Low oil pressure?

I've searched and most posts are about high oil pressure, I have low oil pressure. The pressure only goes up to about 40. When idling it will drop down to almost nothing and the check gauges light comes on, if I rev it up a bit over 1k it'll go back up to the 1st or 2nd line. The gauge is steady and this is a constant problem. The oil is recently changed and not low at all. Any ideas? I'd think if the pump had a problem it wouldn't pump at all. Maybe the sender?

Thanks,
Mark

What year is your XJ? My gauge would do all sorts of wrong after I broke the pressure sending unit. Its scary seeing it at 40 psi. and then as your pushing 70 on the highway drop to nothing. I don't know much about these things(disclaimer), but on a Chevy, we'd hook up a manual gauge and check it out. At least 10 lbs. per 1,000 rpm means your motors ok. Also what oil and filter did you use??
- Mark

It's a 2000 XJ 4.0L automatic. The gauge acts normally, does not jump around. It sits around the 1st line while idling and eventually drops to 0 and makes the check gauge come on after idling for 5 minutes or so. It'll go up to 40 in the upper rpm range. I am using a fram oil filter and I don't remember what kind of oil but it's 10-30 i'm pretty sure.

I had the same problem on my '89 YJ. I ended up having a leaking head cover gasket, which was evidenced by oil trails on the block. Once I replaced it, the pressure went back to normal. Note that this was a 4.2L six cyl.

My 1997 TJ did the same thing, it randomly dropped pressure while driving. Turns out the OEM sender was sorta sketchy (that was the first thing the parts guy asked, has it been replaced?). I spent like $15 at the dealer and got a new one, took all of like 10 minutes to replace. Voila, no more pressure problems, reads dead on now. This was a 4.0 too.

HTH,
Chris

mine is a 2000 2wd 4.0L XJ, at idle it is about 30psi, if I am accelerating it goes to about 52psi, using synthetic oil

Have you put a manual oil pressure gauge on the engine and double checked the pressure? That would be the first thing I would do. I have seen quite a few 99 and up XJs that have a cracked head that leaks coolant into the crankcase. The coolant leak is slow enough to not cause the oil to look lika a chocolate milkshake, but enough to damage the bearings. I have personally changed about a dozen heads on the 99 and up 4.0l engines in the XJs, WJs, and TJs and have had to change the whole engine assy on a few more if the customer drove for too long without noticing their coolant level dropping without any external coolant leaks.

That being said, if you don't have a manual gauge to test it with, try changing the sender unit and recheck what your gauge is saying.

Bryan

oh boy, so how much does one of these new heads cost to put on the jeep? I have noticed the coolant level dropping a bit lately and could never find a leak. Also, the oil level might have actually gone up a bit but I can't really be sure. How can I test to be sure this is the problem before I rip the whole head off?
Thanks!

The oil pressure sending units on these Jeeps are nortoriously cheap. Mine would tend to read too low. Went out on my '98 at less than 40k miles. They are so cheap just try a replacement and i bet that will do it. Do the dealer. Prob are not yet available for your 2000 aftermarket anyway.

Judd W. VA said:

The oil pressure sending units on these Jeeps are nortoriously cheap. Mine would tend to read too low. Went out on my '98 at less than 40k miles. They are so cheap just try a replacement and i bet that will do it. Do the dealer. Prob are not yet available for your 2000 aftermarket anyway.

Click to expand...

Good advice. I didn't want to jump the gun and tell you that you need an engine. Just start at the basics. If you don't have a manual test gauge for oil pressure, try replacing the sender. Cheap and easy test. Try using a good quality (mopar) oil filter too.

If you are losing coolant, most of the heads crack right below the oil cap. Just remove the cap and look straight down onto the head. Adding coolant tracer dye and a UV inspection lamp makes it easy to see the coolant leak, but you can see just as well with a flashlight. I would think the more likely source of the coolant loss is the thermostat housing and/or water pump.

As for cost, I think a bare head runs close to $600 at thr dealer.

Bryan

Well, I changed the oil, that didn't help the oil pressure, i changed the oil pressure sender, that didn't help. I took a trip this weekend (about 200 miles) and went through a gallon of antifreeze. I changed the oil again and there was definitely antifreeze in the oil. I guess it's time for me to replace the head. I'm worried that I'll spend all this time/money on this head and the rest of the motor could already be junk. It has 75,000 miles and I noticed the coolant starting to disappear about 1000 miles ago. Should I just swap in a whole new 4.0L or maybe a bigass V8 instead (will a hemi fit?)!!!! If I'm gonna do it I want to do it right the first time and be done with it. What a piece of shit, cracking at 75,000 miles. I have changed the oil religously and never did anything harsh with it and this is the thanks I get.

What do you guys think??

Mark

I replace my motor when a alternator bearing went bad Actually it was a mis-diagnosis by the local shop, they said it was going to throw a rod, so I took their word for it and dropped in a new engine.

