How I Finally Fixed The ‘Jeep Cherokee From Hell’ That Broke Down 20 Minutes After I Sold It To A Nice Lady

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Last night I found myself in a dumb situation only I could have gotten myself into. I had sold a beautiful 1991 Jeep Cherokee to a nice Chicagoan named Tracy, who only managed 20 minutes of her 4.5-hour drive home before her new vehicle blew up. I took the Jeep back, promising Tracy I’d bring the venerable 4.0-liter engine back to life. She took my word for it. She believed in me. She ditched all of her other vehicles, and was now depending on me, giving me a deadline of June 14 or else she’d be carless. Last night, I realized that today I’d be flying to California to drive the 2023 Ford Bronco Raptor, meaning I had to fix the Jeep right now or Tracy was screwed. I wasn’t going to let that happen without a fight.

 

I write to you utterly fatigued from a cramped airplane on its way to Palm Springs, where I plan to off-road the crap out of a 2023 Ford Bronco Raptor. I’ve got a half-inch bloody gash in my left pinky, oil underneath my fingernails, and — though the woman sitting next to me hasn’t mentioned it — most likely a light smell of ethylene-gycol-based engine coolant emanating from my pores. I know I look like shit, my body definitely feels like shit, and yet somehow I’m on top of the world right now — not because of the Bronco Raptor, though that’s likely to be epic, but because last night I broke out every weapon in my toolbox and finally slayed the mechanical menace that is my beautiful 1991 Jeep Cherokee five-speed.

 

The overheating episode shortly into Tracy’s drive home had warped and cracked the Jeep’s cylinder head, killing compression in four of six cylinders. The vehicle ran on the remaining two, but it released a sound so traumatzing that I was forced to discard it from memory.

 

I zipped a cylinder head off the parts engine sitting in my garage, sent that into a machine-shop to be checked and shaved flat, and bolted that lid onto the exposed iron heart nestled between the shock towers of a truly gorgeous but thoroughly flawed AMC-designed box-on-wheels. Unfortunately, despite the engine now running well with its new head, the motor continued overheating and appeared to be gaining oil. I feared the engine had cooked itself during Tracy’s short drive and the block was now cracked.

 

There’s a reason why I feared the worst. I’d seen these exact symptoms before: A slight increase in oil volume on the dipstick accompanied by chronic overheating. And on all occasions, I’d sent an oil sample to Blackstone Labs, who told me that indeed, there was coolant in the oil. Check out these three Blackstone reports from a 1992 Jeep Cherokee, a 1995 Jeep Cherokee, and a 1996 Jeep Cherokee:

 

790c814f Df0b 4aff B017 92b1a0de53b7 3862b7da Ddd2 4ca1 9b55 5f2fb18ac3a3 38871763 Ddc8 4d6f 8160 Aafde100f714

 

All of these Jeep Cherokees ended up requiring new cylinder heads. But since I’d just replaced the 1991 XJ’s head, it wasn’t a stretch to take the overheating+gaining oil symptoms as a sign that the block had been compromised.

 

I’d pressurized the cooling system with a hand pump, and found that there was a slight leak (the pressure shown on the gauge dropped slowly). But I noticed no obvious drips, so perhaps it was internal? A cracked block would explain this pressure drop, and it would explain the overheating and the increase in oil level. But why was the engine making good compression? Couldn’t a cracked block compromise this? Why wasn’t there any steam coming out of my exhaust? Why was this increase in oil not accompanied by the signature milky consistency of a water/oil mixture? Why didn’t my block testing die detect any combustion gases in the cooling system?

 

I was still not convinced I had a block issue.

 

I thought about this Jeep all day yesterday when I really should have been writing/editing/running this business. I asked myself two questions. The first was: Am I 100 percent sure that the engine is gaining oil?

 

After installing the new head, I’d run the engine and noticed the oil level was elevated well above what six quarts tends to read on a Jeep 4.0 dipstick. But then again, I had poured some Marvel Mystery Oil into those cylinders, and some might have gotten into the crankcase. To get rid of that factor, I then conducted an oil change, but since I feared coolant was getting into my oil, I didn’t want to waste my good stuff, so I just grabbed some spare jugs I had sitting around. I used an old gallon jug of Rotella 10W-30 to measure out six quarts of cheap lubricant, but had I been precise? Was I truly 100 percent certain that this engine was gaining oil?

