Yes, Another Overheating Thread

1998 Cherokee XJ 4.0, Auto, A/C, 6 inch lift, 31" tires, 3.55 gears, winch below line of radiator, 7" lights that are mounted in front of grill but have about 6" clearance.
Well I am about to get out the :explosion and make this thing go away for good. First off I am sorry to bring in another overheating thread... This one has got me stumped.

Everything I have done does not change anything at all. I have replaced the radiator with a 3 core, replaced thermostat with factory, had cooling system flushed, removed head and checked all passages, head was warped .005 so had it milled, verified fans are functioning, cleaned fins on condensor and verified that it flows with both water and flashlight, removed lights from front to help airflow, replaced coolant/water several times burping each time, removed cat converter thinking it was plugged all to no difference at all.

It runs at the line that is past 210 but cools below 210 when coasting down a long hill.

I am lost on this one any ideas will be welcomed...the next step is replacing the motor and at this point it is the only thing left that I can think of.

Have you tried testing the CTS? Your 98 the PCM controls the gauge based on data from the CTS--in other words ARE YOU REALLY overheating?

Should be a threaded hole in the block, under the manifolds. Pull the plug, install a sending unit for an aftermarket temperature gauge, hook up the aftermarket temperature gauge, and find out exactly how hot your coolant is getting. You have done everything else, why not give that a try. Your CTS could be a little whacky, or the PCM output to the gauge could be whacky.

Thanks Joe, I will give that a shot. The only thing that is bothering me is it did actually puke its guts out the other day but that was before the head work and there was combustion gas in the cooling system according to my Block Check so I may have had more than one issue going on.

Ok, be sure and post up what you find.

Is a new water pump too obvious a suggestion ? While you are in there, replace the mechanical fan Clutch.

I forgot to mention that I replaced the waterpump too with a factory unit. Also, I verified that the mechanical fan is working by allowing it to warm up and then checking to see if the spinning resistance increased and it did then I checked to see if the amount of air being pulled through the radiator was normal. Keep the suggestions coming because as mentioned I am stumped...right now I am off to the parts store for standalone temp gauge to check actual temp...BRB

Picked up a infrared temp gauge and found that it is sitting at idle at 226 on the thermostat housing, 216 on the upper hose, right radiator tank 212, left tank 208, lower radiator hose 209 and water pump 213.

The gauge is showing right between 210 and the first line this entire time.

Ambient temp is 109

A/C is running and aux fan is staying on.

I asume that the metal parts on the block and head are going to pick up heat from those parts so that may explain why they are hotter.

There are no leaks and vehicle is running smooth with no loss of power.

What's your oil level? The oil system is designed to help cool the engine as well as lubricate it.

Also, do you have the right psi cap on the radiator? When the head was off did you magnflux it to look for cracks? You said you had it milled and checked the water ports, just didn't know if you checked for cracks

IBlameTheDog said:

Ambient temp is 109.

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given the fact of the hot ass temp, running 10-20* over the 210 mark isnt too bad. around here on a high 90's day while on the trail all day, ill run between 210 and the next mark. while its running hotter the usual, thats not in the range of overheating though. considering the temp outside and the stress being put on the jeep, its doin its job OK.

i should hook up my aux fan override switch and see how that does with the two 10" fans :greensmok

The machine shop checked for cracks and pressure tested it. The oil is within a month old and up to normal level and the radiator cap is new and 16 psi. I have had other Jeeps and they never went past 210 so that is why I am concerned. I am thinking I should drive it until it fails or hopefully it doesn't??? :banghead:

Given the weather conditions ... going up long hills ... and having the AC on ...

It sounds like the vehicle is behaving exactly as it should ....... according to the FSM.

Which is a bit surprising given you have fitted a better radiator ... as one would expect better cooling & slightly lower temp down around 200' from my experience.

Are your temps highway driving or offroading temps.


Im thinking:

Verify temp sensor/dash temps as per joe_peters said.

