Help!!!overheating!!!

My xj reaches 240-260 degree temps when driving on hot days or uphill. I have replaced the radiator (installed 2row modine), water pump, tstat, belts, hoses, fan clutch. I did a cylinder leakdown test, so i know the head gasket is good. What else could it be? is there something i am missing? i have never worked on a jeep 4.0. any info will be helpful. thanks

Catalytic converter?

Could the A/C thing (can't think of the word) in front of the radiator plugged up with bugs? Is the radiator getting plenty of air? Is your fan shroud in good condition? Is the aux fan working properly? What kind of fan clutch did you install? Apparently, some of them are worthless.

red96 said:

My xj reaches 240-260 degree temps when driving on hot days or uphill. I have replaced the radiator (installed 2row modine), water pump, tstat, belts, hoses, fan clutch. I did a cylinder leakdown test, so i know the head gasket is good. What else could it be? is there something i am missing? i have never worked on a jeep 4.0. any info will be helpful. thanks

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Are you sure it's really that hot? At 260 you would be blowing all the water out.

ok ive been through this before first of all what year is it second does it have a expansion tank or is it a real radiator

The 4.0 is a Problem Child for overheating.

The A/C condensor is located dierctly in front of the Radi and if not clean can cause flow issues. Also the Cat can be a issue if getting plugged.. thus not allowing the exhaust to escape and building up heat.

Going through overheating is something every XJ owner will have to do at some point. I would check that the fan shroud is intact and free from cracks. Also pull the stock thermostate and replace with a lower temp... 180* should do OK. Still make sure you get a high flow thermostate! Taking a dremel to your thermostate housing can also help the flow in this area but remember that it is cast alumi and is thin in some areas.
I also run a High flow water pump. It is called a FlowKooler and produces the same flow at low RPM as it does at highway RPM.
The electric fan may also be a issue. Make sure it is coming on as it should with the A/C off.
There is 2 sensors to really be worried about the first is a samll one on the rear of the block on the drivers side. This is the sensor for the gauge itself yet feeds info to the computer. The other is the major one. This one is the one in the theromstate housing. I am unsure as to how to test these. I just replaced mine after the last engine swap.
:repair:
This is also something that most people don't think of. The O2 sensor. Being that it controls the fuel as such it ialso tells the computer when things are hot. This might also be a issue.

xjfreak95 said:

ok ive been through this before first of all what year is it second does it have a expansion tank or is it a real radiator

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Being a 96 he has a real Radi.

IF the rig gets to 240 then pull over, full blast the heater and let it idle for a few mins before shutting down to cool. DON'T run it with the temp taged out. Going to the 260 range is asking to blow the engine up.
Yet if your running it with the temp gauge taged out then it might be the rear senor on the block just not reading right.

its the real open system radiator. I changed the temp sender and put in an autometer watertemp gauge cuz i thought the stock one was reading wrong. when the gauge reads about 225 the actual water temp in the radiator reads about 20-30 degrees cooler. it has never boiled over. i have a 180 tstat which helped a little. it also isnt throwing any codes but i may as well replace the o2 sensor since it has near 150000 mi on it. thanks for the help!! any other info will be much appreciated

If you have changed radiator, pump, and other things that need or cause a refrigerant loss (water, antifreeze or whatever you are using) the engine does not get all the water in when you refill the radiator, it means AIR GETS TRAPPED INSIDE the engine mainly on the motor head where the sensor (the one in the back of the engine at the driver side is located) has to read the temp, then it will read much higher HEAD temps not water temp, thats why you get a 260º reading and the engine is not boiling.

You have to purge the air from the engine, locate the temp sensor (driver side, at the back, in the head) unplug the connector, use a deep socket wrench and remove the sensor, fill with water until all air bubbles are out then reinstall the sensor, do not overtighten or you will break it , reconect the sensor and I'm sure your problem will be solved.

I went through the same problem and thats the solution that these folks gave me and IT WORKED.

Good luck

SACEM

Sacum - did this solve your overheating problem or did it fix your temperature sending sensor issue? I am curious because I have the same overheating issues only on VERY hot days on the highway and up hills - and I will boil over. I have done lots of searches in this forum but there seems to be no consensus of what might be going on. I have twin electric fans, flowcooler water pump, high flow thermo housing, GDI 3 core radiator, etc but I will still boil over. So is it that I have air in my system? Thanks!

sacem said:

If you have changed radiator, pump, and other things that need or cause a refrigerant loss (water, antifreeze or whatever you are using) the engine does not get all the water in when you refill the radiator, it means AIR GETS TRAPPED INSIDE the engine mainly on the motor head where the sensor (the one in the back of the engine at the driver side is located) has to read the temp, then it will read much higher HEAD temps not water temp, thats why you get a 260º reading and the engine is not boiling.

You have to purge the air from the engine, locate the temp sensor (driver side, at the back, in the head) unplug the connector, use a deep socket wrench and remove the sensor, fill with water until all air bubbles are out then reinstall the sensor, do not overtighten or you will break it , reconect the sensor and I'm sure your problem will be solved.

I went through the same problem and thats the solution that these folks gave me and IT WORKED.

Good luck

SACEM

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What you described sounds like what happens with the older cooling systems: I've successfully fully drained mine and refilled it without having to jump through hoops.

Onkover said:

Also pull the stock thermostate and replace with a lower temp... 180* should do OK.

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Ummm all you're doing is proloing the delusional feeling of it being ok. The fact that tstat opens up earlier means that your coolant with start earlier on the longer run and then it won't be heating up (or rather overheating) as fast as before, but it will still do it.

red96 said:

My xj reaches 240-260 degree temps when driving on hot days or uphill. I have replaced the radiator (installed 2row modine), water pump, tstat, belts, hoses, fan clutch. I did a cylinder leakdown test, so i know the head gasket is good. What else could it be? is there something i am missing? i have never worked on a jeep 4.0. any info will be helpful. thanks

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Check your lower hose. It might be collapsing on you causing the flow to be diminished. While the dealer hoses have a spring in them, I've successfully used aftermarket hoses without one, while others had to get "spring loaded" hoses.