 

On top of that, since the oil didn’t look milky, could that have been fuel in the oil? I poured some fuel injector cleaner into my gas tank, and revved the living crap out of the engine. Accelerating that little Jeep made me realize just how magnificent the machine is. There’s just so much power and torque in just a 3,350 pound package; when this engine debuted in 1987, it must have blown people’s minds.

 

The second question I asked myself yesterday when I was daydreaming during work hours was: Why is the Jeep only overheating under certain conditions? It seemed that high-speed highway driving and idling were the worst-case situations. The former involves lots of engine heat rejection, the latter involves little coolant or airflow.

 

As I’d previously had issues with coolant temperature sending units on both Jeep Cherokees and Grand Cherokees, I dropped the $8 on a new one to make sure i was at least getting the correct readings on my gauge. Deep down, I knew the sending unit wasn’t the problem, because the temperature gauge was reading right in the middle under medium-speed, low-load driving conditions — especially when the revs were above 2,000 RPM. If the needle reads appropriately under not-particularly-taxing thermal conditions, then the sensor is probably doing its job, and the issue is actually with the system’s thermal capacity.

 

My soccer game on Monday night had given me a lot of information. I’d driven roughly 40 mph on back roads the whole way home, and the needle stayed firmly in the middle, only elevating when I stopped at my house and let the motor idle a bit. “This cooling system’s ability to reject heat seems to be compromised,” I thought. Sure, a cracked block would prevent the system from reaching its 13 PSI pressure, and could cause the vehicle to overheat, but the pressure leak wasn’t really that bad; I was able to pressurize the system with that hand pump, and the needle remained at 13 psi for quite a while before dipping down to 12. I’d driven a Willys Jeep across the country with a cooling system pressure of fairly close to ZERO PSI (there was a little leak in the radiator), but as long as I kept the rad full, the engine never overheated. I’d had pinhole leaks in radiators before, and those engines still stayed cool as long as they had water (“water,” by the way, is what people in the auto industry call engine coolant, by the way) in them.

 

More importantly, as I sat there at my house at 11 PM after my soccer game on Monday, with the AMC straight-six idling and me staring at the gauges like a weirdo, I slid my heater lever to the right and immediately felt those glorious joules that were once contained in gasoline blow through my vents. The temperature needle dropped to the middle. Hmm.

I thought about all of this yesterday after work when I realized that I’d be returning from my Bronco Raptor trip the last weekend before Tracy’s deadline. There would be no time to continue diagnosing the Jeep when I got back. Tracy needed a Jeep by the 14th or she’d be walking, and I couldn’t drive to Chicago during the week due to work. I had to deliver this Jeep to Chicago as  soon as my flight landed from California, meaning I understood last night that I had to fix the Jeep RIGHT NOW. That was not the greatest realization, I will admit.

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I ordered a radiator at about 6 PM, picked the plastic-and-aluminum heat exchanger up from the store, and began installing it. In my head, it was plausible that the oil increase on my dipstick had been either a leaky injector or just me being imprecise in my measurement, because in the past couple of days (including my drive to and from my soccer game) the Jeep appeared to have gained no oil whatsoever. As for the overheating, I reasoned that if all it took to keep the temps down was a little bit of assistance from my heater core, then maybe a more effective radiator would do the same. So I was praying that my only issue was radiator-related.
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A reader named Jeremy had messaged me on Instagram to see if I wanted to meet up, as he was in town from Toronto. We’d agreed to go to a bar, but I switched plans on him. He generously came to my EPA Superfund Site and assisted with my radiator replacement, which would end up costing me a reasonable $135 in parts, all told. The job took about two hours; I removed the entire fiberglass header panel (which contains the lights and grille), took off the upper radiator support beam, undid the coolant hoses from the radiator, removed the electric fan, unfastened the mechanical fan shroud, and plucked the old radiator right out. It appeared to be in fine shape, but it also looked to be the original unit (based on the Chrysler stickers present). That’s an old heat exchanger.

