Why is my fender overheating?!

[Number21]

I just bought a 1998 XJ with the 4.0/auto and 184,000 miles. Seems to be very well kept, runs great, everything seems to check out OK. Then I drove it about 150 miles down the freeway with the A/C on, and it died. As best I can tell the box with the relays in it on the passenger side fender is overheating, killing the fuel pump and the engine. It starts and runs fine again once it cools off.

I can't figure out why this is getting so hot. It seems like hot air is blowing out of the small square hole in the fender behind the battery. If I just let it idle for about 10 minutes with the hood shut, the outside of the fender heats up to over 170 degrees according to an IR thermometer! The box with the relays is almost as hot. If I leave the hood open it doesn't get as hot.

My coolant temp never gets above 210, usually lower. Does anybody have any idea why hot air would be blowing out of this area? It appears to have the stock fan shroud and everything else in tact. The electric fan comes on and off as it should with coolant temp and when I turn the A/C on.

I've had several other XJs in the past, many with overheating issues, but I've never seen a problem like this...

 

[cnugent]

I can't speak to the heat issue, necessarily, but I do know I had an issue with the terminals on the back (bottom) side of the relay box backing out and making intermittent connections. In my case it was most often the fan relay. It'd fail and the vehicle would overheat. Always after a time driving, so it was good and hot. Never did it cold. I wonder if the heat cycling is normal, and it's causing those terminals to open the circuit just enough to cause the failure?

Unfortunately I don't remember what I did to fix it. I'll have to go look real quick.

edit--Ok, once you remove the cover, you'll see locking tabs on the sides of the box. This unlocks it and it basically separates into two parts. If I remember, I took this apart and cleaned and adjusted the terminals inside so they'd make better contact.

--Chris

 

[Number21]

I tried swapping the relays for the fuel pump and starter when it died, and I got it to stumble and fart a little bit, but that was it. I notice the starter never stopped cranking, but I couldn't hear the fuel pump priming like it should.

I tried idling it in the shade again, the passenger fender is too hot to put my hand on, up to 175 in some areas. The other side is much cooler. Should the fender be getting that hot?

I'm not sure why hot air is in between the inner and outer fender in the first place? Am I missing something somewhere? Seems like if it gets much hotter it's going to start removing the paint...

 

[Tim_MN]

You are focusing on the wrong symptom. I would suggest that all XJ Cherokees run hot, and if the temperature gauge shows about 195* to 215* your XJ is normal.

You should be looking at the parts or systems that are malfunctioning under normal heat conditions.

The Crankshaft Position Sensor ( CPS ) is the most common and most logical thing to suspect with the symptoms described. The next time this happens, carefully look at the dashboard gauges. If you find that the fuel gauge and/or the voltage gauge are not working or are definitely not displaying in the same manner as before a cool engine start-up, you should suspect the CPS is cause of the stalling/not starting symptoms.

 

[RCP Phx]

Electrical parts produce heat when you have bad connections, I would recommend(and do use on all mine) some "Nolox" or similar on everything. It's water resistance and low conductivity is it's job. The only other thing that produces "heat" in a system would be "overload"!

 

[Number21]

I think you guys are missing the point. The underhood fuse box is overheating because hot air is being blown directly on it from the radiator. This is not an electrical overheating problem, and it is definitely not a CPS problem.

For some reason hot air is being thrown at the fusebox and fender that shouldn't be. But why??

Anybody else have a fender that is too hot to touch? I'm pretty sure that is not supposed to happen.

 

[Number21]

See the square hole in the fender behind the battery? Is it supposed to be blasting hot air all over the fuse box and battery? How did hot air get in there in the first place?

 

[Tim_MN]

You are focusing on the wrong thing, the heat is normal. Find the electrical component or OBD-II engine sensor that is weak/failing.

If you think the square hole is the problem, put some duct tape over it and see if that helps.

 

[Number21]

Again, it's NOT a sensor problem. Does your fender reach 175 degrees at idle? I seriously doubt it. The electrical components in the fuse box are failing because the air around it is overheating. The plastic cover to the box is also around 170 degrees. If any exterior body panels of your Jeep get so hot you can't touch them on a cool day, it's not a sensor problem!

NO, duct tape is not an answer. Hot air is being forced out of that hole, not in...it should not be in the fender at all. Duct tape would turn into a melted plastic mess. The question is why is it coming out there in the first place?

 

[Dragonlich1961]

Body panels will get hot, number one panel is the hood. You could practically boil water, defenently burn your hands trying to open it. Jeep xj's have a defenently have under hood temps problems. Look it up number one sensors that have notorious heat problems are the crank sensor and the cam sensor. Again the Jeep Xj has major heat problems. Numerous people spend ridiculous money trying to keep them cool.

 

[Number21]

I realize XJs get hot, I have had 5 of them. That said, they should not get so hot that the outside of the body burns you after 10 minutes from cold at idle. I'm pretty sure the fenders are not painted with high temperature paint. Usually the "running hot" problem manifests itself as high coolant temperatures, which I do not have.

I already know why the engine dies - the fuel pump relay gets too hot, stops working, and the fuel pump stops pumping. The question is why is it getting so hot? No, it is not normal to see 170+ on the outside of the fender or in the fuse box. Those components are not designed for those temperatures. Even if it ran that will cook my battery. I'm pretty sure it is not normal to see hot air blasting from between the inner and outer fender.

Clearly, it's a problem when ~200 degree air blows at high volume over the battery and fuse box. That is not supposed to happen. It's bad for both components. And it's not how they are designed to work. It's not how my previous four XJs ran with the same drivetrain. I've had CPS problems before, it was nothing like this.

