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AW-4 Transmission Swap

Since the radiator was out of the running for transmission fluid cooling, I had to come up with something else.  Auxiliary coolers are often added to vehicles when they see trailer towing or other heavy duty service.  These are usually mounted up front in the air stream, just behind the vehicle's grill.  Mounting my cooler there would only add to the heat load of the radiator (sucking hotter air through the radiator won't make it cool better) so I decided to use two stacked plate fluid coolers to handle the tranny fluid cooling chores.


The first stacked plate cooler will act as a pre-cooler.  I call it my pre-cooler since the hot transmission fluid will encounter this cooler first upon leaving the AW-4.  It is my intention to mount this cooler in such a fashion as to get some air flow across the plates while the TJ is moving.  (yeah I know, not exactly a novel idea)  What I mean is that I hope this cooler will reduce the fluid temperature enough, during routine city/highway driving, such that the second cooler has less to do. (more on that below)  The core size of this unit is 2.5"x11"x1.5", which is not exceptionally large compared to many.  I ordered it from www.summitracing.com , part number BMM-70265.  Cost was about $46. 

I chose a stacked plate cooler design over the less expensive tube and fin type as they are more suited for off-highway use.  Stones and pebbles will have less of a tendency to damage this type of cooler.  If you've ever mounted/used a tube and fin cooler, you know it takes next to nothing to bend a bunch of the fins and thus reduce the air flow through the unit.  While I plan to mount the two coolers in the safest place I can, I still have to remember that the TJ is going to be playing in the rocks and brush.  The stacked plate coolers usually have integrated mounting tabs/brackets while tube and fin units end up getting held in place with zip ties and such. 


The second cooler is also a stacked plate model but comes equipped with a 12 volt fan.  This setup is designed to make its own air flow to cool things down.  This particular unit is slightly larger, with the core measuring 8.5"x6.5"x1.5".  The fan is thermostatically controlled and pushes air through the core at about 400 CFM when the fluid temp hits 175F degrees.  The fan cuts off at about 160F degrees.  Below that temperature, the fan is off.  It is my hope, as I mentioned earlier, that the pre-cooler will keep the fluid temperature low enough so that fan use is kept to a minimum, at least while doing city/highway driving.  The tranny fluid, upon leaving this cooler, is returned to the transmission.  I ordered it from www.summitracing.com , part number BMM-70298.  Cost was about $190.


I'm not betting the farm on my two stage fluid cooling configuration without being able to monitor just what is happening.  I picked up an Auto Meter transmission temperature gauge to take care of that task.  Heat is the worst enemy of an automatic transmission since it will drastically shorten the useful life of the transmission fluid.  Once the fluid has been overheated, your tranny suffers badly....it doesn't take that long before major problems surface.  This gauge comes with a remote sending unit that will be mounted in the tranny pan.  That will give me a good idea of what the average operating temp is of the fluid.  I picked up the gauge at a local performance shop.  I saw them listed on the Summit Racing web site for about $45.  The AutoMeter part # is 5757. 


More AW-4 Tranny Swap



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