[Editor’s Note: I’ve seen David’s place in conditions of disarray that make a recently-bombed recycling plant look like Martha Stewart’s lakehouse. If David is saying he doesn’t want someone to see the condition of his house, I’m not sure I can imagine what that could mean. Is it crawling with filth-snakes? Knee-deep in cheese, mold, and mud? Did he just start shitting onto newspapers on the floor? Who the hell knows. – JT]

I had to drill into two of the brackets on the new radiator to make it fit, but — thanks to Jeremy’s help lining the bottom mounting posts up with the holes in the lower radiator support in the Jeep’s unibody —  the installation job was largely drama-free. At around midnight, we had the cooling system back together and were pouring gallons of antifreeze into the system.

Then we hit the highway, which was empty at one in the morning. I punched the accelerator pedal until the Jeep was driving 75 mph, generating lots of heat from that 4.0. Then I waited for that needle to rise from its center position, slowly but surely. But it refused. It sat there, unwavering. I hammered the gas pedal a bit harder, but the needle remained pointed at 210. I then pulled off the highway and idled the Jeep; this is typically a taxing thermal condition because all the heat that the engine creates in order to propel the car at high speeds still needs to be rejected (it’s not an instantaneous process), except now you’re at idle with low water flow and low airflow.

The Jeep didn’t give a damn. It continued to run at its normal operating temperature.It wasn’t the relatively cold ambient temperature outside giving me false hope, either; the prior cool night, after my soccer game ended around 11 PM, I noticed overheating at idle. But now, no matter how long the Jeep sat stationary, the new radiator had no problem transferring that engine heat to the incoming air. My overheating issue was gone. It was a clogged radiator.
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In retrospect, the coolant coming out of the old rad was pretty damn brown, so maybe I should have known. But I’d been burned so many times by overheating Jeep Cherokees gaining oil due to cracked engines that it was impossible for my mind not to go there.

After four years, the XJ from hell has been rescued. Now it’s time to get rid of it as quickly as I can before it tries to ruin my life further. I wouldn’t be surprised if it performed flawlessly for Tracy for years to come. I truly hope it does.

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75 Responses

  1. David, you know I love you but I’m gonna have to see some proof of a radiator clog before I consider this well and truly sorted. When one has done as much tail-chasing and wheel-spinning as you have done troubleshooting this problem, you don’t get to declare victory just on the basis of a differential diagnosis. I want Tracy The Nice Lady’s Cherokee to be fixed as much as anyone, but I also want to see you cut open that old radiator and show us the blockage. I also want to see a followup article in a few weeks, telling us that all is well with Tracy’s Jeep. I myself have been battling a not-dissimilar issue, and every time I think I’ve got it licked, it comes right back to bite me. I’m rooting for you, I want you to be victorious, but I think a victory lap is a little premature just yet. Show us that you’re right!

  2. Told ya it was something simple! I didn’t mention radiator because believe it or not, you really are supposed to do all those things before condemning the radiator unless you have OBVIOUS radiator failure such as a leak or obvious bulge. Discoloration isn’t enough to be obvious radiator failure. The amount of Coolange(TM) Sluj(R) in 4.0’s means green + clear = toddler diarrhea brown.

    You just did the replacement job. You know exactly why we avoided condemning a radiator prematurely. Especially since you had to try the petcock first to try and avoid hose replacement.

    The absolute worst trap any mechanic can fall into is second guessing their work infinitely. Absolutely if a mechanical repair doesn’t fix the problem, you double-check your work. But you have to stop questioning your repair if it tests okay. The issue wasn’t the work you did, so you have to go back to diagnosis with confidence and understand that it’s a complicated machine and you’re only human. Multiple problems not only can be, but commonly are present.
    In other words, “I didn’t repair the vehicle incorrectly, there is another problem present which I could not see without repairing the first problem.” You could not have possibly seen or diagnosed a partially plugged (it was a partial, not a full) radiator without first replacing the cylinder head, water pump, and ruling out every other potential cause such as faulty sensors and broken fans.

    At this point, the Jeep has been gone through with a fine-toothed comb. The only real failure I’d expect for the next 50-100k miles with proper maintenance would be the fan clutch if it wasn’t replaced before, or possibly the aux fan. That’s it. Okay fine, maybe a transmission solenoid pack.

