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XJ Overheating at High Speeds

thr0we

NAXJA Forum User
Location
United States
I have a 1994 Jeep Cherokee 4.0L with 160k miles and I've been recently having some troubles with it overheating. It will usually run just under 210 when cruising around, but if I get on the highway and have to go around 60 mph it will jump up to around 220-230 and I have to start using my heater core to cool it down. With fall right around the corner it hasn't been reaching scorching temps but it has gotten to around 240 before. I'm completely dumbfounded because I have replaced every single component in the cooling system and still have no idea as to what it could be. I've replaced all the hoses and flushed it really good two days ago as well. I have no idea what else it could be. Some are saying a new radiator might be the fix and others say it might have a blown head gasket. I just want to finally solve it and not have to worry about it anymore.
Any and all help is much appreciated, thank you!
 
I was going to suggest the water pump, but sounds like you already did that.

How did you set the tension on the serpentine belt? Does it squeak/chirp at all? Tension spec for new/used belts on these things almost seem absurdly high: 180-200 foot lbs on a new belt, 140-160 foot lbs on any belt that has been run for 15+ minutes.

I spent the couple bucks on Amazon for the necessary "Krikkit-II style" tension measuring tool (https://smile.amazon.com/gp/product/B000CRDLZM/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1), not very expensive and easy to use.
 
Overheating at high speeds is typically a water flow issue. Worn pump (or reversed pump if you got the wrong one), clogged radiator, passages ect. You can do a leak down test on the cooling system to rule out the head gasket. Most likely if the head gasket is blown you would be overheating in all operation modes.

You mention replacing every component then some saying it could be a clogged radiator. Have you replaced the radiator? Or everything else?

It's not uncommon for sediment to build up in the bottom of the radiator over the years. It gets in though the overflow bottle since that is open to atmosphere.
 
I was going to suggest the water pump, but sounds like you already did that.

How did you set the tension on the serpentine belt? Does it squeak/chirp at all? Tension spec for new/used belts on these things almost seem absurdly high: 180-200 foot lbs on a new belt, 140-160 foot lbs on any belt that has been run for 15+ minutes.

I spent the couple bucks on Amazon for the necessary "Krikkit-II style" tension measuring tool (https://smile.amazon.com/gp/product/B000CRDLZM/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1), not very expensive and easy to use.

Krikkit II should be a required tool for any XJ owner.
 
Have you done a chemical flush? Overheating at high speed is an indication of insufficient radiator cooling efficiency. Could be blocked passages in the radiator, contaminated fluid, or radiator fins packed with dirt.

I had a similar issue with mine and after replacing every part, I started back at step 1 and did a complete system flush. I used a chemical flush additive. I ran 100% distilled water with treatment. Drove ~50 miles (a couple heat cycles) and then drained. I refilled with 100% distilled water. Drove another ~50 miles, and drained again. I repeated this process until the water draining out was as clean as it went in. Then I mixed 50/50 distilled and coolant. No more overheating.
 
I have fought with crappy fan clutches. I Went through 2 new ones from Autozone. I swapped a heavy duty one from a 93 Grand Cherokee from RockAuto. It pushes a lot more air. It appears to have fixed the overheating issue.
 
While I agree with owning the Krikit II I found that with my '96 that I used to own the "yeah that looks about right" method always seemed fine.
But with my '00 she was more particular about the belt tension.
Why I bought one.
One thing I can tell you about the "yeah that looks about right" method.
It is pretty far off.
When doing the '00 I tried that method first and then check with the gauge.
I want to say I was at about 100 lbs. LOL.
 
You could just go right hand drive, we have a spring tensioner like every other car in the world, lol.

Anyway, there is a good chance you stirred up the sediment and clogged the new radiator. When i put in a used engine I took it to the car wash first without the wp or thermostat in it and alternated spraying the high pressure water in both holes and it took an absurdly long time for the water to come out clear. New everything else but a heater core and i can deliver mail in 100 heat with the ac on high all day long and it stays rock steady at 210 with stock fan, clutch, and e fan. So in my experience anyone who tells you that you need fancy cooling upgrades on a stock set up is incorrect. I believe sediment clogging up cooling passages is the #1 problem with overheating xjs, and its just so damn hard to get them completely clean.
 
I just tightened it until it felt right, it squeaks a little bit and more when it has moisture on it. Would you recommend tightening it?

Yeah, I'd say it's probably loose if it squeaks all the time.

The tool I linked is only $22 (might be able to get it cheaper at your local NAPA for all I know), but then you'd know for sure whether you've got it tight enough or not.

I got mine several months after doing a water pump in an offroad park staging area; at the time we did "until it felt right" so I could drive it, but I wanted to be sure I'd gotten it tight enough for the long-term. When I tried the Krikkit II on it, I found I was low by something like 40-50lbs of tension or more, like what Ralph77 experienced with his 00. Properly set tension per the Krikkit II really can feel like "someone broke out the air gun and ran it up to nearly snapping".

Still the sediment theory Wolverine mentioned could be a factor too - did any gunk come out in the last coolant system flush you did?
 
Stretched out timing chains can also cause an overheat condition but usually at lower engine speeds.

Sent from my SM-G892A using Tapatalk
 
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