 

[Demonoid369]

Well if you want to figure out if it's actually the relay getting hot, carry one in the jeep where it's cool, next time it dies, swap it out for the cooler one. If it won't start. Then the hot air isn't the problem. If it starts then you know the real answer without guessing as right now you're just guessing.
Regardless you don't seem to want to listen so do what you want

 

[Number21]

Regardless you don't seem to want to listen so do what you want

I clearly said the fuel pump was not running, repeatedly, so who is the one not listening? The CPS, and every other sensor, DO NOT prevent the fuel pump from running/priming as it should. They prevent the engine from sparking. I do not have any spark problem.

I never asked why it died, I asked why this part is getting too hot. Just because I don't have a bunch of posts here doesn't mean I'm an idiot, it's pretty easy to tell when the fuel pump isn't running. I'm not guessing, I know that for a fact. I could hear the fuel pump not priming as it should, as I have already explained. Additionally, I'm pretty certain the fender should not ever reach 170+ degrees at idle from a cold start after 10 minutes, clearly, this is not a sensor problem.

 

[Demonoid369]

Clearly you're not going to listen or reason with anyone. Here's a thought: I don't ever hear my fuel pump prime, still primes. Still runs fine.
And yes both my fenders and hood have been hot enough to cook an egg. And this is in Oregon and in the winter...
But go ahead and askhole

 

[Demonoid369]

Quick and easy fix, silicone a piece of metal plate over square hole.
Done

 

[Number21]

Clearly you're not going to listen or reason with anyone. Here's a thought: I don't ever hear my fuel pump prime, still primes. Still runs fine.

I'm not going to listen to anyone who insists there is a sensor problem without any reason to believe so and plenty of evidence to believe otherwise, especially when that person has never seen my vehicle. It is very normal to hear the fuel pump on an XJ prime when you turn the key to the run position. When it is cold I hear the fuel pump priming as usual, that is to be expected on an XJ. Once again I'm not asking if the fuel pump stopped pumping, I'm stating I know it has to help diagnose the problem.

Quick and easy fix, silicone a piece of metal plate over square hole.
Done

Sorry, I'm not looking for hack jobs and that does not solve the root of the problem. Hot air should not be forced out of this hole, something else is wrong.

And yes both my fenders and hood have been hot enough to cook an egg.

After 10 minutes from a cold idle? Additionally, the driver side fender does not get hot, this is further proof that something is wrong. Somehow I doubt you've ever actually pointed an IR thermometer at your fenders or tried to cook an egg on them.

 

[techno1154]

Every XJ I have seen have that square hole next to the battery. I have yet to hear of one that causes the relays to malfunction.

It is obvious that your XJ is special even unique in the XJ world (I am guessing ). Because of its uniqueness, no one here is able to help you.

Hey! I am on to something here :idea: . Pull the fender off and look for hidden objects such as an additional heat source or hot air duct and let us know what you did to prevent that problem from reoccurring . I know your finding will help many of fellow XJ owners.

 

[Tim_MN]

I'm not going to listen to anyone .......

Obviously.

Good luck solving the problem.

 

[Alaskan89XJ]

I confess; It's 0345 hrs., Alaska Time, rain showers, and I am in an electronic wifi dead-zone, limited to 40kbs dial-up, I cannot always 'see' what ever images members, and quests offer up to us all. Since I see no photograph/image, I reject the notion of walking outside some hundred feet due to some very big brown bears, and some little'r black bears in and around my hut, (they are actively fishing in my back yard under nearly cloud blocked moonlight), in order to pop the hood on my XJ to take a look-see, (with my LED flashlight), for a little square hole that I do not recall to begin with.., at trying to figure out the problem.., i.e., of hot air being passed through there enough to overheat that side's fender, and associated placement of the relay box.

The above declaration(s) aside, I wonder if "techno1154" might have illuminated some flashing light bulb on the subject when he referenced his brain cell figuring that maybe there is an unique 'duct' of sort, i.e., a modification. Is it possible that the P.O. had a duct, hose, or some such introduced from some water splice, or air hot air duct in order to provide extra heat towards the battery/fender in order to keep it warmer in the winter? Maybe the PO put some 12v electrical "heat-tape" down under there somewhere!?!

I think cooler heads should continue to prevail, especially since it's not April Fools. I am interested as to what in the world is going on with this person's XJ's little square hole, even though there have been some interesting diagnosis advised by greater minds,:worship: (than I), from the XJ world of issue solutions. I also find a bit of confusion going around in the general post.

Me.., Am listening to some classical music on BBC, :listenmus(Royal Albert Hall).., so I'm going to reach for an imported bottle of Irish "Guinness Stout", and a bag of imported American organic 'cheesy-poos', (last snack),thusly retiring, and calling it a night. (btw; most products here in Alaska are imported, lol, especially XJ parts.., sheesh...). Hell.., if that little square hole bugs me enough preventing me to catch my zzzzz's.., perhaps I'll grab my shotgun, and go out, and pop the hood.., damn-it...

("ummm.., cheesy-poos"--quote from Cartman).

Just my 1.5 cents.

 

[voudoux]

It sounds like an quite unusual problem,if you think about it the only sources of heat of that temperature are the exhaust(wrong side of jeep),transmission cooler(should be inside radiator) and radiator.A to this what blows air,fan,so I know this sounds odd but have you checked the fans ? some electric fans can be wired wrong and run backwards also I think the xj uses a reverse rotation fan,could be wrong fan. Just something to check,good luck (or it could be demon possessed)