Low oil pressure on our 2000 XJ

Hey Everyone,
I am a little mystified by a problem my wife and I have with her 2000 Cherokee Sport. It is a 4.0L auto with 62,500 miles on it. Recently the oil pressure has been dropping to 10 psi after it has warmed up. I just changed the oil to see if it would help. It didn't seem to make a difference. I thought maybe the sending unit was bad so I mounted a gauge in the pressure fitting and the gauge also says 10 psi. It goes up when you step on the gas pedal, but 10 psi at idle seems low to me for such low mileage. The Jeep also seems to be using antifreeze, but has no leaks or any traces of leaks. I am starting to get concerned that I am going to have major engine work in my future.

Anyone else experience these types of problems on an XJ with less than 100,000 miles on the odo?

Thanks for any help you can provide.

Andy

What brand oil filter ?

warranty???

Got head gasket? Using coolant is a sure sign. Check your oil for the missing coolant.

normal idle oil pressure is 13-20 psi and anything above idle(1600rpm) should be 20-70PSI


^paraphrased from haynes manual

Andy in Pa. said:

Hey Everyone,
I am a little mystified by a problem my wife and I have with her 2000 Cherokee Sport. It is a 4.0L auto with 62,500 miles on it. Recently the oil pressure has been dropping to 10 psi after it has warmed up. I just changed the oil to see if it would help. It didn't seem to make a difference. I thought maybe the sending unit was bad so I mounted a gauge in the pressure fitting and the gauge also says 10 psi. It goes up when you step on the gas pedal, but 10 psi at idle seems low to me for such low mileage. The Jeep also seems to be using antifreeze, but has no leaks or any traces of leaks. I am starting to get concerned that I am going to have major engine work in my future.

Anyone else experience these types of problems on an XJ with less than 100,000 miles on the odo?

Thanks for any help you can provide.

Andy

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Has the engine overheated recently? The 0331 heads on the newer 4.0's have been known to crack on the top side between the no.3 and 4 exhaust ports and if that's what's happened in your case, it's bad news. You might not get any coolant contaminating the oil but merely be losing coolant through the exhaust. I suggest you get the cooling system pressure tested to see if you do have an internal leak. Take the radiator cap off and run the engine at idle. Bubbles constantly appearing in the radiator are probably from the exhaust and will be a sure sign of either a cracked head or a head gasket leak.
The oil pressure is a definite concern. Assuming that the oil level in the pan is correct, you have a new oil filter (not Fram I hope), and the 10psi oil pressure reading at idle is correct, you'll probably need to remove the oil pan and investigate. Possibilities include worn oil pump (unusual at only 62.5k miles), clogged oil pump pick up screen, or worn rod/main bearings.
These are not the sort of problems you'd expect to find on such a low mileage engine but if you only bought your Jeep fairly recently, can you rule out the possibility that it was abused by the previous owner?

RichP said:

What brand oil filter ?

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First thing I thought too - crappy filters like Frams are known to contribute to low oil pressure.

It is a Fram oil filter, but I just installed it. Its the Mustang 5.0L PH-8A. It has been overheated (due to low antifreeze!), but I had the coolant system pressure checked and it held just fine.

It is easily within that oil pressure range @1600 rpm, but thanks, I was hoping someone would provide that info too. I don't have a troubleshooting book for the 97-01 XJ's.

Definitely no coolant in the oil, that was my first thought too, and no, its not under warrranty.

We have owned this Jeep from new, my wife drives it 5 miles back and forth to work each day. Most days it barely has time to warm up before she is pulling into work.

Another thought, I didn't think about this last night, but it seems it is idling very low, like around 500-600 rpm. This would certainly contribute to low oil pressure, but what would cause this? I am thinking the idle stepper motor dirty, or maybe a partially blocked breather line.

Thanks for the ideas so far!!

Andy

Sorry man but the filter is the problem. My 98 picked up about 15 lbs at idle and 20+ on the road when I switched over the the Napa Gold filter from the generic filter that was on it when I bought it. I also noticed a big diff on my 94 Dakota 5.2 when I moved from the Fram TG to the Napa/Wix Filter. For the money, the Napa Silver (or used to be called silver) is superior to Fram and the Gold is IMO the best out there for a reasonable price. Dump the Fram...... been there, done that, got the T-shirt and it sucks.

Travis

Unfortunately, Dr Dyno is most likely correct. The low oil pressure comes from having the engine oil contaminated with coolant, which probably damaged the bearings. You won't be able to tell just by looking at the oil, there just isn't that much coolant in the oil, but it is there. Just take a flashlight, remove the oil fill cap, and look directly down at the head itself. The heads normally crack directly under the oil cap, right between the #3 and #4 exhaust valves. If you look and see some crusty green residue, your head is cracked. Another way to check is to add dye to the coolant, and then use a UV light and look down at the head.The leak is small, but it is just enought to do damage to the lower end. Coolant, oil and engine bearings don't mix well at all. If you are not sure how to check it, go to your local Jeep dealer and have them look, they will know exactly where to look and how to test it. Good luck, I hope I am wrong, but after seeing so many heads crack and changing complete engines at the dealer, you need to get it checked.

Bryan

I would like to know more details about these head cracks. It seems that a head replacement is a temporary fix. What is the source of the problem?

1)What years/models are more prone to cracking?
2)Is it caused by overheating?
3)How many miles?
4)Is it more frequent in winter or in summer?
5)Is it a design flaw or maybe a casting defect?

Thank you for any input.

