Why is my oil so dirty already??

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Dec 31, 1969
I have a '90 Cherokee with the 4.0 liter inline 6 engine. It's been a bit of a project car for me over the last year or so, and it's just now getting to be a daily driver. It's got 98,000 miles on it, and the previous owner (my dad) rarely changed the oil...and allways used the cheapest oil he could find if he didn't take it to jiffy lube. The first oil change I did on it, I don't know how long it had been, but the oil was DISGUSTING! I could have used it to re-pave my driveway. (the last few years of it's life he cared even less for it than when it was new, so it had probably been in there 3+ years) Now, considering that, the engine still runs pretty good. I changed the oil, with 10w30 dino oil and a can of marvel mystery oil, and drove it about 200 miles before I noticed the drain plug was leaking. So, I put some Seafoam in the oil, drove it about 20 miles, and changed the oil and filter again...and the oil was pretty dirty. Now I've driven it about 100 miles since then (second oil change in 300 miles) and the oil on the dip stick is looking pretty dirty already. What gives?? Is my engine just THAT dirty on the inside? Or are there some other problems I should look for?
For as long as the old oil was in there, I wouldn't expect the engine to become piping clean with one treatment of seafoam and an oil change. Sounds like the present oil is just doing its job, cleaning and suspending the ugly stuff. I'd be inclined to use an oil that has aggressive detergents such as Chevron Delo 400 15w40 and change at 3000 miles. [ November 05, 2003, 09:27 PM: Message edited by: Kompressor ]
I'd change the air filter and tune it up right-off since it probably needs this anyway, based on your comments about neglect. When you remove the oil filler cap, what's it look like inside? That might answer your question right there. The fact that your dad used a "cheap" oil was probably of no consequence since all name brand oils have sufficient additive packages to prevent problems if regularly changed (yes, with a few exceptions like certain Toyotas, etc.). Sounds like additional detergent/dispersant treatments might be in order -- see the "Additive" forum for good advice regarding that. I'd venture that what you suspect is exactly what's happening -- yes, your engine IS just that dirty!... Get out the chemical "toothbrush and dental floss" Kompressor's advice on using a "diesel" oil is good. Perhaps, in the meantime while you're doing some short-term clean-it-out oil changes, use the very cheapest oil you can find, then switch to diesel oil once you see actual metal through the filler cap and can go "long" on oil changes. [Smile] [ November 05, 2003, 09:38 PM: Message edited by: TC ]
Ditto on the tune up idea. Buy a Haynes manual for that Cherokee. The Jeep 4 liter straight six is a pretty simple, solid motor. 98,000 miles is nothing for these if you take care of it. You may be able to remedy some/most of your dad's neglect but don't go broke trying every additive out there. 98% are crap. You can read about the whole lot of them in the additives section. After the additives and frequent oil changes to flush the motor I also endorse the diesel type oils. Chevron Delo, Mobil Delvac and Pennz Long Life in the 15w-40 weights are probably going to be your Jeeps favorite oils anyway. They tend to like a thicker oil. good luck, stay sane [Cheers!] [Patriot] [ November 05, 2003, 09:56 PM: Message edited by: GSV ]
Yeah, it's been "tuned up" along with alot of other things being replaced - mostly due to poor maintenance. [Roll Eyes] The dip stick is even stained to the level of the old oil. I guess it is just REALLY REALLY dirty inside.
Your Jeep sounds like a perfect candidate for Auto-RX. Frank will refund your money if you are not happy. 2 bottles as sprintman suggested given the mileage. [Cheers!] [Patriot]
Yeah...I'm going to have to take off the oil pan to replace the rear main seal, and the valve cover because I'm going to paint it, so I'll wait until after I replace those gaskets to really clean it out.
What I'd do: Pennzoil Long-Life Chevron Delo 400 Mobil Delvac 1300 All 15w-40 and available at Wal-Mart for $6/gallon. Oversized filter, believe the SuperTech part number is ST8A. This combo will be very inexpensive. Change every 3,000 miles for the first couple of times.
