Carabinerx

My oil pressure has been steadily dropping the past month, from 20psi hot idle down to 13psi. I found the oil adapter has a leak, but it's so rusted I cant get the t60 bit in to change the o-rings.

In stop and go traffic pressure rises up to about 18-19, but after any highway stints it drops back to 13. These are both after having been driving for hours.

I did an oil change to 5w-40 rotella t6, used a wix filter and cleaned the elbow to the oil sensor, seems to just drop straight to 13psi no matter how I drive now.

The leak isn't even that bad...no oil dripping on the ground, though there is evidence of it on the rear main and I burn about 3/4 of a qt in a month.

I'm supposed to drive 6 1/2 hours to Pittsburgh this Friday, and back on Sunday and feeling a little concerned about it. I wish I could get the damn adapter off, been spraying it with rust remover but it's hardly making a dent, and certainly wont be in time for the trip.

Any ideas or advice here?

tjwalker

I would highly recommend that you "verify" your oil pressure. Use a mechanical oil pressure gauge, which are available for rent (inexpensively) at many parts stores....call around.

Remove your oil pressure sending unit, temporarily install the mechanical gauge. Now get oil pressure readings to see where you are truly at. It's very possible that your oil pressure sending unit is starting to fail. It's an extremely common failure on the 4.0 liter engine.

I also have to ask the question.....are you using any coolant / having to add to your coolant reservoir? If the answer is yes, then because you have a 2001 XJ, a cracked 0331 cylinder head is not out of the question and if not resolved quickly, the coolant mixing with the oil can wipe your engine bearings in pretty short order and reduce your oil pressure. I'm not saying that is your problem, but would be remiss if I didn't include the possibility in my reply.

BTW, here are the oil pressure specs for the 4.0:

*Not less than 13 psi at HOT idle

*Between 37-75 psi OVER 1600 rpms

If you end up replacing your oil pressure sending unit, do yourself a favor and buy a genuine Mopar unit from Jeep for the best accuracy/reliability/mating with your factory gauge.

Good luck and be sure to let us know what you find out!

Carabinerx

@tjwalker thank you, yea a mechanical guage is at the top of my list right now. I actually did replace the sending unit last month, with a mopar unit -- forgot to mention that

dave1123

The word I got was premature failure of oil pumps on 4.0s is not uncommon. They seem to start loosing efficiency around 150K miles. I've heard this but not experienced it myself, but it is something I keep in the back of my mind. A slow dripping leak shouldn't reduce your pressure enough to make a difference, but a spraying one will. The pump's case is cast iron and will wear enough to increase the internal clearances around the gears and reduce the flow rate at low engine speed, causing low idle pressure in addition to the restriction of that banjo bolt in the adapter. I am SERIOUSLY going to look for a smaller filter that will screw directly into the block without the adapter. Then I'll just add a filter change between oil changes.

After saying this, my 2000 WJ 4.0 had gone 250K miles with the same oil pump, never showing any reduction in pressure. It always held 40 psi at idle hot and 55 at highway speeds. Before I pulled to because of a small rod knock, the valves only got louder without any low pressure symptoms. This engine even went thru a cracked 0331 head! Why do XJs and ZJs have pressure problems and WJs don't? How about TJs? The problems seem to be with a 4.0 that has that adapter and not with ones that don't. I don't understand this.

One thing that came to mind about removing that banjo bolt is to weld a nut to it and use a wrench on it. The heat of the welder should loosen the Locktite and make it easier to turn.

Carabinerx

Hmm, thanks @dave1123 I just passed 158k this weekend. It seems strange to be losing so much pressure over the course of 4/5 weeks, and I’ve had this leak for a little while and was still maintaining ~19psi. The pump seems like the next logical step, but would it degrade/fail quickly like this? Seems to drive fine, no weird sounds, the occasional high idle (750 instead of 500), there is a whistling that’s developed in the last couple days which I’m assuming is the exhaust manifold gasket going...I don’t believe either of these would be contributing factors, but maybe someone more knowledge than myself might see a correlation.

Password12345678

The high idle is most likely caused by a vacuum leak. You may notice that your cruise control is not working or the blower is stuck on defrost. Pop the hood and find where the whistling is coming from. It will most likely be a cracked rubber hose. Easy and cheap fix.

dave1123

It's supposed to idle at 750. 500 is a slow idle and won't keep the alternator charging or the oil pressure up. Cold startup should be 1000, dropping down as the 02sensors start to warm. After you find the vacuum leak, try cleaning the IAC.

Carabinerx

The whistle seems to come and go, didnt hear anything this morning. A cracked hose would be a lot better than the gasket!

It used to idle closer to 700, but after I cleaned the IAC and upgraded the injectors (once warmed up) it sits around 500+

Is that entirely governed by the IAC? I'll have to look if there's a way to change it.

EZEARL

Quite a few years back I had to clean my t/b and IAC after having idling issues. Solved the problem for about a month and had to replace the IAC. It had tested near minimum spec anyway. They do wear out. I bought an SAP (Standard Automotive Products) one from RockAuto and it's still doing fine.

Carabinerx

Gotcha, maybe I should just replace it. When I reinstalled it after the cleaning, my check engine light came on with an IAC code, but dissapeared after I recent the pcm for the new injectors. Probably needs a new one, haha

dave1123

You can test the TPS with a multimeter. disconnect it and set your meter to ohms. I don't remember which pins you need, but check the ohm reading from idle position to wide open. It should increase smoothly without flat spots or jumps in the readings.

Red1992XJ

Certainly get a mechanical gauge to verify. Also, there is a way you can add a T fitting so you can disconnect and connect the mechanical gauge without having to keep removing the oil pressure sender. (There is a thread on it here somewhere)

I would be a little leery of taking that far of a trip with a potential problem.

pnolans

Please disregard. I couldn't see how to delete this. Moderators: please feel free to. I answered my own question.

Thanks,

Pat

bluejeep2001

if you run a 1/8 tee fitting off the block where your sender is now installed you can have a mechanical gauge and the electric sender at the same time. why run such thin oil in a jeep with 100k + miles. run at least 10w-40 if not 15w-40 if its still low when verified by mechanical gauge then you have bearing issues... what's the pressure 5 min after cold start

dave1123

5w-40 is not a thin oil. Multigrade oils are designed with viscosity modifiers in them to basically work like the "w" number at cold temperatures, but act like the higher number at operating temps. That's a little simplified, but you get the picture. Besides, T6 is a synthetic diesel oil with high zinc content and high temperature stability. It will get darker earlier because it's designed to hold impurities in suspension and not let them settle out in the pan. Diesel engines are noted for oil turning totally black between changes because of the carbon produced in combustion.