Fanclutch ... Working - but not as effectively as it should be.

Thermostat maybe not opening fully ... or fully open, soon enough. Operating specs and quality can be enough to cause ... or solve issues.

The particular 3 row design radiator you have - is actually restricting airflow/cooling ??? ... It happens sometimes.

Gearbox oil temps ....... and engine oil as previously mentioned ???

Fan over-ride switch is a good idea ... as its much better to have it providing the extra cooling ... BEFORE overheating occurs.

Anti-Freeze mix ... Hows your minimum daytime temps ???? High enough to run 30/70 or less - instead of 50/50 during the hotter weather ??


My stock height and tyred, 1998 RHD in 109' temps runs ...... 195' after some simple adjustments ....

:cheers:

If you are driving around in 109 temp I would suggest you do a HD fan clutch mod, it's noisy but it will bring your temp down.

I went ahead and ordered the HD fan clutch so hopefully that will help. The part is only 45 dollars so it really will not hurt anything if it does not help. As far as the noise goes I definitely would not hear it over my tires so I am good there. Thanks everyone I will post results once the clutch is in.

IBlameTheDog said:

I forgot to mention that I replaced the waterpump too with a factory unit.

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I have heard of people getting the wrong water pump with the fins inside the pump running the wrong way.
Could this be the case?

B.RAIDER said:

I have heard of people getting the wrong water pump with the fins inside the pump running the wrong way.
Could this be the case?

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Not a bad suggestion, but I think his problems would be worse.

I am not a big fan of coolant restriction, however it can have its uses. Here is a link to GoJeeps website: http://go.jeep-xj.info/HowtoRadiatorRestrictor.htm

The theory behind the restrictor, as it would apply to you, is the coolant is passing through the radiator so fast it has insufficient time to exchange heat--so you run hotter. This was found years ago with larger capacity radiators and high flow water pumps/thermostats giving to fast of flow.

Lastly, do some searching as others have posted up their temps at different points in the engine compartment/engine using the guns, that could give you a base line.

Good luck.

Is your belt tight enough?
It doesn't take too much slack to start affecting things.
If your fan-clutch is startin' to go out it can only compound the problem.

Have you picked all of the bugs & crap out of your condenser and straightened
the fins with a dental pick? Don't laugh, this can sometimes make a very significant
difference.

Is you auxilliary fan running the right direction? Saw one wired-in backwards, once.

You might also try divorcing your tranny from the in-radiator cooler and route an
external, especially since you're running 31s on stock gearing.

I would suggest you take a look at the new radiator again. I put a new 3 core in my XJ and it over heat worse that it did with the old one. It appearsthat many of the tubes werre blocked during manufacturing thus reducing the efficiency of the unit. Also, double check the new thermostat.

You did give the temps of various areas of the engine. Was this before a run or after a run? With the AW4 in the equation, could this be contributing to the high temperature?

Try removing the thermostat and then running the engine without it. Temps should be a bit lower if the thermostat is the problem. Also, what are the temps like without the ac on?

If the temps are unchanged, have the rad tested. Even though it's new, it could still be clogged as techno1154 pointed out.

joe_peters said:

I am not a big fan of coolant restriction, .........................

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Me neither ...
Id rather refit a stock pump ....... than bandaid with a restrictor, to make an unsuitable pump work.

techno1154 said:

I would suggest you take a look at the new radiator again. I put a new 3 core in my XJ and it over heat worse that it did with the old one. It appearsthat many of the tubes werre blocked during manufacturing thus reducing the efficiency of the unit. Also, double check the new thermostat.

You did give the temps of various areas of the engine. Was this before a run or after a run? With the AW4 in the equation, could this be contributing to the high temperature?

Click to expand...

Radiator was one of my earlier thoughts too ... especially if those IR temps are correct .... Doesnt seem to be a lot of variation between the inlet and outlet, radiator ends ???