You are very lucky to find a Cherokee with such low mileage. My 1992 Cherokee has 189,000 miles on it and runs like a top. These motors are very rugged and the fact that the crankcase holds 6 quarts of oil doesn't hurt. The things that wear out on these motors are idler pully bearings, water pumps and all the belt driven anything. But these things go out at 100,000-180,000 miles, (normal for any car.) Replace that stock radiator with a 3-core Go-Dan radiator for about $120. delivered to your door.www.radiator.com-- It will never run hot after doing this. (The stock one starts leaking at any milage.) The 'new-process' transfer case seals go out also, so replace those when they start leaking A.T. fluid. Some guys have 350,000+ miles on their Cherokees and they still run great! In a short time this jeep should be a gem.
This August my brother purchased a 98 4.0 Wrangler that was a garage kept lease vehicle with 63000 miles. The lease aggreement required 3K mile oil changes at the dealer and all other required maintenance. They used bulk Pennz 10W-30 and a Mopar filter. I ran an AutoRx treatment with Mobil Delvac 1300s and then did the rinse cycle with Pennz 15W-40LL. The inside of the valve cover was pretty clean to begin with but I could tell a difference after the autorx flush. Now for winter I filled it with Schaeffers 10W-30 Blend and when spring hits it will get Schaeffer 15W-40 Blend. These 4.0s do seem to run smoother on 15W-40 oils. As for the radiator leaking well it happended at 65000 miles. I would recommend an AutoRX flush and then you should be set to go as these engines are bulletproof when taken car of.
Yeah, it still runs pretty **** good considering it got almost no maintainence in 13 years. The reason it's only got 98k is because it was used just to get my dad to work for about 5 years which was only a mile away. Poor old jeep won't know what hit it when I'm done, I have alot of performance upgrades planned. [Smile]
in my accord, my father who origionally owned it, changed oil every 10K. the oil always got dark quick....but after comming to this site and learning about auto rx....the engine is now clean and the oil only becomes a tanish color when 3000 miles are here. my dad also changed the oil filter every 20k with the coventional fram =)...now the car is running great...good job dad [Smile] car has 178 k for a 91 accord
4.0L engines are beasts. They can take a lot. I'm gonna try Auto-RX and i have 71K miles. This Jeep was dealer maintained by the previous owner's expense. I suggest you try the auto RX. Use a larger filter like the Motorcraft FL1A. It fits on my 95 4.0L.... i'm not too sure about the 90 4.0L since its not the high output version. I think the oil filter is on upside down.
The '90 model 4.0 uses a different filter than the '95; as a matter of fact, it requires metric threads. Not too many choices for suitable filters available. BTW, my '90 Jeep Cherokee with the 4.0 developed a rear main leak around 130K miles. I used Auto-Rx at around 150K, and it stopped the leak! It now has 168K with no leaks. Worth a try in your case.
Right before I change my oil, I typically add half a can of Marvel Mystery oil and drive a couple hundred miles. MMO must clean up the inside pretty good because the oil darkens noticeably after those couple hundred miles. I'm getting ready to put a truck in storage for the winter so I did that this week, added some MMO, drove about 200 miles then took it across the street for a cheapy oil change ($12.95 LOF-5w30 Kendall oil). I like to change the oil before putting the car up for winter and I'll change it once I take it out of storage and put a few hundred miles on, so DINO is just fine. I'm gonna try the Auto-RX on my sons beast (91 S-10 Blazer w/ 182k miles) next spring, but I've had good luck with Marvel Mystery oil. [Razz]
Talked to my dad today and told him the oil was already dirty again. He said "It's suppost to be that way". [Big Grin] [LOL!] [Dummy!]
That's funny! I can hear something like, "It ain't dirty 'til it's darker than my coffee." Marvel Mystery Oil...that brings back a memory. About a hundred years ago (maybe the late 70's), my mom's 1969 Mercury station wagon had a nasty lifter tick that wouldn't go away. Even with frequent oil changes (and all that detergent), it wouldn't stop, so we assumed it was a bad lifter and ignored it. A mechanic suggested MMO, and I thought, "Snake oil?...You've got to be kidding...It looks like ATF!" My dad tried it, and sure enough, no more tap-tap-tap after after a few days.
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