Jim Grant's Tech Tips

’00 Jeep Grand Cherokee, Oil Pressure up and down

Q: I was driving down the interstate in my ’00 6 cylinder Jeep Grand Cherokee and I stopped at a station. When I started the engine there was no oil pressure. After checking the oil & everything else it came back. Now about once a week the “check gauges” light comes on “no oil pressure” after it runs a little while it comes back. I changed the oil pump and the sending unit, oil and filter but it has not helped. The idle pressure is not as good as it once was but it’s okay. Seems to be a ghost. Is there such a thing as an oil switch on this model? I only know about sending units..

ED

A: The first thing you should know is that the oil pressure gauge along with just about every part of your instrument display is computer generated. That’s right it is not real. It is only the result of a computers interpretation of data that is then displayed on the instrument panel. The only hard wired (stuff that is connected to what is it’s displaying) is the 4 wheel drive indicator, left and right turn signal indicators and the brake warning light. Maybe they didn’t trust the computer with that type of information, who really knows? An oil pump is a mechanical device and when worn, loose or with a restricted pick-up screen can be erratic. If the engine has worn bearings then oil pressure will be low all of the time and not just once a week. You’ve done all of the right things with replacing the oil pump, etc. I hope the oil pan was cleaned and the pick-up tube & screen were replaced with the new oil pump. But now there’s a question of was the oil pump really the problem? Well the oil pressure gauge said there was a problem. But was it? Replacing an engine in today’s vehicles is big money and having that engine fail some place other than in a garage driveway causes more money and aggravation. Here’s what I would do. I would install a mechanical type oil pressure gauge. The type that has a line that takes oil right from the engine to the gauge for the pressure reading. You could do it 2 ways, just monkey it in as a temporary device or install it neatly for the long haul. Then just drive the vehicle and compare the dash display oil pressure to the gauge pressure. If there is a disagreement I would trust the mechanical gauge over the computer’s interpretation. If the oil pressure really does drop on both gauges, then you’d better be looking more closely at the engine’s lubrication system. If it goes the other way? Don’t you just love computers!