Summer temps - XJ Starting to run hot.

Yesterday it got up to 89 degrees here in Houston.

I left work about 2pm and on the way home I was driving between 75 and 85 mph.

After running down I-10 for a few minutes at 80+ I looked down to see the temp guage approaching the 220+ mark.

I don't drive down much of I-10 before I exit (especially at 80 mph) so about the time I was exiting I turned off the A/C and rolled down the windows.

After about 5 minutes it was just a hair above the normal temp of 210.

Now everything I know it should run cooler at 80 mph and hotter at 20 mph, especially in stop and go traffic. That wasn't what I was seeing.

I have plans to get a better radiator and an electric fan to replace the mechanical fan, but before I do I want to get your opinions.

Seems to me that maybe what is happening is the belt is slipping under high rpm, with the A/C on. Perhaps the A/C compressor is having an issue and is harder to turn.

I have had problem with the belt slipping on the tensioner pulley in the past. Maybe I need to replace that shinny wheel.

I am thinking that is belt is slipping causing the fan to turn slower, and perhaps the water pump, that putting an electric fan might help.

Oh, of course the obvious thing to do is tighten the belt, but I had a water pump bearing go out because I had it to tight in the past. Had to have a tow truck take it home it was so wobbly. I'd rather spend that $110 towing fee on more Jeep parts.

Check your mechanical fan clutch too and make sure it's up to par.

General rule of thumb

Running hot at highway speed = radiator or impeded circulation (water pump, blockage etc.)

Running hot at idle, in traffic or wheeling at low speeds = fan, fan clutch, electric aux fan not operating correctly.

I doubt that a "sometimes" loose belt would cause you to get that hot on the freeway.

Check your radiator, coolant leve, coolant condition, oil condition.

I have had this happen on another vehicle. I would check to see if your lower radiator hose is collapsing at higher RPMs. Chances are if you replaced the lower hose without transfering the spring, this could be your problem. Good luck!

Sideshow said:

I have had this happen on another vehicle. I would check to see if your lower radiator hose is collapsing at higher RPMs. Chances are if you replaced the lower hose without transfering the spring, this could be your problem. Good luck!

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This was the first hose I had to replace. It's been several years now. I remember the spring, and I remember putting it in the new one. Maybe it is a good idea to repalce that hose again. I can check the spring location too.

Thanks, good information.

Mine always runs at 220, no matter what the temp outside. Is that OK, or should I change the thermostat? It will climb up there, then the thermostat will open and you can see it drop 10 degrees or so, it's just always done it. :dunno:

When everything is warmed up and the rubber is pliable, rev the motor and look at the lower rad hose. Not sure but this should give you enough vacume to see if the hose is colapsing.

Steve_Moore said:

Mine always runs at 220, no matter what the temp outside. Is that OK, or should I change the thermostat? It will climb up there, then the thermostat will open and you can see it drop 10 degrees or so, it's just always done it. :dunno:

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I dunno. Mine has been 210, a hair below, since the day we bought it new. It is a 1998 XJ Classic.

I've been fighting the engine cooling system since 2001! lol

220 ant that bad on a old stock gauge but.
Clean rad out very well, Mud in the fins can hide behind the condenser and grill.
Top off rad if needed
Is it running well in general?
Are you losing coolant?
Are there any sounds, smells etc that would make you think it's over heating?
If no. The temp gauge maybe a bit off have someone with a gun check off the T housing.
AT 220 your not bad but my crystal ball say clogged rad. If so. Don't home flush. It's to late. maybe pull and have it boiled out. But if the rads more then 5 years old (IMO) Don't flush at all. Save your coin and get a new one.

Check air flow into engine. A/C condenser , rad plugged (bugs,mud,etc). Also check under hood temp. I had the same problem with new motor, trans, drive train, everything! Temp would be 215-220 at highway speeds,190 on streets. It would climb to 230-240 under load (climbing a grade). I cut the hood, put on a louvred hood grill and the temp dropped back to normal, 190-210.

Newer hoses don't come with the spring. The hose that was on my Jeep when I got it didn't have the spring, and the Delco hose I replaced it with doesn't have the spring.

Never had any problems with the hose collapsing. The newer construction of the hoses does not require a spring.

Ok I drove home today and didn't exceed 72 mph. Temp was better. When I got home I grabbed the IR gun and started getting some temps.

Just for grins the hood was 175 degrees, as was the inside of the hood.

The thermostat case was 210.5



The Jeep temp gauge read over 210 degrees.



The over flow bottle level was just below the FULL line.

Yesterday the needle was much closer to that first hash mark after the 210.

The outside air temp today is 91 degrees, so it is hotter outside than this time yesterday.

UPDATE: Ok well screw it! I just ordered a 3 row radiator from radiatorbarn.com (gotta love that name).



I called them and asked them about the size of the tubes. They are the same size as the two row (core), just one more row. Helpful, professional, now I'll have to wait and see how the rest goes.

Don't forget that the temp sensor on pre 97 XJ's is at the back of the head. So the temperature back there will be cooler than that of the thermostat.

And the coolant inside will be hotter than the exterior of the thermostat housing. Shouldn't be by much though.

Blaine B. said:

Don't forget that the temp sensor on pre 97 XJ's is at the back of the head. So the temperature back there will be cooler than that of the thermostat.

And the coolant inside will be hotter than the exterior of the thermostat housing. Shouldn't be by much though.

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Mine is a 1998.

Good I was afraid my sensor, or gauge was wrong.

dang same problem here... aux fan kicks on.. and its cracked so it vibes like a hoe

Does the aux fan come on with the compressor? Mine got unplegged somehow and it overheated with a/c but not w/o so I traced it down and found the aux fan unplugged. So check yours.

A/C really shouldn't make a motor overheat. It's putting a small drag on the motor is all.

Dave41079 said:

Check your mechanical fan clutch too and make sure it's up to par.

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Thanks, replaced it about a year ago. I didn't notice any change.

90Blue_XJ said:

Does the aux fan come on with the compressor? Mine got unplegged somehow and it overheated with a/c but not w/o so I traced it down and found the aux fan unplugged. So check yours.

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Yes it does. I have forgotten to hook it up after working on the belt etc... It is really easy to hear, so I notice it especially since I am hyper sensitive about my engine temp.

Blaine B. said:

A/C really shouldn't make a motor overheat. It's putting a small drag on the motor is all.

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I agree, but I'm just trying to figure this thing out.

I know "the hard way" that once the temp gets a little over 220 the engine will quickly go from hot to over heated, at least on the gauge.