Jeep Cherokee: Heat Soak & Vapor Lock Explained (Cylinder 3 Misfire, Rough Warm Start) ['00-'01 XJ]

On 50-State equipped 2000 and 2001 Jeep Cherokees, Heat Soak is a somewhat prevalent issue especially in warmer climates. If your engine runs rough on warm starts, you have a random cylinder 3 misfire code, or it fails to even stay running after recently being shut down, here are a handful of methods to fix the problem.

I used 12G wire for the fan, and 18G wire for the toggle circuit.

The 2000+ XJs can run on E-15 fuel, but they don't really like it.
They very much prefer unleaded 87 with NO ETHANOL, but I rarely find stations that sell it.

FACTORY EXISTING FAN CIRCUIT INFORMATION:
F141 12LG/RD - FUSED B(+) (Fuse 5) - Constant Power
F20 18WT (2) - FUSED IGNITION SWITCH OUTPUT - Trigger (Ignition ON)
C27 18DB/PK - RADIATOR FAN RELAY CONTROL - Trigger (ECM Ground)
C25 12LB - RADIATOR FAN RELAY OUTPUT - Power to Fan

Up Next: Operation Taco

[idleprechaun]

Hey man! Just swinging by to thank you for all your tips in previous vids. Girlfriend and I drove from the Chicagoland area to LA. We are currently headed back but got a busted TPS mid way through the mountains of CO. You mentioned in previous vids to always carry spare sensors and thank god I did. 10 minute repair in a Taco Bell parking lot and we’re back on the road. If you’re ever in the area I owe you one

[tomkatinokla]

Very good video! Years ago I installed the factory shields (which had little effect), then discovered the kit sold on Summit, which I installed over the factory parts. Helped slightly. Then installed hood vents, that helped a bit more. Use of pure gasoline vs E-10 was biggest help, though I sometimes still have issues, presumably due to inconsistent fuels. I've thought about modifying the electric fan, but have never gotten around to it. Your success with it has inspired me to get to it. Thanks.

[dhatsuyuki]

This is actually why I 2.5L swapped my XJ

[Trevosamo]

Great video, lots of good info here! My 2001 developed heat soak AFTER installing a banks torque tube header and new CARB walker pre cats. No idea why that seemed to make it hotter than the cheapo ebay header and old cats. I even started stumbling while parked and idling for long amounts of time (damn popeyes drive thru!!) But I eventually wrapped the fuel supply line and did the fan switch which "cured" it. I get a lot of concerned comments from friends and passerby's when I park and have the loud ass fan on but at least it works!

[drgil]

Thanks for your video, I’m in Arizona the weather here gets into the 3 digits plus. I honestly have to say I have never had a heat soak issue, but then I do have a 99 XJ.

[rachelfrew]

I love your videos and look forward to anything new regarding Jeep XJs. You’re amazing, please keep them coming. Nice job

[the-pezinator]

That fuel chart is so real, I can only attest for two of them but I have noticed when I get the Valero I have more instances of bad heat soak as compared to Sunoco, Sunoco I barely have issues, when I do have you soak I just push the pedal a couple of times to force more new fuel into the fuel rail and that seems to fix the problem faster, also great finally seeing this mod in "person" technically, I always have trouble comprehending diagrams and implementing them to the actual thing, being able to see both really helps me and I might actually do this mod.

[gearsnstuff]

Fun fact, a lot of old tractors have reverse flow engines, to the point that some of them have the intake and exhaust manifold cast as one unit. I have a 1923 Mack truck that has coolant plumbed through a jacket inside the intake manifold, for the express purpose of (as stated in literature for the truck) preheating the fuel-air mixture for 'Maximum efficiency'. Now, this was in part due to lower quality fuels in 1923, but that still makes me chuckle every time I think of it.

[seiser]

I solved mine with aluminum HVAC tape around the fuel rail. I really like that fan idea.

[hanaguz]

Interesting video, I have a 1994 Jeep XJ Sport and so far I have not had any problems with overheating, after putting the electric fans directly to the battery with a relay And it turns on with the key, while with the aw4 transmission I have not had temperature problems either.

[motownXJdad]

i did that D&E Bueller relay set up on a 2000 4 door i had, Doug and Eric are cool dudes. it worked great. the 2000 XJs also have a ECU problem with turning the Efan on when the AC is turned on like its supposed to, they dont do it at all, lol supposedly the dealer can fix it though, theres a TSB on it. i used my rear wiper switch on mine to be able to turn the Fan on, ive never used a rear wiper on any vehicle ive ever owned.

[anthonypereira]

I’ve got the e fan switch and heat shielding on my 2000. It wasn’t until I wrapped the fuel line in the heat shielding also that my heat soak completely went away. That fuel line runs right next to the exhaust manifold, so all the fuel in there would turn to vapors very quickly.

[kjohns]

Thanks for the help! Always enjoy the videos 👊🏽

[kylemandt]

Great video. Thanks for the details. This is awesome.

[FIRE-OWL.]

I heard the hood spacers don't really do much, I drove my 00 cherokee to mexicali for a week, so hot dessert air plus allready hot engine air, the electric fan with a switch, is def the best thing for it.

[gradn]

Ditch the pre-cats, buy the walker federal emissions downpipe, weld in two bungs post big cat, then extend the two downstream o2 wires.

[Wrencher_I]

Great video !!!! I have a 2000 xj I had to do the switch thing as well, wired it different but hay if it works it works !!!!

[hannahvaipulu]

Keep up the great content! Can you get the high idle switch to work on a manual swapped XJ?

[ProjectXJ]

I have a 97 with a new radiator and heater core. Driving down the road it never gets heat soak but when i stop or when i offroad, its been really bad. I tried the heat sheild and it helped some but not much. I got the fan override switch and hood vents that i need to install. I am hoping this will solve the issue.

[firesorcererfs]

I’ve personally never had this issue at all or even overheating i always hear a lot about overheating on this engine but I have it on 4.5lift on 33x12.5R15 with auto trans and I do drive it heard especially on the expressway and never had overheating issues