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overheating...

sooo, it overheating again :-(

hooked up the jet ski trailer to go to the lake (not much weight, its a stand-up ski) and about halfway through the hour trip the temp started creeping up and then pegged hot again. this was going about 60mph, which is odd, because it used to get hot only when idling. when i pull over to let it cool we waited about 5-10 minutes then got back on the road. it did this about 3 times. I have no idea what is wrong now after changing out nearly the entire cooling system :-/ I'm really confused as to what it could be now
 
space_monkey said:
sooo, it overheating again :-(

hooked up the jet ski trailer to go to the lake (not much weight, its a stand-up ski) and about halfway through the hour trip the temp started creeping up and then pegged hot again. this was going about 60mph, which is odd, because it used to get hot only when idling. when i pull over to let it cool we waited about 5-10 minutes then got back on the road. it did this about 3 times. I have no idea what is wrong now after changing out nearly the entire cooling system :-/ I'm really confused as to what it could be now
Click to expand...

I would take a closer look at the 0331 Head, They do not like to get hot!
 
I have an overheating issue also in my 91. Replaced literally everything in the cooling system, even installed an aftermarket all aluminum radiator. Will idle fine,drive on flat ground fine, but cannot go up grades or hills, or pulling a load without it overheating. Did a head gasket and had the head checked for cracks, found none. Not sure what to do now. Another machine shop said it sounds like a cracked head/block, but no milkshake in the pan. It even runs strong enough to smoke the 31/10.50's thats what doesnt make sense.I have the 720? head also. I'm putting my money on a cracked head that the last shop missed.
 
cherokeefan_1 said:
I have an overheating issue also in my 91. Replaced literally everything in the cooling system, even installed an aftermarket all aluminum radiator. Will idle fine,drive on flat ground fine, but cannot go up grades or hills, or pulling a load without it overheating. Did a head gasket and had the head checked for cracks, found none. Not sure what to do now. Another machine shop said it sounds like a cracked head/block, but no milkshake in the pan. It even runs strong enough to smoke the 31/10.50's thats what doesnt make sense.I have the 720? head also. I'm putting my money on a cracked head that the last shop missed.
Click to expand...

Plumb in an external tranny cooler if it is an automatic. Going up hills and towing, if you are shifting a lot you are cooking the tranny fluid. This helps heat the coolant up with the interchanger in the radiator. By plumbing it externally you can separate that out.
 
Yeah, its an automatic trans. I had been considering an external cooler since i ripped out the floor. The heat from the front floorboards near the transmission is intense, and looking around i'd rather find a cooling solution that bypasses the radiator, rather than inline with the radiator. If anybody has any suggestions for that it would be great.

Thing that gets me though is that we're talking about a single stand-up jetski on a small kit trailer. Not heavy at all..

Weird, but I will do some more testing to see if I can find any other telling symptoms.
 
I have replaced all cooling components similar as Cherokeefan_1 did but did not done the head gasket (7120) since I dont think the head is cracked. Compression between 150-160 all 6 cynlinders. Also added transmission cooler.
In my case ambient 100 F + AC+ uphill long grade = overheat.
Ambient 100 F + uphill long grade = okay
AC + flat freeway = okay
AC + uphill long grade = overheat.
I am not pulling the trailer but my XJ is heavy due to rear cargo storage roof rack, front, rear built bumper and rock sliders. For now I am just take it easy on the summer heat and I think it will be okay during the winter.
 
Still overheating today, going about 35 mph after about 20 mins of stop and go traffic and the temp shoots up. As im pulling into a parking lot it went back down like 230 or so even withstood a little more stop and go traffic, weird. I popped the hood and verified that the aux fan was running when I got home.

We have been having record temps here in Texas, so I'm sure that isn't helping either. I guess aux transmission cooler + new radiator is next.



:smsoap::flame:
 
well i have some heat problems but nothing over 220 yet... but i can idle in a parking lot with the ac on and it cools down but get out on the highway doing 40mph or higher and it starts to heat up again. so i bought a tranny cooler and a temp guage and i will put in my old 3 core radiator and see how she runs if still hot then i will pull my water pump and check it out.
 
I forgot to mention that I have the biggest hayden tranny cooler that would fit installed in my 91 and not going through the radiator and overheats still. Especially up hills, doesnt even have to be that long of a hill. Using the a/c helps on short hills but not any type of longer grade.Used a 16lbs cap over the 13lbs I used to have with no change. I really dont want to dump a case or two of 7.62x39 into this thing but am getting close to doing it.:D
 
Haha I know that's ammunition I own lots of guns, that's just the last thing I would of thought of (a guy shooting his jeep) haha. But if u are going to shoot it do is right and use a 44 or 30-06 :D
 
Temps are starting to look stable now. What I did since my last post was get one of those prestone "flush-n-fill" kits that hooks up to the heater hose. I highly recommend it. Lotta brown fluid came out and it hasnt overheated since. My plan now is to pull the thermo and flush again, so i can get it ALL out, then do one of those extended flushes (drive for 500 miles then drain). It's been pretty stable now even sitting in traffic and on the highway, but I'm still scared to hook up the trailer to it, lol. I will try that after the full flush is complete.

I thought I could have been dealing with a lower hose collapsing issue because the new lower hose doesnt have the metal spring in it. Most forum posts seem split 50/50 on whether or not having that spring is an issue. If I still overheat I'll probably order a cool-flex since its about as much as a dealer hose anyway, and cheap insurance. Also, I cant find replacement heater hoses anywhere that are molded correctly, but they aren't too bad from the dealer (like $40 for both).
 
Sounds like you had some air in the cooling system. It' a very common issue after draining and filling the system. Looks like you "flush-n-fill" kit fixed it. You should be OK now.
 
'91+ 4.0Ls are self "burping" and it is not common to have air in the system after filling. You should watch the reservoir through a couple of hot/cold cycles to refill as needed.

It is common to have problems with air in the system in pre-'91 4.0L closed systems.
 
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