Hello everyone, I am a new member to the forum and just recently bought my first jeep. I bought a used 2000 Cherokee with 156k on the clock. When I bought the vehicle the oil pressure gauge would immediately raise to 80psi and remain there while at idle and through out the rpm range while driving.

First thing I did was replace the oil sending unit with a genuine sensor from the local jeep dealer.

After replacing the sending unit I would get 40 psi with cold start but when the engine warms up the psi drops off to 0 and the "check gauge" indicator lights up. Even while driving between 2,000-3,000rpm I only get 20-30 psi.

I did an oil change and replaced the Fram filter with mobile one filter and oil.

I removed the sending unit and and connected a Bosch oil pressure gauge into the port. (I did not have a test gauge. this mechanical gauge is one that mounts in the vehicle.) The mechanical gauge reads fine. Just below 20psi at idle and 35-40 at 2,000 rpm.

I would like to try another mechanical gauge to be sure. I have not had the jeep long enough to notice any drop in coolant that would indicate a head gasket or cracked head. is it possible that the oil pressure gauge inside the cluster is bad?

Any help would be great, I do not know if i have anything to worry about. The engine runs great, maintains a good temp, no unusual knocking or valve chatter, and no lose in performance.

Thanks,
Ross

 

You're on the right track. If the second mechanical gauge shows pressure like the first, I would assume the fault would be in the cluster gauge itself.

 

My question is... if the fault is in the cluster why would it register 40 psi at cold start? That seems accurate. ..

 

You did the right first thing for sure of getting rid of the fram filter. What oil you using in there. If youre reading accurate with the mech gauge consistently then something else is wrong like wiring. You can use a wix or napa good filter. Those are built well. And dont mix up oil pressure with flow. The range on jeeps are pretty wide sweep when it comes to oil pressure.

 

I put a mobile 1 filter. The store I went to did not have wix. That was there "best" filter. I am running pezoil high milage because I had it at the house.

The thing that really worries me is this cracked cylinder head that many people experience.

 

if you aren't losing coolant or having over heating issues or have milky oil, forget the 0331. Those heads can last with proper maintenance. As for oil, you can run some rotella or some mobil 1 and you can also substitute a bottle of MMO and run that for a 100 miles.

 

I just bought a real test gauge from napa. I am going to put the gauge on this afternoon and I will update the thread with the reading. Thanks for the help.

 

Well I just verified with a test gauge and it is like I feared, has 0 psi oil pressure at idle.

 

Anyone have any suggestions from here?

 

I'm not an expert but sounds like either the oil pump is not creating flow or your bearing clearances are bad. From what I have been reading bearing clearances is what determines oil pressure.

 

I looked in the oil fill hole and can see a trace amount of coolant. I think the cylinder head is cracked.

Does anyone no where I can get a complete head with valves and for how much...

 

Several things wrong here:

0331 head cracks regardless of maintenance, or not. It is a built-in casting flaw.

Marvel Mystery Oil is not approved for engine internals and dilutes engine oil, preventing the approved oil from doing its job. Voodoo additives are not needed or desirable.

 

Pull the engine and tear it down. Rebuild all of the old short block, and replace the head with a reliable new aftermarket one.

Your problem goes much deeper than just a head now.

 

That's a little low for a healthy engine. What we're trying to do here is isolate beyond a reasonable doubt if the gauge is accurate or off, by repeating the pressure test with two different mechanical gauges.

 

^This, if you have coolant in the oil and low oil pressure, it is likely that the head has been cracked for a while and the bearings have been damaged from coolant contamination of the oil, the engine needs either a full rebuild or replacement. Definitely don't put another 0331 head (or engine with a 0331 head) on it, use a new aftermarket head (Clearwater, etc.), a "TUPY" head (from 02-04 WJ or 02-06 TJ), or you can use a 0630 head from a 97-99 if you either fab something up to hold the coil rail or replace it with a Dodge Viper coil pack which can be remote mounted.