So I recently bought a pretty well built XJ. Some of the few, more important mods I think might have something to do with it heating up are the following. HP D30 front, ford 8.8 rear. Both locked. 4.56, running 35s. It has 2 fans up front. Both seem to be working fine. We replaced the water pump and most of the important hoses, thermostat and other minor parts. It's still heating up ON THE HIGHWAY ONLY! It seems like the faster I go the more it heats up. Was thinking of replacing the radiator next, but I have a strong feeling that's not the culprit. Plus it looks pretty good, no leaks or damage to it. 96 XJ 4.0 inline 6 engine, aw4 automatic transmission. Please help!

 

It would help if you told us what year, motor and trans you have

 

Wrote the post in a hurry. 96 XJ 4.0 inline 6, automatic aw4 tranny.

 

So I take it you aren't here to help, just to be a smart *****?

 

Actually no, that's not what he was doing. That was a pretty standard first question on this board because any of us who would like to help you need to know what machine we're working with. Any time you post, you should include that info so people give you the correct response.

 

You're right, guess I just expected some pointers or advice from him.

 

these two fans, are they the factory clutch fan/electric fan or are they double aftermarket type fans?

if factory, i would check or replace the fan clutch. and again, if the electric fan is factory, is it coming on when it gets hot?

do you have a proper shroud in place?

if they are aftermarket, what side of the rad are they on and are they a push or pull type, and are they the correct (push/pull) for what side they are on?

but there are many parts to your cooling system that needs to be working properly.

 

Take off the grill. What does the front of the radiator look like? Caked with a bunch of mud or can you see through easily. Did you replace the lower radiator hose by chance?

 

Just spitballing some ideas:

I think I would consider a cooling system overhaul. If this Jeep is new to you, you really don't know what condition the cooling system is in. So radiator, cap, thermostat, hoses, water pump and fan clutch (if it still has the mechanical fan) and flush flush flush. I hate to just throw parts at a problem, but a cooling system overhaul is really just regular maintenance on an XJ.

Also, this might seem like a weird direction to go, but how's the transmission? An overheating automatic transmission can dump heat into the cooling system. Maybe you're asking too much of a tired AW4 with that big axle and fat tires.

A blown head gasket can also cause overheating on the highway, but I wouldn't jump directly to the worst conclusion.

 

The left fan is stock clutch fan, right fan is electric fan. The electric fan has its own switch in cab with three settings (always on, on with ignition on, and off). The fans are good and working properly, those aren't the problem.

 

I think you brought up some great points, some of which I have thought about. I have heard of the tranny dumping heat into the cooling system and heating it up, unfortunately that is the direction I'm leaning towards... The PO towed it around so it didn't matter what the tranny did at highway speeds, he only crawled it off road. Now I'm trying to make it my DD and I don't see that happening. If it was the tranny dumping heat into the cooling system, what would be my best option to fix it? Just replacing the whole transmission? To answer your question, the tranny seems fine to me. It does however, rev up to 3600-3800 rpms for about 3 or 4 seconds then drops back down to around 2200 when accelerating on the highway.

 

Radiator seems fine externally, and yes I replaced the lower radiator hose.

 

By the way, thank you all. Y'all have all thrown out excellent points.

 

Wait, what?

Am I your personal internet assistant? Should I be waiting at my computer, just waiting for you to log on?

The question asked was legit. And thank you, extrashaky, for explaining why I asked the question. Also for your advice, it is exactly what I would have told him.

OP, if you want advice...you need to learn to be patient sometimes. If I don't reply right away, someone on here will. I have my own junk to work on. That said, if you want to take some of the load off your cooling system, get an auxiliary cooler for the trans. Replace the rad at the same time. Just because it "looks okay" doesn't mean it is. Maybe it's got some sediment or scale in it, preventing it from doing it's job. It's also inexpensive.

 

You put a spring in the lower hose or swapped the spring from the old hose into the new one?