another Jeep 4.0, what oil is best for me?

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Peoria, Arizona, United States
the info with my motor/driving habits and such.

first i must say that my motor is a mystery. it has reoccurring issues that no one is really able to figure out. so a rebuild may be in store...

the motor has 325,500 miles to date, original motor,tranny, everything is original, no rebuilds nothing. as long as I can remember I have used Mobil 1 full synthetic 10w-30, I recently obtained the cherokee from my dad (it is a 1999 by the way) from what I know he has always used mobil 1 products and I would like to keep it that way. he has used different weights but the last 100k for sure has been 10w-30. every now and then I can hear a knock/tapping noise which i am hoping isnt from a lifter, but with this many miles...

my dad said it really has always made that noise and it isnt anything to be worried about, (he works on high end race cars so I'm trusting this advice) other problems are it having a messed up exhaust (leaks from header as well as multiple places down stream) it has a random misfire that occurs when you rev it to high for to long, which is cleared up by, you guessed it, reving it even more lol. recently I have put in Lucas Oil heavy duty oil stabilizer, I heard that stuff was junk so I stopped, on my last oil change I used a silver can from auto zone, it was simply called engine restore, apparently it eats all the sludge and from what I experienced it gave a smoother idle literally 5 seconds after start up, and the throttle was a lot smoother and responsive. Is this stuff worth continuing use?

i live in arizona where the summers can see 120+ degrees, and the winters Im up early in low 30s, I also head up to the snow often. my stepmom who put the first 200k miles on it drove it like a race car, she has road rage issues...my dad put on 50-70k after that and he drove it easy, then from there to here i try to drive it easy, but i do get on the gas quite a bit. id have to say most of my driving is highway/freeway at 75-80mph. although I do go through lots of stop and go to get to the freeway and sometimes sit in stop and go on the freeway.. I use fram tough guard filters, I also heard these were junk. they are known to cause oil pressure issues, but for others they are perfectly fine, I have the dummy guages so I have no way of monitoring my oil pressure, do you think I should switch to a higher end filter like Mobil 1 filters? the only thing I have to say is, the filter I dont care what brand I use, the oil I want to continue using Mobil 1. do you guys think i should switch to extended guard, high mileage or keep it with the regular stuff, any weight suggestions? hopefully only have to see one more AZ summer then I'm off for the air force next year.

oh also, I do change the oil every 3-5k, the longest I have gone personally without a change was 7k. the rear main leaks and I am always adding in more and more fluid so at the time I wasnt to worried cause it was getting fluid often...
 
Since you'd like to keep using Mobil 1, I'd suggest the high mileage since it's leaking. Your 3-5k interval seems too frequent to me for a synthetic though. With that interval any PCMO should do fine.
 
I would leave out the restore, if a good syn has been used adn changed appropriately there will not be sludge. A hm synthetic is what you want, if it starts to leak excessively then rotella t-6 or a good conventional hm is the way to go.
 
Fix the leak and use Mobil 1 HM oil. I think you can easly go to 7,500 miles on this engine with the oil you use. I did UOAs on my 95 GC and used Mobil 1 10w30 and Fram "Orange can" filters. Sold it running great at 225,00 miles. I replaced two rear crankshaft oil seals during this time. Ed
 
You might try Auto-Rx, any engine whith that many miles should benefit, but the instructions should be followed. Then back to a high quality synthetic 10W30 oil. If the engine has a waste spark ignition system its picky about plugs.

Don't forget the transmission, transfer case and both diffs.
 
thanks guys, the tranny fluid will be changed here today, I'm worried about that because my dad being the amazing mechanic he is, didn't know it had a tranny filter.... luckily he was very consistent with changing the fluid, I have some mobil 1 stuff, not sure exactly what it is but it is supposed to be for any transmission? my dad brought it home, said they ran it for a few miles in a race car and had to change out something so they put in new fluid when sowere done. not sure the story just know its pretty much brand new and free, bought a filter as well..

if I have enough fluid left over I will do the T-Case fluid, this uses ATF if I remember right? please correct me if I'm wrong, not sure if there is a seal for the t-case either, I do know that it hasnt been changed in for ever. I did the differentials with mobil 1 75w-90 about 15k miles ago. there were no shavings so I'm glad about that. everything looked to be in tip top shape in them.
 