  3. Congratulations! There is no better feeling than taking that victory lap and realizing that it really is fixed! The satisfaction of bringing an old car back to life and sending it on its way, confident that it will serve its new owner for years to come is awesome as well!! Good stuff! Now, give that Raptor a good thrashing for the rest of us!!

  4. Glad it is fixed.

    The downside is I have the image of Torch’s description of David’s house in my mind. I guess that is revenge for the Torch with Puppies image. Well played sir, well played.

  5. David, I knew you could do it! I think you, like me, are powered by spite, stubbornness and sheer force of will.

    I think one of the commentors mentioned the radiator yesterday, but it always seems to be the basic stuff that bites a guy. Sometimes you just need to step back and assess.

    1. Yeah I used to be that guy. I would go out of my way to find the brick wall, I would stubbornly thrust my Lance at the windmill. Nowadays not so much. The wall and windmill always win and it eats at your soul.

  6. Wrenching late into the night, peeing in the backyard, and hopefully having a cold one nearby sound like good times. I remember when going to the bar sounded like more fun than this but probably not anymore. Getting older is a strange journey.

  7. I had a similar issue with my ’87 XJ, it would overheat under specific conditions, but not all the time and had no other indicators of internal engine issues(water in oil, combustion gas pressurizing the coolant system, etc). I eventually changed the radiator for the same reason that you did – running the heater helped quite a bit – and it never had a cooling system problem again. I sold it at 350K miles and I saw it cruising around town for at least a couple years after I sold it. I kinda wish I’d have kept it, it was a rare two-door model and in pretty good shape, but nearly every piece of plastic in the interior was bleached out and/or otherwise ruined and I could never find a two-door in a junkyard to rob parts from.

    1. I have used the “heater fixes it” radiator diagnostic test twice on Subaru’s. I own one of those pistol grip IR thermometer gizmo’s, but there’s just too much crap around a radiator any more. Can’t get a hand on it anymore either.

  8. First off, I want to say congrats! Also, did you remember to take off the headband spotlight before you got to TSA this morning? You are an absolute maniac 🙂

    A semi-serious question though:
    After its all is said and done, including the drive to Chi town (which, btw, is a maniac thing to do right after a flight from Cali. Forget trench foot, you’re gonna give yourself hemorrhoids!), how much money did you lose in total on the car?

  9. Yay, congrats! Your euphoria definitely comes through!

    Also, I believe you have just delightfully illustrated the traditional plot arc of a superb romantic comedy:

    –Meet-cute (boy meets XJ)
    –Appealing leads with quirks and idiosyncracies
    –Vexing obstacles to surmount
    –A helpful and charismatic sidekick (from Toronto)
    –Happy ending (not necessarily together, which adds evocative depth)

    Extra credit: a Chicago thematic element

  10. Hooray! I love reading stuff like this. The trouble, the thought process, the trials and errors, and ultimately the big pay off of victory!
    Plus, instead of just having a beer at a bar with David Tracy, he got to do David Tracy things with David Tracy at Chateau David Tracy! Wins all around!

  11. Filth snakes, slithering in mold-cheese and DT shitting on newspapers strewn on the floor

    Although the lady next to me didn’t say anything, I’m sure I smell of polyethylene glycol

    wrenching at the expense of my social life, relationships, etc

  12. David I sure hope you are getting some sort of sponsorship from Blackstone Labs because I had never heard of them before you mentioned them in a story and I’ve used them at every oil change of my shitboxes since! Sweet sweet numerical data…

  13. I was driving yesterday and saw a narrow boxy Cherokee raised with no rear bumper and a sticker inboard of the right taillight cluster. It was 4.0l in a red slashed circle. I laughed and realized “no amount of explanation” so I just accepted that my family knows I’m strange.

  14. David,

    Congrats on getting this heap up and running – now get it out of your fleet when you get back from Raptor bashing.

