XJ Automatic Transmission Cooler
	Category:	Performance
	Author:	MachineMan
	Date:	June 7th, 2005

This write up explains how to install an aftermarket automatic transmission cooler in your Jeep Cherokee. The write up is based off a 1990 Cherokee 4x4 with AW4 auto transmission, other years may vary slightly. This is an easy way to get additional cooling for your transmission fluid and will aid in extending the life of your transmission. Disclaimer – If your trans is running extremely hot there may be other factors contributing to your heat problem. Adding and external cooler may not solve your problem.

Jeep Tech
It’s not uncommon for Jeep Cherokee auto transmissions to run hot. In some cases overheating the trans will result in fluid leakage out the front or rear seals. An occasional heat induced leak shouldn’t create permanent problems but if it persists or occurs under light loads additional cooling or transmission service might be needed. When the transmission leaks fluid under heavy use it could be an indication overheating. The use of transmission temp gauge put inline with the ATF cooler line out is the best way to monitor your temps.

The stock cooler is a heat exchanger inside the engine coolant radiator. Some Jeep models with the tow package may already come stock with an additional air cooler up front. Fluid heat exchangers are more efficient than air exchangers except that the radiator coolant temps can exceed 190F in normal conditions limiting the amount you can cool your tranny fluid. On the other hand if you live in extremely cold climates this may be a benefit by helping to warm up the ATF to operating temperature. These are things that you will have to consider when installing a cooler. It can be plumbed in series after the radiator exchanger or plumbed separately eliminating the radiator all together. After much research it seems that excluding the radiator exchanger is the more popular route.

If your running 33" or bigger tires the tranny will be under much more load and tend to slip which generates lots of heat. In this case keep the radiator ATF exchanger plumbed in series before transmission cooler.

Parts
You can do this modification for around $40 to $70 depending on what cooler you choose and how you connect the cooling lines. It can be done for much less if you have Air Conditioning and choose to use the condenser as your tranny cooler, thus eliminating the use of you’re A/C unit. There are several different coolers available that will fit under the front grill of your XJ. If you have A/C and choose to keep it, than consider getting a cooler thickness that doesn’t exceed ¾ inch. It will fit in front of the A/C condenser and beneath the grill. Most tube and fin coolers will cost <$50 and can be purchased at your local auto parts store or online at www.summitracing.com or www.jegs.com. The bigger the cooler the better for your trans but more restricting for engine cooling. So choose what’s best as air will still pass through all of the stacked components. Plate coolers are said to be better than tube-fin units but cost more and might not fit under the grill with an A/C condenser. Its easy to take the grill off and do some measurement prior to choosing the correct cooler size.

To connect the cooler you will need to get at least 6 feet of 3/8 inch transmission cooler hose from an auto parts store and some hose clamps. Don’t use regular fuel, vacuum, or coolant hose. Also you will need some cooler mounting rods which can pass through the radiator to fasten the cooler.

Parts List
Oil cooler – Pick cooler that best fits. (7.5 x 17 x 0.75 inches fit my ‘90 with A/C condenser but you can go longer for more cooling)

Aftermarket Tranny Cooler (Derale)

Hose – 3/8 transmission cooler line (at least 6 feet)
Hose clamps - recommend 6 clamps (if not clamps, than use compression or flare fittings)
Cooler mounting rods – Derale makes some nylon and metal ones.

Grille Removal

Installation

1. Start by letting your vehicle cool some if hot, then remove the 8 screws holding the front grill in place.
   
   
   Cooler Lines
   
2. Disconnect the transmission flex lines from under the front of the engine. If they still have the stock quick disconnects then squeeze both tangs and jiggle the hose in and out until it pops off. Remove all of the quick disconnect retainers since you won’t be using them anymore. The lines are not under pressure but some fluid will drain out so be prepared. On the AW4 transmission the ATF out line is the one coming out of the front on the trans closer to the bell housing.
   
   
   Radiator Exchanger Connections
   
3. Remove the trans cooler lines from the Radiator exchanger in the same manor. After the fluid has drained from the exchanger put some sort of caps over the exchanger holes to protect it them from dirt incase you might want to use it again in the future.
   
   
   
   
4. Run your 3/8inch cooler lines from the front grill area to the hard ATF lines under the engine front. The lines can follow a similar path as the old ones but loop around to the front of the radiator. Make sure there clear of the engine pulleys and any sharp edges.
   
   
   Cooler installed
   
5. Connect the lines under the engine. The stock hard lines don’t have hose barbs so its best if you can push the rubber lines up past that quick disconnect retainer lip. Attached using 2 hose clamps per side for added strength. CAUTION: If you can not get the hose over that retainer lip then there’s no barb to help hold it on under pressure. It might be OK but not recommended. For a better connection consider installing some compression or flared AN fittings instead.
   
6. Cut to length and hook the hoses up to the new transmission cooler. Put the fluid supply (Trans out) line at the top. If the cooler has a barb then use a hose clamp. I found it easer to hook up the lines to the cooler before installing because it was hard top push the hoses on when mounted.
   
7. Now fasten the cooler to the Radiator (or AC condenser if equipped) using the push through mounting rods. Do not mount the cooler directly to the radiator (or A/C condenser) because constant rubbing and vibration may cause damage. I cut some rubber spacers out of some fuel line to keep the parts separated. You might have to remove the fan assembly on the engine side of your radiator to push, adjust, and trim the mount rods.
   
   
   Transmission cooler behind grille
   
8. Tighten everything up, secure the hoses where needed, and double check all your connections.
   
9. Start up the vehicle and run through the gears to circulated ATF fluid. Check your tranny fluid level incase you spilt too much. Inspect for leaks.
   
10. If it’s all good then put the front grill back on and your all set.
    

Automatic Trans Fluid Temperature Chart (from HECAT inc.)

Nylon Mounting Rods (Derale #16744)
Options and Upgrades

1. Some people also install an inline transmission filter.
2. For better cooling line installation, buy a cooler with compression fittings or AN fittings. Then install similar fittings onto the stock ATF hardlines. This will make for a cleaner and stronger set-up.
   
3. Build some mount brackets for the cooler which will be stronger than those push through rod fasteners.
   
4. Install an inline transmission temperature gauge.
   

Tom K. March 2005