it where I park.

[tskeeter]

Three thoughts.

Low oil level. Your Jeep is getting high mileage. If it's burning oil, the amount of oil in the oil pan may be getting low by the time you get close to needing an oil change. Since the oil in the oil pan will slosh as you come to a stop, low oil level might cause the oil pump to suck air instead of oil for a second and cause the oil pressure to drop and warning lights to come on, then return to normal. Easing to a stop reduces the amount of the sloshing and shortens the amount of time that the oil pump sucks air. Check your oil level and top it off if it is low and see if the low oil pressure issue goes away.

Bad oil pressure sender. The oil pressure sender reads your oil pressure and sends the reading to your gauges, etc. Since you Jeep has quite a few miles on it, the oil pressure sender might be failing and need replacement.

Worn out oil pump. Again, you have quite a few miles on the Jeep. The oil pump might be worn out.



Based on your observation that this happens about every 3,000 miles, that it is worse if you stop aggressively, and you have a high mileage vehicle, I'm betting it's burning oil. The cheap fix, and the one I'd do if this were my car, is to watch the oil level and add a pint of oil when the level drops enough to take a pint. If burning oil is your problem, it will get worse over time. You'll probably find you need to check and top off the oil each time you fill with gas and start carrying a quart or two of oil in the car. But cars will run for quite a while even though they are burning oil. I'm betting that you could nurse the Jeep along to 200K miles or more just buy keeping the oil level where it belongs. If the car is burning oil, the alternative to keeping an eye on the oil is an engine rebuild, which I expect would cost over $5K.

[speechchick71]

tkseeter: awesome reply! Your first thought was my thought as well. I'll look into all the ideas but I suspect #1 is the thing. I've also read from different forums that the sensor might be bad as that is a common issue in Jeeps and Chryslers.

Thanks for your input!

[tskeeter]

If the oil is low and bringing the oil level up to full corrects the problem oil pressure reading and warning light issues, I don't think that I'd spend time and money looking further. You'd probably be looking for a problem where no problem exists. At at the cost of mechanic time these days, looking for a problem that doesn't exist gets really expensive real fast. Your car is kind of at the mileage where you say, as long as it runs, just drive it. And not spend more on it than you need to just to keep it drivable.

Now, if you're chick who is handy with a wrench and you want to do more diagnostic work, please have at it. I just have this thing about paying way more for an hour of a mechanic's time than I make an hour, when many people who call themselves mechanics seem to know less about wrenching than I do.