    One thing I would recommend is to WEAR GLOVES when wrenching. Even cheap disposable latex gloves can prevent grease from getting under most of your fingertips (yes you will likely rip the tips of the glove’s index finger, but usually only one or two fingertips will be destroyed in my experience). If you can figure out where to get the heavyweight gloves Ed China always seemed to have, those would be even better. If you can get over your ultimate cheapness, mechanics gloves work too. You will save enough on hand cleaner to pay for the cheap gloves.

    Also, as noted by the commentariat on your last Jeep post – next time have the machine shop do the valve job – yes it will be a few hundred dollars, but the head will come back better than you can do in your yard, and you will have time to write another story to keep this site going.

  15. Congrats DT on finishing it up….. (now as a reader of this great new site, there is a sadistic small, small part of me that wants something else to go wrong. This will then make for another great article. ????)

  16. In honor of this post, I am taking the radiator out of my Econoline to be flushed, inspected, and re-cored if necessary. The engine to that radiator is in the middle of a full rebuild do to a failed water pump, but after following this saga I’m not leaving anything to chance.

  17. Congratulations man! The relief of getting a burden out of your life like that is always great.

    These sorts of things are why I have really cut back on my project count, and instead focus on being very thorough about them. Sure, you get less variety, but you also get less headaches. A decent water pump can be yours for $30 shipped from rockauto, the Spectra radiator is the best value around and rebranded in several places is $135, and if you really want to thoroughly clean the block, the biggest cost of replacing the freeze plugs to clean out rust buildup behind them is the intake and exhaust gasket for $20. That’s biggest parts of a complete cooling system replacement and service for less than $200, not including the various other line items that add up. That preventative cost becomes well worth it when the alternative is replacing a cylinder head or worrying about a cracked block, and you ended up replacing many of those parts anyways!

    I know you say things like this would be done if it was in your regular fleet. Just keep things like this in mind for when you’re planning out the ZJ build – trying to spend less cash by assuming wear parts are good can backfire and eat into your financial and mental health. It won’t get better overseas! Go overboard with replacing cheap parts now like brake soft lines, caliper rebuilds, cooling system service, etc. and you’ll have a dependable machine.

    And then you can keep writing about reviving weird old junkers, possibly in far off countries, that you can walk away from without stranding yourself or someone else! 🙂

  18. Overheating hoopties sometimes prove difficult to diagnose. Sorry it’s long but…
    Chasing an overheat/didn’t overheat condition in an old Datsun PU.
    Followed no (obvious) pattern. No bubbles in radiator, no milk in the crankcase. Sometimes high speed, sometimes idle. Sometimes perfect cooling operation. Heater activation made no difference. Went on for months but progressively worse.
    In the process of pulling the radiator for service/replacement, pulled rad hoses to ease the job. Inspection of hose interiors revealed the return hose had delaminated internally. The hinged rubber flap formed a rather effective intermittent check valve. Especially under high flow condition. Lesson learned: rule out nothing.

  19. Way to stick with it, David! You’re my backyard wrenching hero!
    I know the wrench-for-4-hours/ponder-for-4-hours experience well.
    Last one was getting around a replacement power steering line pressure switch config that didn’t match the truck. Had to “manufacture” a connector for that one.
    For our sake, hope you never have a fleet of super-reliable vehicles you never have to work on.

  20. Can we talk about how someone created a convector, called it a radiator, and still today we call this contraption that performs its heat exchange almost exclusively through convection a radiator, even though it radiates an insignificant proportion of the heat it’s tasked with extracting?

  21. LOL at JT’s editor’s note. If I made a plan to meet up with David and it DIDN’T turn in to a wrenching session under an absolutely non-negotiable mega time crunch I would be extremely disappointed. Maybe the next time I make it to Detroit I can have the David Tracy Experience.

    1. Also, can’t wait to read about the Bronco Raptor. I want one. I just re-committed to my FJ by dumping tons of time and money and effort into it so I won’t be getting one, but I still want one.

  22. Well done! That sounds like the project from Hell. Y’know, as much as I laughed and wanted to give you shit for your comment about your house, I get it. I outsource a lot of my non-simple car repairs but am dangerously pro-DIY for home projects. And I’m always finding ways to get myself into trouble.

