My wife’s '01 Jeep Cherokee is reading low oil pressure at idle (5 to 10 lbs). The 4.0 liter I-6 engine only has 96,000 miles on it. The mechanic said it could be the oil pump, but it is likely the engine bearings. Rather than test a new oil pump and lighten my wallet by $400, we tried changing to thicker oil. The thought was that if the pressure went up that the oil pump was working and it was the bearings. The pressure went up. The mechanic says we should drive it until the engine dies and then replace the engine. He also recommends frequent oil changes (every 2,000 miles) with the thicker oil. Questions: 1. was our test and diagnosis good? 2. is this the best solution? is there any oil goop like STP to help? 3. it doesn’t seem right that this should happen this early. This engine was supposed to be a real work horse. I didn’t find any tech doc on this problem, but I’m not sure I’m looking in the right place. I’m open for other thoughts.
Have you had the oil pressure checked mechanically? It could be a bad pressure gauge sender. Also, what is the idle speed at? If it’s idling at 500 or so, 5-10 lbs isn’t too bad and kicking up the idle a few hundred RPM’s might kick the pressure back up without any ill-effects. First check that you’re idling at the correct speed.
I will say that on this forum we seem to get a lot of people with these engines with this exact problem. It sounds like this might just be a normal part of aging for these old straight-sixes and it might be that the only people who are complaining about it are astute individuals like yourself who actually look at their oil pressure gauges.
You could mask the problem with a thicker oil or upping the idle speed a little but low oil pressure at idle isn’t actually harming your engine, it’s just the symptom of possible engine problems. Unless it really bothers you, I wouldn’t do anything other than keeping an eye on it and checking the oil level regularly.
Before shelling out big bucks you should consider either testing the oil pressure with an external gauge or simply replace the oil pressure sending unit (this controls the dashboard gauge reading).
I’m a bit suspicious of your mechanic for not suggesting the simple, cheap obvious first. He’s starting at the back of the book and working his way forward.
My feeling is that a reasonably maintained vehicle with only 96k miles should not be suffering from an engine bearing problem or an oil pump problem. (The latter is often misdiagnosed)
The thicker oil also has an affect on oil pressure sending unit resistance with the changing resistance being what controls the dash gauge anyway.
He actually did put the external guage on. I forgot to mention that. So allowing for that, are you saying that the experiment wouldn’t eliminate a possibility? I found out today when I stopped to pay (I picked the Jeep up just before the holiday) that he acutally added an additive (Lucas?) with regular 10w40 oil. Thanks for the advice!
Hadn’t thought about the idle. I’ll check that. If it isn’t bad at just low idle, that would be good. My wife won’t give this thing up (hence my handle), but I get nervous if she goes on too long of a trip.