Jeep cherokee oil pressure drops to zero at idle

Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

My Oil pressure gauge started acting funny first going all the way to the top then started functioning in reverse Etc. Changed sending unit and then it rarely went over 40 even at highway speeds and drops to zero at idle. Checked it out at numerous shops and eventually changed the Oil pump where it now registers normal at speeds but still drops to zero at idle. Engine is smooth and runs great at speeds-no knocking or rough idle when gauge drops to zero. Has anyone ever experienced this issue? Last mechanic was baffled and says I might have a Crank shaft issue and That I should look for a used engine. Need Help/advice.

Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

cam bearing issue is more likely.

Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

Mine had the same issue -- the oil pressure would drop to zero only at idle (sounded fine when this happened). Turned out to be a cracked head. Basically, the coolant is leaking into the oil causing it to thin out. You might want to check the head as well. Since it is a 2000, just like mine, it has the 0331 head.

Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

First thing to do is to verify the readings on the dashboard gauge. Install a mechanical oil pressure gauge and see if it agrees with the gauge.

An engine with low oil pressure may run for many additional miles, so any discussion about engine swaps is premature until you verify the pressure and/or until it actually fails.

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Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

Quote:

Originally Posted by Tim_MN

First thing to do is to verify the readings on the dashboard gauge. Install a mechanical oil pressure gauge and see if it agrees with the gauge.

An engine with low oil pressure may run for many additional miles, so any discussion about engine swaps is premature until you verify the pressure and/or until it actually fails.

Yup, ran mine for over a year with this issue. Just had to change the oil more often.

Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

Thanks for the replies! To be truthful although the mechanic mentioned engine swap he did say that I should have no major concerns about driving the vehicle as it is for years to come!?? He said engine runs strong and smooth which is does. Never had any power or rough running issues so will see. Will check the Cam or head to rule those out and make sure he had a mechanical gauge attached.

Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

Quote:

Originally Posted by Tim00XJ

Mine had the same issue -- the oil pressure would drop to zero only at idle (sounded fine when this happened). Turned out to be a cracked head. Basically, the coolant is leaking into the oil causing it to thin out. You might want to check the head as well. Since it is a 2000, just like mine, it has the 0331 head.

This is sure a possibility with the 00-01. Are you having to add any coolant? One of the major symptoms of a cracked 0331 cylinder head is "unexplained coolant loss".

Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

Quote:

Originally Posted by birchlakeXJ

This is sure a possibility with the 00-01. Are you having to add any coolant? One of the major symptoms of a cracked 0331 cylinder head is "unexplained coolant loss".

As a matter of Fact I do have to add Coolant every week or so! Changing the Cylinder head would be a lot better than complete engine swap.
How can I tell for sure - What test can be done--Compression Test? HELP--LOL

Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

Only bad 4.0 block I have ever heard of had a huge visible hole in from a rod that got launched. The head is always the issue with an 0331 from all that I have read.

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Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

Quote:

Originally Posted by Gforce

As a matter of Fact I do have to add Coolant every week or so! Changing the Cylinder head would be a lot better than complete engine swap.
How can I tell for sure - What test can be done--Compression Test? HELP--LOL

1. Remove oil filler cap--with a strong light check head between cylinder 3 and 4, look for latte or coolant.

2. Check dipstick (crankcase) for latte.

3. Do a compression test on the engine.

4. Do a cylinder leak down test on no. 3.

5. Test for hydrocarbons in the cooling system.

One or more of the above will confirm the condition of your head/headgasket.

Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

Quote:

Originally Posted by joe_peters

1. Remove oil filler cap--with a strong light check head between cylinder 3 and 4, look for latte or coolant.

2. Check dipstick (crankcase) for latte.

3. Do a compression test on the engine.

4. Do a cylinder leak down test on no. 3.

5. Test for hydrocarbons in the cooling system.

One or more of the above will confirm the condition of your head/headgasket.

Thanks so much, I will check this out ASAP. Would that explain why last month when I got a tune-up the mechanic mentioned that one plug looked burned or fouled. Mechanic who changed the Oil pump this past week said the oil looked fine with no trace of coolant

Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

Quote:

Originally Posted by Gforce

..... Would that explain why last month when I got a tune-up the mechanic mentioned that one plug looked burned or fouled. Mechanic who changed the Oil pump this past week said the oil looked fine with no trace of coolant

Yes, that specific cylinder with the fouled plug is where
the crack is. Good news is that the oil looks OK.
A new head should fix it.

Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

Y'know, I'm all for saving money with intelligent repair choices but if the coolant is getting into the oil enough to thin it out, I'd at least drop the oil pan & check out the bearing conditions before I put a head on it. You might fix the leak, but it might be too late for the bottom end. Helluva thing to put a head on it & THEN find out your bottom end is shot...

Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

Quote:

Originally Posted by yossarian19

Y'know, I'm all for saving money with intelligent repair choices but if the coolant is getting into the oil enough to thin it out, I'd at least drop the oil pan & check out the bearing conditions before I put a head on it. You might fix the leak, but it might be too late for the bottom end. Helluva thing to put a head on it & THEN find out your bottom end is shot...

Antifreeze WILL destroy the bearings. It would be nice if it only took out the mains and rods, but it also eats the cam bearings. You need to pull the block to change those.
How long did you drive it with this problem. I drove my 2000 XJ with the cracked 0331 head 800 miles, returning from South Carolina. That was long enough to ruin all the bearings. It also put enough wear on the cam that I had to make a call. I chose not to replace it, but now I wish I had.

Last edited by MoFo; June 16th, 2013 at 13:07.

Re: Low Oil Pressure at Idle-2000 Jeep Cherokee 4.0L

Ouch.
In most cases it will be more cost effective to put a long block with a warranty in the car than to rebuild what you've got. Stroker or 4.0 is a tough call at that point.
Unless you can assemble it in the garage and are qualified to do so, driving something else while you get the machine work done & spend 40 hours or so checking clearances...