    These past couple months, I had my floors in my main living area ripped up and replaced with vinyl plank. I had removed all the baseboards and casement molding and once the floors were installed, I needed to buy new trim, put it back together myself and paint. Simple enough job right? Well, no, my dumb ass instead immediately leapt into replacing my privacy fence, which of course was a shitshow that took much longer than expected. Then, I’d started seeing someone at the time, and had to have her over for the first time with a house in disarray, missing trim, furniture still in odd places and a backyard littered with construction supplies. I normally pride myself on keeping things up, so I was stress cleaning until well past midnight the night before to make it *somewhat* presentable.

    Projects of any type can take over your life man, and I’ve been there plenty of times. I’d take this weekend to put everything else aside and get things back in order. You’ll feel so much better and it’ll be way easier to focus on all of the things you want to with surroundings that don’t stress you out.

    1. My pleasure! I’m just glad I could put some of my rusty knowledge to good use. 🙂

      FWIW, I was halfway leaning toward radiator but … yeah. You know why I didn’t want to tell you to just replace the radiator, besides cost. That job sucks.

      Root cause from a distance, at this point, I think I have a pretty good idea of what exactly happened here. One, you had a silent head failure going on for several thousand miles. But it wasn’t bad enough to warrant pulling it by any stretch. No milkshake, no problem(TM). When the water pump went, the system got hot, which starts dislodging all the Sluj(R) that built up in the system. Add air ingestion into the mix, and you can just imagine the frothy delight going on in your radiator. (Please don’t if you plan to eat today.)
      So all that crap got pumped into the radiator, with nowhere to go because the water pump wasn’t working at all. Which consequently clogs up the channels. But these bastard radiators are downflow. Something you probably did not learn in your time at Chrysler: downflow radiators are REALLY fucking good at hiding even significant blockages. You’ll hook up the garden hose going full blast, and get as much out the bottom as you seem to be putting in the top. Even when literally half the channels are completely plugged. (Remember, we didn’t have fancy $40 IR thermometers back then. We were lucky if we had a meat thermometer. :P)
      Because the radiator doesn’t have much margin, and has offset fans? Yeah. You know what happens there. It’s why people are completely wrong when they insist 3-row downflow units are ‘better.’ It’s always been the margin versus Coolange(TM) Sluj(R), and the Sluj(R) always wins. Because it’s a downflow. And when you have an entire side getting zero coolant with unequal fans, uh-huh. Which is exactly why you check fans first – bad fan acts like a plugged radiator, but is far less painful to fix.

    2. Congratulations on the repair. I had an old truck that had the same symptoms as your Jeep. Thankfully I didn’t have to troubleshoot it because the radiator blew a side partially off when I was revving it in my driveway! When it blew apart a ton of black crap spilled out onto the ground.

      I watch a lot of YouTube mechanics videos and one guy said a way to diagnose a clogged radiator was to use a temp gun to find cold spots on the radiator. Good tip to keep under your hat!

  23. Well done, sir. Nothing like walking into the house covered with car dirt and saying “I win.”

    Enjoy driving the new Bronco Raptor. I am sure nothing could go wrong with the engine of a brand new Bronco!

  24. Well done! I know I am not alone in having been waiting for this exciting update! Came down to the wire, but well done man! Congrats on finally getting it done. Make sure to give another update, hopefully a much less exciting one when you get it delivered. I truly hope it is like 3 lines long, drove to Chicago, nearly died due to gas prices, dropped off the Jeep from hell to the nice lady, drove/got a ride home, gas prices again caused tears. The end.

  25. The idling issue ruled this out, but I’m going to put it out there in hopes it helps someone. A little late ‘80s or early ‘90s truck would overheat every other Friday when the owner drove ~35 miles to clean a house. Would idle for 2 solid hours without issue. I took it up&down the Parkway for 3 hours, and the needle moved a >bitwhole< system and not just focus on familiar pieces

    1. Well, comment seems to have been partly redacted.
      Basically, someone neglected to reinstall the spring in lower radiator hose, and, with a partly clogged radiator, truck would overheat when sustaining over 3k rpm. Idle & drive around town for hours just fine.
      >>always look at the whole system was my lesson there

  26. Congratulations sir. you were bold to sleep after the repair, I would have driven straight to chi town and dropped it off before it could have any more issues, but that is me and I do not take well to cursed cars.

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