Only use Dex/Merc III or equivalent for the XJ tranny. Some have experienced slipping in the AW4 with other fluids. For the diffs you can run either 75w90 or 85w140. The heavier might be better since you live in Arizona.
 
unfortunately I'm on a college budget and at the moment that means I have a grand total of 2.94 in my bank account lol. the ATF was free, let me go grab a quart and see what it is...its mobil 1 multi vehicle formula, synthetic, Dex/Merc Mercon V equiv to Dex III

the mobil 1 75w-90 was on major sale so I picked up some of that, later I will use a thicker weight, not to far off from another diff fluid change.
 
I would quit dumping whatever comes across your mind into the crankcase, and reving the [censored] out of it or it probably won't see 328k !
the miss is probably simple maint.
you should ask about it over a www.jeepforum.com under the XJ section.

your tick is possibly just your leaky manifold mixed with the normal 4.0 tick.

I would just stick with your mobil or run Rotella T5 10-30 (my personal fav.)
witha puralator PUREONE, p/n PL14670 they are on sale @ AAP for $5
your XJ will probably go to 400k with a tune up

as far as the diffs I think the XJ's call for 75/140 syn, and jeeps are VERY picky about there fluids !
 
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To the comments about shell rotella t6

I think Mobil 1 TDT would be better since the thread starter wants a Mobil 1 product.

I personally run Mobil 1 TDT in my 4.0 jeep and absolutely love it. No tick at all, but I do only have 75k miles
 
as far as the issues with the random miss fire, I have asked many, many times on jeep forum, I am regularly active on there, I have asked on NAXJA, I have asked on Expedition Portal, I have asked my dad (again, he works on high end race cars) I have asked many people he works with, I have asked many many many many mechanics and short of tearing everything apart and replacing a ton of stuff absolutely no one had a clue as to what the issue is. the reving lasts for a total of 10-15 seconds, no big deal really. I've already replaced most of the ignition system, changing the coil next to see if that helps. when I do maintenance I change the oil, oil filter, spark plugs wires cap rotor seafoam through the TB and fuel tank, clean TB, air filter, the miss isn't just due to poor maintenance, if it wasn't meticulously taken care of I wouldn't be at 325k lol...

on the upside, replaced the tranny filter and for the miles it has the internals looked spotless. we were impressed, no sludge at all, no shavings. the filter which was the original looked brand new..

anyways dealing with the original post, I will continue using 10w-30 mobil 1 but i will try the high mileage stuff, just hard to track down the 5 quart jug at auto zone... I will stop with additives short of the Auto Rx that was mentioned by Donald, I may give that a shot. thank you guys for the help. I know there is a ton of debate on what should and shouldn't go in a 4.0 which in my mind seems redundant to an extent, these motors are tanks and love the abuse
smile.gif
I'm tempted to keep up the regular OCI and see how far this motor really goes before a rebuild using only Mobil 1 oil.
 
as far as the issues with the random miss fire, I have asked many, many times on jeep forum, I am regularly active on there, I have asked on NAXJA, I have asked on Expedition Portal, I have asked my dad (again, he works on high end race cars) I have asked many people he works with, I have asked many many many many mechanics and short of tearing everything apart and replacing a ton of stuff absolutely no one had a clue as to what the issue is. the reving lasts for a total of 10-15 seconds, no big deal really. I've already replaced most of the ignition system, changing the coil next to see if that helps. when I do maintenance I change the oil, oil filter, spark plugs wires cap rotor seafoam through the TB and fuel tank, clean TB, air filter, the miss isn't just due to poor maintenance, if it wasn't meticulously taken care of I wouldn't be at 325k lol...

on the upside, replaced the tranny filter and for the miles it has the internals looked spotless. we were impressed, no sludge at all, no shavings. the filter which was the original looked brand new..

anyways dealing with the original post, I will continue using 10w-30 mobil 1 but i will try the high mileage stuff, just hard to track down the 5 quart jug at auto zone... I will stop with additives short of the Auto Rx that was mentioned by Donald, I may give that a shot. thank you guys for the help. I know there is a ton of debate on what should and shouldn't go in a 4.0 which in my mind seems redundant to an extent, these motors are tanks and love the abuse
smile.gif
I'm tempted to keep up the regular OCI and see how far this motor really goes before a rebuild using only Mobil 1 oil.
 