The 5 miles a day is the killer. Your situation out of most here is a good enough reason to justify and be running synthetic. It's superior lubrication on cold starts like that will keep the bearings from wearing out early. The type of driving you are talking about is above and beyond 'etreme duty'... The filter is not helping either, try a purolator, K&N, Mobil-1 or Mopar, anything but fram and it's 'relabled' clones...

I think Dr. Dyno and Bryan C. are on the right track. You need to check the head. Check it as Bryan C said. The later model head cracks on the top of the head and leaks into the rocker area. The green/white crusty line will be a giveaway. Obviously, it could be other things. But this is not all that uncommon on that particular head.

Mar said:

I would like to know more details about these head cracks. It seems that a head replacement is a temporary fix. What is the source of the problem?

1)What years/models are more prone to cracking?
2)Is it caused by overheating?
3)How many miles?
4)Is it more frequent in winter or in summer?
5)Is it a design flaw or maybe a casting defect?

Thank you for any input.

Click to expand...

The 0331 casting heads on '99+ WJ and '00+ XJ/TJ 4.0's seem to be the most crack-prone. I don't know if DC changed the casting to reduce weight but they seem to be very sensitive to overheating and tend to crack topside in the middle between the no.3 and 4 exhaust ports (the hottest part of the head). As you can imagine, most of the heads that meet their demise are on youngish, lowish mileage engines. I saw three cracked 0331 heads sitting on the floor in the Jeep workshop that installed my stroker. The chief mechanic there told me these new head castings are junk.

My jeep matches the same conditions as "Andy in Pa." only after reading another thread here I changed my oil and put in a heavier weight oil (thinking that would solve the low oil pressure). Only now I find that oil has backflowed over my engine from where I poured it in and the engine kicks like it has low oil when gently accelerating (x1500rpm). In checking the oil I find it is not low...yet I am low on coolant. In reading this thread I will check the cylinder heads for cracks. I really don't know what I am looking for or how to assess the damage. A buddy of mine said it might just be the gaskets. Any help on what to look for other than what has already been posted?

...well, I think I'm screwed. Removing the oil filler cap I see traces of coolant-green and there is a brown glue-like compound stuck to the bottom of my cap (from when it over-flowed?). Heavier weaight oil was probably a bad idea. I couldnt get eyes on my cylinder heads or the 0331 for that matter, and I still don't know what to do aside from changing my oil again to prolong the inevitable. Any thoughts?

same diagnosis here. so whats the fix and since this is an obvious problem whats D/C doing for us? will the dealer have the new head in stock? or is this one of those things D/C is saying didn't happen and its a special order?
TIA

FIrst off don't panic, if you engine has oil all over it clean the engine first, second go the the recommended oil, either 5W30 or 10W30 and a good oil filter, you need to baseline it so go with a Mopar stock OEM filter. Change the oil and run it to see what happens. The engine 'kicking' can be from being in the incorrect gear, my 98 w/5 speed will do it on hills if I'm in 4th and try to accelerate when I should be in 3rd.
The brown stuff that is in the top of the filler cap is normally from moisture in the oil, result of short trips and not getting the oil hot enough to cook the moisture off.
For a quick coolant leak into the engine check do a plain old sniff test with the mark1 mod 0 nose on your face. Stick it down by the exhaust pipe and take a small sniff, not a deep breath. Your nose should be able to smell anti-freeze provided you've smelled it before. If you can smell it then you will need to check it further, if not then the system is probably OK.

ayers05 said:

...well, I think I'm screwed. Removing the oil filler cap I see traces of coolant-green and there is a brown glue-like compound stuck to the bottom of my cap (from when it over-flowed?). Heavier weaight oil was probably a bad idea. I couldnt get eyes on my cylinder heads or the 0331 for that matter, and I still don't know what to do aside from changing my oil again to prolong the inevitable. Any thoughts?

Click to expand...

Don't bother changing the oil again. You'll just be wasting money unnecessarily without solving the problem.
Check the plugs and see if any of them look cleaner than the others. Plugs that are being contaminated with coolant leaking from the water jacket will misfire and cause the "kicking" that you've described. I also suggest that you check the compression in all cylinders.
Since you definitely have coolant contaminating the oil, remove the valve cover and inspect the top side of the head. I hope I'm wrong about it being cracked because it would suck big time if I'm right. If there's nothing obvious and the compression is low in one or more cylinders, you'll need to remove the head. The head gasket could be leaking and the head itself may be cracked between the water jacket and an exhaust port. If you can't see any cracks with the naked eye, ask a machine shop to magnaflux it for you.
As for the low oil pressure problem, pull the oil pan and check the rod/main bearings. Your oil may have been contaminated for a long enough time to cause severe bearing wear. If you find both the rod and main bearings are worn, assume that the cam bearings will also be worn in which case, you're looking at a complete engine rebuild.

JVRacer04 said:

normal idle oil pressure is 13-20 psi and anything above idle(1600rpm) should be 20-70PSI


^paraphrased from haynes manual

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Haynes is wrong. (Or you paraphrased it wrong.)

FSM says 13 psi (minimum) at idle, 37 to 75 above 1600 RPM.

Over the weekend I installed a NAPA Gold (Wix) oil filter, and I cleaned the throttle body, concentrating on the air/idle stepper motor seat. The idle is marginally higher and the oil pressure is marginally better, but I have not driven it for more than 15 minutes yet. I have a long drive on Thursday that will be the true test. I plan on looking inside the valve cover at the head for any signs of a crack, I'll check that tonight. The engine runs very smoothly though. No bottom end noises or knocks.

We'll see....I'll keep you all posted.

Andy