Hi yall. Im new to the neighborhood, hate to meet under these circumstances, but here goes: About a month ago, I bought a '00 xj 4.0l w/100k. It was love at first cruise! (Dodge is my usual drug of choice) Anyway, first week of ownership, no real problems. Now as these few weeks have progressed: started as rough idle once engine is warm and oil pressure all over the place (drops as motor warms up), losing gas milage, absolutely no power, and now using excessive coolant too. Last week it threw 3 TPS codes, so I replaced the TPS, and cleaned the IAC and throttle body (both had massive amounts of carbon build up). The new TPS and cleanup did nothing to fix idle. On a whim, I took it to a buddy to have the cooling system pressure tested, which failed miserably Im told. Just yesterday it threw 3 new codes, this time misfires (cyl 1, cyl 5, all cyl). Now Im irritated. Today I went and had a chat with the place who sold me the jeep. They insist that it CANNOT be either a head gasket or cracked head because they had just replaced both (head came from junkyard) right before they sold it to me. I presented them with my knowledge that I know now that this motor's original head as one of the flawed 0331 heads, which was crack prone, Im assuming that the "replacement" head is another one of he flawed 0331s. (These people also claim that the 4.0l is indestructible, that head statement is just speculation. Really?!) My buddy did mention that it was obvious that the motor had been apart, so these "honest" people may have done some work to it, although Im not sure I trust it was done right. Is it possible they messed up a head job and caused further damage? My sanity and temper depend on your guys insight! Thanks all!

 

I do hate to say it. But I think that you hit it right on the money about it having a bad head. If you got any kind of warranty on you XJ. I would have them do an inspection on it. If you remove the oil fill cap does it look like a brown milk shake under the cap. Also when you remove the oil fill cap take a real bright flashlight and look to see if you can see a crack in the head. A lot of times you can actually see the crack in the head. I there is coolant in the oil DO NOT keep running it. It can and will cause damage to the bearings and you will have to rebuild the engine real soon.

 

What torrez says is true. I ruined a perfectly good car by doing that. Not one of my brighter moments in my teens

 

The statement from them that the possible head statement is "speculation" is their defense, but a weak one. You are going to have to get some solid data to figure out what is going on. Testing is the only way to proceed here. I recommend the following.

1. Pull oil fill cover and look inside carefully with a good light. The 0331 head almost always cracks between cylinders 3-4 where there is a factory defect. With a hot engine, you can sometimes see the green coolant seeping through a crack, if there is one.

2. Perform a "block test" where you sniff the coolant for the presence of hydrocarbons. It is not a conclusive test, but a complementary one.

3. Perform a cylinder leakdown test. This may be the best test to diagnose if you have a cracked head. It requires specialized equipment, but is worth the money to have a shop perform this if it comes to it.

4. Run a compression test. This is NOT the gold standard to diagnose a cracked 0331 head, but it is a good "snapshot in time" of the internal condition of the engine and can snake out a bad headgasket. The compression spec. for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.

Good luck and keep us updated!

 

Thank you for the insight guys! Well the people I bought it from are working with me, and when I talked to them yesterday, they informed me that they did their own research and are conceding to the fact that there is a history of flawed heads in these years. Wow. Ya think if you are going to be in the auto business, you would know your vehicles inside out? But my best guess is that they knew, and werent counting on me knowing as well!! One last thing, if the head is indeed cracked, or even if its the gasket, why isnt there coolant in the oil? I know what it would look like...however the oil is very gas diluted! Related symptom? Or is this a whole new can of worms???

 

The cracked head is going to lead to running issues. Running temps won't be correct and such leading to fuel not being burned off. I wouldn't worry about any of that unless it still happens after they work on it again. Just make sure that they change the oil out when they fix the head issue and go from there.

Black89

 

Well, That is real good news. I hope that the do fallow through and take care of the problems. Just keep us updated and let us know how everything works out.
Good Luck!

 

Different can of worms. If the oil is indeed very gas diluted, there must be one or more fuel injectors stuck open at shut down causing raw gas to dump in the affected cylinders and flooding past the rings. Not good. If, in fact, you have bad injectors (as described), the PCM won't throw a code for them. The misfire codes would be the byproduct of this however.

If you keep operating the Heep with gas diluted oil it will eat your engine Mach Schnell.

Check your fuel pressure at the fuel rail fitting using a fuel pressure test gauge that you can rent (deposit return) form an auto parts store. You should see 49.2 +/- 5 psi. Without using a relay jumper switch to run the pump, you will have to place the ignition switch to RUN a couple of times without starting the engine, then check the static fuel pressure. If, by the time you get out of the cabin there is no fuel pressure indicated it means the fuel went somewhere (think injectors). If the fuel pressure is still holding at or near 50 psi it should take 5 minutes, or more, to drop to 30 psi. You may want to have a helper do this so you can watch the fuel gauge without interruption. This is not conclusive that the injectors are leaking however, a check valve in the fuel pump module may be leaking.

You said "why isnt there coolant in the oil?". Good question. It may not have progressed that far yet.

Edit: Don't forget that water is heavier than oil and it will be at the bottom of the oil pan. It's best to drain your oil and check it out. You need to anyway having fuel in it.

 

I could see (although it's a long shot) that a crack in the head that connects the combustion chamber of a cylinder with an oil passage would allow unburnt fuel to enter. So on the intake stroke a fuel/air mixture is drawn in, with the compression stroke and a misfire of the spark plug that fuel/air mixture will be forced into the crack, there-by ending up in the crank case.

Still a good idea to check that fuel pressure and all the injectors too.

 

Thanks all for the additional info on the fuel/oil issue..I will report back next week with the findings! Much appreciated!

 

Update for you guys: I got my baby back! They ended up doing a total rebuild, swapped out the crank, new bearings, the whole deal, the guys said the bearings were pretty wiped anyway. They put a remanned head on and they said the fuel/oil issue was bad injectors. So now my Cherokee is back and better than ever! Runs like a top, has power, and fuel and oil pressure are reading normal. I was told to change the oil in 500 miles, which I knew to do anyway because of the rebuild. My question, do you guys in your experiences with 4.0s have suggestions on a specific oil I should use in the future? I know some vehicles sometimes like one brand or another. My 83 Dodge for example, works best with Quaker State, but burns Pennzoil...Once again thanks for your insight folks!

 

GOOD to hear.

Oil choices can be a bit controversial but not filters. Use only a good one. Many here suggest WIX which are the same as NAPA Gold. One of the favorite oils around here seems to be Rotella T6(full synthetic). I run both the NAPA Gold filter and T6 in my '96 XJ(4.0) and my wife's '96 Blaxer(4.3).

 

Glad to hear that you got it taken care of you you got her back. As for the oil many including myself really do like to use Rotella for the higher zinc content which is recommended for our engines. But your preference may be different. Like EZEARL said you do want to use a good quality oil filter. The best for our 4.0 would be Mopar, Napa Gold and the Wix brands. What ever you do stay away from the fram filter and any other crap brand filter. Hope this helps.

 

As long as you change it on time and don't use a Fram filter, you'll be fine.

That being said, I use a Mopar filter and Quaker Defy 10W-30... High-zinc synthetic (50%+ synthetic) blend.