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Doug4230 08-17-2012 04:11 PM

99 Grand Cherokee oil pressure
Just lost oil pressure with no warning. Pressure went to zero, check guages light came on. Engine was one quart low, added oil and cured issue for the drive home, however pressure drops low 10-20 psi at idle now. No engine knock or other low oil symptoms.
I have had a similar problem during WINTER driving for quite a while now, but it always goes away after the engine warms up (during freezing temps) or in the summer months.
I am REALLY hoping it is not the oil pump as that looks to be a major job to replace.
Any thoughts?

4.7ho 08-17-2012 04:20 PM

Re: 99 Grand Cherokee oil pressure
Could be oil pump but a very common issue on WJ's is the oil pressure sending unit which gives inaccurate readings and sets off the dash lights. Does the oil pressure gauge increase after you add oil?

Doug4230 08-17-2012 04:37 PM

Re: 99 Grand Cherokee oil pressure
Was one quart low, pressure returned at driving rpm after adding to full but is still reading low at idle.

Frango100 08-17-2012 08:05 PM

Re: 99 Grand Cherokee oil pressure
As 4.7HO said, first change the oil pressure sending unit and see what it does.
Quite common that they fail after many years of usage.

4.7ho 08-17-2012 08:48 PM

Re: 99 Grand Cherokee oil pressure
If you do go this route you will need part number 5149064AA from the dealer. It runs around $50.00 IIRC and takes a deep well socket.

Doug4230 08-18-2012 08:00 AM

Re: 99 Grand Cherokee oil pressure
Yeah, that is my first plan. It was changed out once already in the past two years however. I have read that some aftermarket units do not perform as well as the OEM units, anyone have a comment on that?
If the sender does not help, I thought I would drop the pan and try to clean or replace the pick-up tube and screen.
I have also read that the return ports from the top end can get plugged and restrict flow. Any thoughts on that?
From the looks of the job, changing the pump does not seem worth it on a vehicle of this age.

4.7ho 08-18-2012 08:20 AM

Re: 99 Grand Cherokee oil pressure
When it comes to sensors the consensus here is usually to go with OEM as you stated aftermarket don't usually perform as well in the long run. Before dropping the pan to clean out the pick up tube/screen I'd recommend adding seafoam to the crankcase 50-100 miles before oil change to clean things up as it circulates through the engine. Just keep an eye on the oil to make sure it's not getting too dirty. As for "changing the pump does not seem worth it on a vehicle of this age." that comes down to personal preference. I will say my WJ gave me some headaches when things broke but it was mine and I liked it so I fixed them every time.

Doug4230 08-18-2012 09:04 AM

Re: 99 Grand Cherokee oil pressure
Used Sea Foam on last oil change, planned to do that again as well.
Vehicle has 200k plus miles and seems to develop problems faster than I can fix them. Cannot afford to pay a shop for the kind of job replacing the pump would be and do not have the time to do it myself. Jeep has been good, but....

4.7ho 08-18-2012 09:16 AM

Re: 99 Grand Cherokee oil pressure

Originally Posted by Doug4230 (Post 672074)
Jeep has been good, but....

Totally understandable and everyone comes to that point where enough is enough. In my case it was when the trans started to go which sent mine packing to find a new owner. Good luck & let us know which route you end up taking.

Frango100 08-18-2012 09:48 AM

Re: 99 Grand Cherokee oil pressure
When the oil pressure really is low, you will start hearing more mechanical noises, especially the valve lash adjusters. You will probably be good with the oil sending unit.
For removing the oil pan, you have to lower the exhaust Y pipe first, otherwise you can't remove it. I have my transmission out at the moment and the exhaust is lowered, so as soon as i have the transmission in again and before putting the exhaust back in place, i will also remove the oil pan and check/clean the oil pickup screen.

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