Monday, September 3, 2012

I finally found the answer

Well after years of fighting an overheating jeep and replacing everything including the motor I believe I have finally found the problem.  As I have stated before I live in Dallas, Texas.  It only get to freezing temperatures a few days a year.  It got over 100 degrees last summer for several months.  If you live in the southern United States and have an automatic AW4 transmission and have tried everything under the sun to keep your jeep cool, you probably have the same issue as me.

Here it comes.  I have been running a B&M transmission cooler inline with my radiator "cooler" thinking that two things cooling the transmission are better than one, Right?  WRONG!!!!
The transmission lines going to your radiator are not designed to cool your transmission.  WHAT THE FU**....They are designed to warm up your transmission in very cold climates.  I LIVE IN DALLAS so I dont give a Sh** about warming up anything in this damn jeep.

I have a heat creeping problem on very hot days with the AC running.  There is something called "heat saturation"  This is when metal stuff like radiators cannot cool and begin to get hotter and hotter because there in not enough cold air passing through it.  Turning off the AC will bring it back to operating temps.  This tells me that the small load of the AC running is pushing the engine temps over their limit.  This tells me that my jeep is walking a fine line between good and bad.  This also tells me that a small change in load, airflow or coolant temperature should make all the difference that I need.

My transmission runs at about 160 degrees when air flow is good but gets up to 220 and slowly creeps higher when sitting in traffic or idling in a parking lot in the hot ass summer months.  This is about the same temperature as my engine...coincidence?

No, its not a coincidence because both the engine coolant and the transmission fluid cross pass each other in the radiator.  The engine wants to run at 210 degrees and the transmission wants to run at about 160 degrees.  Why would I want hot AW4 transmission fluid running across my engine coolant?  They find thermal equilibrium at 205 degrees and then both slowly creep up because of heat saturation.  Both the engine and tranny begin to overheat when sitting too long.

The answer, I believe has always been that I should have been running the transmission cooler in bypass of the radiator.  The B&M tranny cooler should "want" to keep the transmission at ambient temperature of 110 degrees instead of the 210 degrees that the engine "wants" to maintain.  With the transmission cooler bypassing  the radiator the engine coolant will have less thermal input and should help with the heat saturation problem.

I will put a new B&M tranny cooler in front of my condenser on the passenger side of the radiator since this side has shit loads of air flow provided by the mechanical fan.  (by the way, there is NO ELECTRIC FAN THAT CAN MATCH THE CFM AIRFLOW OF THE MECHANICAL FAN ON A XJ)  If you are having an overheating problem like me, spend it on a quality tranny cooler and bypass the radiator instead of a $400 triple electric fan setup.

I will post more with the results.....


  1. Hi! Did it help? Ive the same problem!!!!

  2. HI!!!! …. I did everything almost like you and still havent found a real solution. Di it work? …

  3. Did it work! I have the same issue.

  4. Did it work! I have the same issue.

  5. Hello.
    Did you ever fix the overheating problem? We have it constantly in the hot weather when in traffic or driving long periods of time (from Georgia to Florida) HOPE you found an answer, we have a trip coming up. Please let me know.

  6. I found a major factory defect in my over heating jeep....replaced the defected part an been running cool since

  7. Funny how many people have cooling issues with the Cherokee. I have a 97 that I have been battleing for the last 4 years and have spent well over a thousand dollars troubleshooting it. Ive come to the point where I will be taking the head off and seeing if there are any issues with the gasket, block, or head. If after rebuilding it and it doesn't solve my issue I'm saving up and dropping a LS motor in.

  8. Thanks for sharing this amazing and beautiful article. I would love these ideas.

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