captain_k

2000 XJ 4.0 straight6, 135k miles.

When the engine is idle the oil pressure reads 0 and the "check gauges" indicator is on. When I press the throttle and get going above 20 mph, the pressure rises to about 20 (on a 0 - 80 scale) and the indicator turns off. But as soon as I let off the throttle or come to a stop the needle falls back to 0.

I'm thinking oil pump? Could it be anything else? How bad is it to drive it with low oil pressure until I can fix the problem? The temp isn't getting too high.

Thanks as always!

BlakeDGKleavitt

Mine does this too!! Really annoying

5150mechanic

sending unit if you're lucky, prob. cam bearings,,,

99 Purple XJ

If your lucky it could be the sending unit but sounds like you might have a cracked head google 0331 head theyre known for cracking between 3 and 4 cylinder do you lose any coolant? I wouldnt drive with low oil pressure its bad for the engine

BlakeDGKleavitt

I loose coolant. What am I lookin for when I google 0331 head?

wjnfirearms

My esteemed bros....let's not put the fear of God into this guy. Just not yet.

This is a common complaint we have with these vehicles. My '98 did exactly this recently. Ended up being the sending unit and nothing more.

The "CHECK GAUGES" light relates to the dash gauges and what they show, nothing more. It is responding to the "0" reading of the oil gauge, not what the pressure may really be.

You don't relate any other symptoms like the valves getting noisy at idle or performance issues which make me suspect the sender. The best way to know for sure is to get your hands on an oil pressure gauge for diagnostics. They aren't expensive, unless you go for Snap On or one of the other professional brands. You remove the sender and attach the external gauge where the sender is screwed in just below the distributor. The reading will tell the tale for sure. If you just want to replace it for general principles, all parts stores carry them and they aren't the most expensive sensor these engines have.

I always believe in exploring the simplest solution first. It often is the least expensive and most common fix.

jebmccall

if you truly have low oil pressure and you continue to drive it the engine will grenade. verify youre oil pressure with a mechanical gauge. oil psi spec is minimum of 13 psi at hot idle, and i believe 35 + psi above 1600 rpms.

check the simple stuff first. check youre oil level, check coolant level for signs of oil. then check youre psi with mechanical gauge. if it is indeed low pressure take the pan off inspect you're rod bearings, change the oil pump. and let us know. btw does it make a knocking sound?

84zmyfavorite

Check the under side of the oil fill cap, and inside of valve cover(where you would fill with oil. Hopefully you wont see a milky, cream looking film. If you do, then you have a Bad internal coolant leak, possibly caused by the infamous 0331 cylinder head cracking between cylinders #3 and 4 exhaust ports. The crack coincedentally would be straight below the oil fill cap to the right, or drivers side. If the crack is big enough, you might be able to see crusted, greenish yellow coolant residue line that would indicate a crack beneath. The coolant mixes with motor oil, and corrodes engine bearings(Crank, Rod and Cam bearings) which increases clearances and results in low oil pressure. Hopefully this isnt the case, and you have a bad oil presssure sending unit. But if coolant is being consumed, I would look for that crack, or have a oil analysis performed(BlackStone Labs) and see if there is indeed coolant in the motor oil. If you know how to work on motors, and can do the work yourself,replacing the bearings is actually fairly cheap. Alabama Cylinder heads produce very High quality and Heavier duty(thicker casting) cylinder heads than factory for $539 to your door. Or 2002 and newer 4.0 cylinder head from a salvage yard will be improved and compatible for your Jeep. Good Luck to you. I hope the best.

Carl48

x3 on checking with the mechanical guage before doing anything else.

P2pastor

Same issues here. Low oil pressure at idle, losing coolant. I've verified the low readings with a mechanical gauge, replaced the sending unit, replaced the oil pump, and TODAY INSTALLED A BRAND NEW HEAD AND STILL HAVE THE OIL PRESSURE ISSUE!

Anybody else out there replaced the head and still have the oil pressure issue?

I'm wondering if the coolant in the oil degraded the bearings and that's where I'm losing the pressure? The engine rebuilder who I ordered the head from is not familiar with the 0331 issues, but couldn't understand how a cracked head could result in low oil pressure.

5150mechanic

If you run the oil/water mix long enough it will ruin the cam bearings first. I have a 2000, changed the head, low oil psi., changed crank and rod bearings & oil pump; low oil pressure,,, changed cam bearings (that were damaged/bad) . Now 20psi hot. If it has the miles do your self a favor and do a rebuild.

tjwalker

1. Low oil pressure should always be VERIFIED with a mechanical gauge. They can be rented from many big box parts stores. Failure to do so can result in the "chasing of your tail".

2. If you have verified low oil pressure on an 00-01 and you're using coolant, (having to add anti-freeze to your coolant reservoir) and you can't find a leak, the primary suspect is a cracked 0331 cylinder head. The #1 symptom of a cracked head is "unexplained coolant loss". Commit this sentence to your memory.

3. If you have a cracked 0331, coolant will get into your oil and eventually destroy your bearings, resulting in low oil pressure.

4. An overheating of the engine virtually guarantees a cracked 0331. Keep your cooling system well maintained!!

5. Anybody with an 00-01 needs to read the below thread. It is required homework. The key to the 0331 is monitoring coolant level and if the head does crack, catching it and resolving it early enough so that it doesn't toast your engine.

http://www.jeepsunlimited.com/forums...d.php?t=391831

cruiser54

I agree with wnjfirearms. This is simple and interesting:

http://www.jeepforum.com/forum/f19/4...fixed-1304679/

wjnfirearms

The article cruiser refers to is interesting and telling. Like I say, the simplest solution is the most common in many cases

Look at the orifice that the sender screws into. It's fairly small in diameter. The orifice into the guts of the sender itself is way smaller even. It doesn't take much to clog either of them and it doesn't take a neglected engine to have this issue. All it can take is a bit of anything crap wise to break loose and get to the orifice before it gets to the filter.

This reminds me of when my German Sheperd injured her lower jaw because she loved to carry around what amounted to nearly tree trunks in her mouth and the vet wanted to diagnose for all kinds of neurological issues and nonsense and all I could see were $$$ when nothing simple was ruled out. She totally pissed me off on principle. I took her to another vet and he found it was simply a sprain of her lower jaw as I suspected. Some inexpensive meds to promote healing and she was right as rain again by the next day.

Unless you have deep pockets and don't mind throwing money around needlessly, keep things simple before going complicated. It's way too easy to empty your checking account and still not fix the problem.

Then again, if anyone has that kind of money to throw away, please call me. I'll find good uses for it for sure.

cruiser54

I wonder if a guy could remove the sender, poke and probe with a piece of wire into the brass 90* fitting, then fire off the engine with a shop rag/old towel over the fitting and let the pressure expel the clog using an observer to tell him when to kill the engine. Then clean out the tip of the sending unit and see whatcha got.