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:
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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?
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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.
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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.
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.
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.
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[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.
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.
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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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!
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.
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.
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?
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.
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.
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! 🙂
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.
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.
Nice work, David.
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. ????)
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.
HUZZAH!!!
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.
I laughed, I cried, it became a part of me. Cherokee From Hell. Now and forever. I’m sorry, there’s something in my eye.
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…
Congratulations! I’m relieved to hear you got it solved, but not as relieved as you. 🙂
I’m glad you figured it out. I know how it feels to get burned out working on a project vehicle.
You keep saying “nice lady,” but instead of pulling over she drove a vehicle that was overheating further until it broke the head. She’s a _murderer_!
*Attempted. He was able to resuscitate the Jeep, so she tried but failed.
Jeremy, you did the community proud that night. How many people would gladly accept meeting someone for drinks getting changed to replacing a radiator and pissing in the yard?
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
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
Damn it. I said RADIATOR David…Where is my prize? Sometimes it’s the just the simplest thing, but is often overlooked because of brain farts?
Way to bury the lede there. What’s the over/under on David blowing a piston in a Bronco this weekend? ????
Is the 3.0 V6 in the Raptor related to the standard 2.7 V6? If so, then it’s like 10-to-9 odds.