CMI86

Let me start off by saying hello. This is my 2nd XJ. First was a lifted toy this one is MN winter transportation for the fiance and new baby.

The issue is that after reaching operating temp the needle slowly creeps up past 210 and continues climbing to the last white line before the red on the gauge. This will happen faster if I am heavy in the throttle or jumping on the highway. I have noticed the AUX fan never kicks on so I jumpered it to see if that would lower temps, it did but not by enough to think the lack of AUX fan was causing an issue.

I work as a lube tech and had the mechanic look at it. He confidently ruled out a head gasket issue and said the coolant looked good too. He gave me a lot of maybe's that really only involve throwing parts at it until the problem goes away.

Are there more common XJ issues that would be good places to start looking for a problem like this ?

Thank you.

beasticles

When I bought my XJ I had to replace a fuse to get my aux fan working again (the aux fan relay was actually fine). Search my posts if you want I actually posted pictures and detail. The symptoms you are describing sound like either aux fan is not operating as it should, or your thermostat is going. Could be other things as well.

beasticles

I meant to add that the symptoms you are describing are similar to what I was experiencing with the inop aux fan.

CMI86

Thanks for the reply. I thought that too and noticed my aux was not kicking on due to a bad relay. Temporarily bridged the relay with a razor blade to force the fan on at all times. It was enough to keep it a smudge over 210 under normal driving but as soon as I started hitting the gas harder the temp went up to a little under the last white line.

Pelican

Do you have any idea of the history and what maintenance has been done on the system?

Throwing parts at a problem is generally not the best way to go at it but the entire XJ cooling system can be replaced for something over $200 and sometimes the best way to go at it on an old system is to just replace the whole thing while you are in there unless you are certain some components have been recently replaced.

Just a thought.

CMI86

No idea on maintenance history. We bought it from a used dealer a week ago. On the half hour test drive all was well. Hit the freeway for about 10 minutes on the way home and the temp ran up. Now it runs up slowly in normal conditions and quickly at high speed or under load. The truck does have 283k on it but judging by the miles it has and that it still runs, the condition of the truck and lastly the quality of replaced components. I would wager a bet the previous owner took fairly good care of it, but then again I have no proof.

Also I forgot to mention the heater core was deleted from the system by the sales lot because it was leaking. Could the reduced capacity of the cooling system have anything to do with the overheating ??

Pelican

Reduced capacity of the heater core shouldn't have an impact. As you probably know, turning on the heater can reduce operating temps a bit but that is just a bandaid.

Are you saying that it idles okay temp wise?

You could easily replace the thermostat (195* Stant Superstat or OEM preferred) to get started. A vague idea of the condition of the mechanical fan clutch can sometimes be determined by spinning it while hot and cold.. If you know someone with an IR thermometer, you can confirm system temps.

tjwalker

Deleting heater core should not be in play for your overheating. But with you in MN, are you willing to drive this XJ in the winter without heat? I'd SERIOUSLY reconsider this before the cold sets in. If you don't have good heat, this is a 3 season vehicle, period. I live in central MN and I remember more than a handful of days where the thermometer read -28 farenheit. Those days are not that far ahead.

I agree that a total overhaul of the cooling system is the best bet. Including a new heater core. Parts are cheap. You do the work. Put it up on the hoist at your work and have at it!

*Radiator
*Water pump
*Thermostat (195 degree, I recommend a MOPAR stat)
*Heater core (this is the repair that is the most involved; do your homework before digging in)
*Clutch fan
*50/50 mix of conventional (green) coolant. Either premixed or mixed by you with distilled water
*Radiator cap

beasticles

Replace the fan clutch. The symptoms of overheating at highway speeds is a telltale sign of a bad fan clutch.

tjwalker

Normally, overheating at highway speeds is related to the water pump or radiator.

Overheating at idle is more telltale of a clutch fan.

djb383

Negative........if the cooling system is functioning correctly (water pump, stat, radiator), no fans at all r needed at hi-way speeds. At hi-way speeds there's more air flowing thru the rad than any 11" fan(s) can possibly pull thru the rad. Throwing money at the XJ cooling system can never be considered as money wasted.

beasticles

Yeah sorry I had it backwards! Don't listen to beast

djb383

I would think this time of year in MN the efan would never/very seldom come on (unless a/c compressor is on and the complete cooling system is in top notch condition) until late next Spring, early Summer. Sounds like the entire cooling system is due some TLC. <$250 buys all the parts, including a new rad.

The t-stat is the one item than can be removed (for test purposes only), and the vehicle driven, to test if the stat is the overheat culprit. While the stat is out, test it in a pan of water, using a cooking thermometer, on top of the stove. Do not toss the stat into boiling water....that tells u virtually nothing.

Thax

Id seriously suspect poor radiator and or water pump performance. I wouldnt rule out a Head Gasket failure until both combustion leak and compression tests are performed.

Radi

That's going to be unusable in the dead of winter with no defrost.
If the heater core rotted through, the radiator probably isn't far behind and the impellers on the water pump may no longer exist. I'd look at the water pump first. Your symptoms are consistent with diminished coolant flow.