A few of the oldschool mechanic/car types I work with suggested strongly I not do a bottom end rebuild since the bottom end would be nice-new-and tight, whereas the head's would still be worn. Could cause some problems, so that's just my .02 worth.

If you've got the time and funds to do it, I'd say go ahead an replace it. I tool the oppurtunity to out in M.O.R.E. motor mounts, GDI 3 core radiator, Borla header, etc. while the engine was out and everything apart. Plus, I learned a crapload about my Jeep and enigne systems from doing this.

Chris

Sounds like to me, the water in the oil messed up your bearings(Explaining the low oil pressure). And if this is the case, all you may need to do is replace the rod bearings...mains may be ok) if the mains are shot then replace/rebuild is prolly needed. And if you do choose this you may want to look into a used engine, maybe one with 40 or 50K on it from a junkyard. I mean for $500-600 its better than $1100-1200 for a rebuilt deal, unless you just wanna rebuild it yourself. Just a suggestion. Either way good luck!

Too bad all the basic checks didn't help out. I would definately get a whole engine. The problem you are going to run into is that you may buy another crack prone head and have the same problem again. The 00 and 01 engines are different than previous years and finding a good engine might be a problem. If it was my money(which it isn't), I would get a brand new updated head and a remanufactured short block from the dealer and drop them in as a unit. Mopar doesn't offer a complete reman engine due to the fact the heads seem to crack easily. Just have a machine shop clean and swap the valves and springs from the old head onto the new head.

Bryan

you already stated a new head runs about $600, what does a reman shortblock cost, $1,000??? Plus I'd need at least a gasket kit, $200?? That's around $2000 including some machine work I'm sure that will be needed. Am I close on price? All this is assuming I'm doing my own labor and don't screw anything else up in the process ! For this kind of money there's gotta be a better solution than to be right back where I started hoping the new head doesn't crack. I plan on keeping this jeep forever, it is a 2000 and the body is mint. I know I'll get at least another 75,000 on it. Will I have to worry about the head cracking again or did they update the design? What about a newer 4.0L out of a tj, are they the same? Thank you guys for all the help, I'm just really pissed at this stupid jeep right now and want to make the right decision!

Mark

Too much oil can cause low oil pressure.
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Last year I got a 2000XJ from a dealer and it had the exact same problem creep up after a day of driving. It was a simple fix. They had filled it with about 1.5 quarts too much oil.
Try draining it to the low end of the fill range.

The oil level is right under the full line, plus this won't help the coolant in the oil problem.

OK did some checking, found that the reman short block retail price is $2000, the new head retails for $460. I also found out the only years that will interchange are 00 and 01 XJs. The 99 TJ block is the same, but the head is different than yours. 99 and older XJ 4.0l heads are different than yours too. 99 and up WJs and 00 and up TJs all have the alternator and AC compressor mounted differently than the XJ and have different mounting holes and required brackets. They moved the alternator to where the AC comp was, and then moved the AC comp to under the PS pump.

You have somewhat limited options on what to do. Since you say you plan on keep ing your XJ forever. My advice to you would be to buy a new head, pull your engine and send it all to a machine shop for an overhaul. I would think that you would still pay less than $2000 for the rebuild considering you are supplying a new head.

The other way would be to buy a used 00 or 01 XJ complete engine and then replace the head. Maybe you can find one that has the head replaced already? The only way I have seen to tell the difference is to remove the oil fill cap and look down onto the head itself. The updated head will have the letters TUPY cast into it between the #3 and #4 exhaust valve springs. This is exactly where the original head cracks too.

The part numbers I found are R5013116AB for the reman short block, and 53010334 for the new bare head. I would call your local dealer and see what they would charge for these parts. The prices I quoted were suggested retail and most dealers will charge more than that.

Good luck.
Bryan

what about getting a complete engine from a 02 or 03 tj and swapping it in. Are the motor mounts and tranny mounts the same. If I have all the new brackets for the accessories will I still run into problems as far as moving hoses and wires? It sure looks like no matter what I'm gonna be spending a crapload of money. How long do you think my motor has before it blows up and what signs will I get when it's ready to die?

Thanks again for all the help!
Mark

Moving the wires and hoses wouldn't be impossible, just time consuming and possibly expensive. You may need some custom AC lines made, and also the TJ runs the fan off of the water pump, so you may have problems running the fan. The TJ and WJ setup is quite a bit of different than the XJ. But other than that, the engine block itself should bolt right in. Spend some time searching around for a good used engine if you want to keep the overall costs down. Maybe just get a good low mileage engine and replace the head later on before it cracks.

When will it blow up? No idea really, but it should start making some sort of a knock or rattle noise before it goes for good. Try some radiator stop leak(not the aluminum type) and some 20-50 oil untill you can get this issue resolved.

Bryan