You swapped a lot of things: did you do it to fix the problems or was it part of maintenance? Did you do one item at a time? How long does it take before it heats up? You sure you got the right water pump? THere are some earlier jeep water pumps that look identical to a 4.0 pump, but they have a reversed water flow (look for an arrow imprinted on the inside of the pump). ALso when you installed pump and tstat housing did you use provided gaskets or did you use gasket maker? I've heard a story of someone overdoing on the silicon which then ended up clogging the radiator.

Also your temp sensor might just be bad: something worth looking into.

edit: Oh... this may sound stupid, but did you put in the tstat in the right direction?

I do sort of agree with that. Running a lower temp tsat does a few bad things but better in the long run.. I think personally. It doesn't let the coolant set in the radi as long there for not letting it cool as much as a 190* would. It just keeps a more even temp rather then up and down and up and down and....

Still your attempting to fool the computer doing stuff like this too.

Onkover said:

I do sort of agree with that. Running a lower temp tsat does a few bad things but better in the long run.. I think personally. It doesn't let the coolant set in the radi as long there for not letting it cool as much as a 190* would. It just keeps a more even temp rather then up and down and up and down and....

Still your attempting to fool the computer doing stuff like this too.

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So you're saying that a lower tstat is bad a little bit but overall good? If so, you might want to rethink that: in a working cooling system it means that your engine will run under it's expectant operating temp resulting in poorer overall performance. If you search on the OEM forum, you'll find that the topic has been covered pretty thoroughly.

TexasComanche said:

Sacum - did this solve your overheating problem or did it fix your temperature sending sensor issue? I am curious because I have the same overheating issues only on VERY hot days on the highway and up hills - and I will boil over. I have done lots of searches in this forum but there seems to be no consensus of what might be going on. I have twin electric fans, flowcooler water pump, high flow thermo housing, GDI 3 core radiator, etc but I will still boil over. So is it that I have air in my system? Thanks!

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Filling up with coolant and purging out the air solved the overheating problem and by default the head was with a lower temp and the gauge read the correct water temp as it was really in contact with the cooling water.

Sure several other modifications besides filling with coolant and purging the air out will help:

1) A double row radiator or better yet a 3 row one

2) A manual switch that takes ground current (neg) to the electric fan relay so that you can turn it on at will and keep temp from creeping up when wheeling or uphill driving.

3) Radiator hoses that can not colapse (rigid enough or with inner spring)

4) Correct pressure cap for the rad (16 psi)

5) A clean unobstructed radiator (wash it from inside out with a small 90º nozzle at the hose so that you can fit it between the radiator and engine)

6) Check the fan clutch, it should engage when temp in the radiator rises and freewheel when temp is lower, that for theory I have not been able to find a way of checking it yet. If in doubt you will have to fit a new one just to be sure.

That I think is a recolection of my own experience and that express in several threads in here if someone can add some more lines we can give it as an "General XJ overheating fix"

That said we assume you have an engine that is tuned correctly and in fairly good running condition without major operating problems.

Have a COOL ride

SACEM

I boiled my 91 :flamemad: at 260 on a long uphill trail ride on a 90+ day :rattle: with the original radiator. The only two things I did was replace my radiator with a new 2 row and I installed a relay and a switch to the aux electric fan. Once I get on a trail at slow speeds, I flip the switch and I never go over 220. :laugh3: :laugh3:

This might be an obvious question, but is your aux fan going on when (a) A/C is on, (b) defroster is on, and (c) engine temps reach 218*. If your '96 is like mine, you have an AC condenser and tranny cooler in front of the rad and you need as much air flow as possible. The aux fan (newer OEM type or better) is critical. The fan clutch could be junk, too, but unlikely. If aux fan works as designed, then I would flush the rad thoroughly in case there was any factory debris in the core. Listen to Kejtar, his suggestion on the lower spring'd hose is worth looking at as well.

Thanks for your input. My 95+ style aux fan does work properly and I do have an electric fan in place of my clutch fan. My personal feeling is that there must be a problem with my GDI 3 core rad because this only occurs on hills on the highway in hot weather and as GOJEEP says, he runs all day in the 100+ heat and his fans do not even come on. I can sit in idle traffic on 100+ days and it cools just fine. To give you the whole story - I did just add air cond to my comanche and this added a condenser in front but it was in decent condition. I found the rad purge article interesting and I plan on doing this soon. If that does not work I am probably going to purchase a Modine rad. and see how that works. Frustrating problem though. Thanks again.

A lower temperature thermostat will simply set the minimum operating coolant temperature. Meaning once the engine warms up, 180 should be the lowest the temperature drops. It will keep your engine running cooler(at 180F) but only on cooler days.

On warm days the temperature will still continue to rise until the temperature stabilizes due to the air passing through the radiator and consequently cooling the coolant(performing it's heat transfer job). At idle the electric fan will keep the temperature from getting too high.

Is there a 50/50 mix of coolant and water in the radiator?

It's possible that the thermostat may not be opening completely and limits the flow which would decrease the heat transfer at the radiator and consequently cause the cherokee to overheat.

One thing that can be done as an experiment is to remove the thermostat completely and let the engine warm up and run it in the situation where it used to overheat.(it will take a long time to warm up) If it doesn't overheat, the thermostat was the problem and it should be replaced with a new one. If the overheating still occurs, you need to look elsewhere and replace the thermostat.

MAP