10 seconds of high rev is QUITE substantial for a 4.0 ESPECIALLY with those miles on it...........think about that count 1.1000, 2.100, 3.1000-10.1000............to rev a 4.0 like that is insane, that thing should hardly ever see 3000 rpm. lo rev, lo end torque.

as far as the miss, how do you know it's a miss, have you tried a new TP sensor ?
 
Agreed with wsar10, doesn't the 242 redline at about 4k?

I'd fix the leaking exhaust manifold and take it from there. I've done the one on my '94 and it took me a full day. You and your dad could probably knock that out in an afternoon. That'll solve your loud tick (it's especially loud right after startup right?).

When does your miss occur? Is this only when your doing the 10sec revs or under normal driving also? Did the '99's have an external canister fuel filter or an in-tank sock?
 
another thing , are your plugs OE spec.....Champion copper cores.
The 4.0 is quite picky about plugs...

and BTW you said rotor and wires.....I thought 99+ used coil rail setups ?

My WJ has the rail setup.
 
Hello, Sis' 1999 4.0 liter has a cap, rotor and wires. 159K and going strong. Can't say the same for the cheap air conditioning hardware. Fuel filter is in the tank on her's. Kira
 
with that kind of miles, maybe the distributor is shot, allowing timing to advance to fast? I'm sure the springs for the advance weights are probably weak by now, not to mention the bushings possibly being shot. I know, its a stretch, but if replacing all the other ignition components hasn't fixed it...? Timing chain is probably pretty well stretched too. As far as oil, I've heard lots of people with the 4.0 say that rotella t syn. 5w-40 or the Mobil 1 TDT runs great in these engines, they seem to like a 40weight better.
 
let me try and answer all your questions..

I know it is a miss because 1...its miss firing lol. and it throws multiple codes. miss fire in cylinder 1, sometimes it will say cyl 2 or 3, or random miss fire in multiple cylinders. oddly, the misfire only occurs at idle, when at any RPM above idle it runs excellent. (I have new injectors so these are not the issue and I have tested them as well as the old ones to make sure of this) the Distributor has not been replaced just the cap and rotor, I am testing my coil soon and most likely just replacing it just because it should be done soon since it is the original, if that doesnt help i will look at replacing the distributor.

redline on a 4.0 is more towards 5,500 i believe, I don't have a tachometer but have seen others. I know you are all just concerned about the motor and I understand where you are coming from but when I get a misfire from passing someone on the high way or getting on the throttle just a bit to much, it is highly irritating. it shouldnt happen, it happens all to often and id rather rev it up a little for a few seconds than deal with a miss for the next 100 miles. literally the whole jeep shakes at stop lights like its some kind of cammed out hot rod. obnoxious and it runs super rich, fumes are horrid...

when I rev it to clear the miss i would guess it is about 4k MAX that I rev to, the miss occurs under normal driving conditions when downshifting on the highway to pass a vehicle. the higher revs cause the miss. it used to be that even if I hit 72 mph and up it would cause the miss but that stopped after I changed the cap and rotor when I first got it from my dad.

have not tried a new TP sensor but that is on the list when I get paid at the end of the month as well as a new exhaust manifold. my theory on the situation was that the exhaust leak was causing the O2 sensor to read I was running lean so under higher revs the ecu dumped to much fuel to compensate causing it to run rich which in turn caused the miss. this theory was backed up by fuel on the spark plugs. but it is just a theory... also the tick has been when the motor is fully to running temp. it cleared up after I went camping though, havent heard it since, maybe climbing the hills cleared something out?

i do run Champion OEM spec plugs, wont run anything else, in 00 they switched to coilpacks..

fuel filter is the little pick up sock in the tank as well as another filter in the tank in the sending unit. one day I would like to run just braided steel fuel line so I can put in an external filter. but that will cost me, and I havent made fuel lines in a year or two so i need to freshen up on putting them together..

@Kira, my motor is amazingly strong for 325,500 miles, its all external parts causing the motor to have hiccups here and there. and I fully understand what you mean by the cheap A/C components..

I hope to god the timing chain isnt stretched. I hope to run the motor as long as i can before having to rebuild. hopefully that will be AFTER i have spent a few months in the USAF so I can pay to rebuild when it gives out. then 4.7 stroker will be built. I think I got all the questions, I tend to babble a lot and I apologize, just want to make sure all the info is presented.
 
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