Folks, the oil to water is a key part of the cooling process. In the winter or cooler months, the engine gets the trans fluid to temp. It is VERY BAD to operate a trans regularly under 160 degrees. A trans works on the princ of friction. Too cold can do similar damage as too hot. The sweet temps for a trans is between 160-185 degrees. The oil to water is not designed to cool the trans very much, but more to take the edge off or help provide heat in the cooler months. It will not usually add trans temps as has been described unless you have a run away engine cooling issue where the engine is pushing 260 degrees (which is not normal). Even then, at those temps it would not push the trans to 260 degrees for a while, if at all. This thought that it can is flawed logic.
How do I know this, well from mechanics, car club forums where this has been debated over and over and over and from my direct, personal, real world experience? I had a 185 degree thermostat on my prev tow vehicle (GCVW or 11685lbs). The engine (a 350ci) would regularly get between 195 to 205 degrees. The trans (4L60E) would get upwards (per the gauge I installed for the trans temps) 190 degrees (keep in mind this is with a the trans going into the radiator, then to an external cooler and then back to the trans where the temp sending unit is located).
So then I placed a 160 degree thermostat in the car. The engine temps lowered to between 175-188 degrees (depending on towing and outside temps, A/C on or not). The trans pretty much stayed the same as it did when I had the 185 degree thermostat in the car, maybe lost 2-3 degrees on the best days.
Adding a better cooler or in my case an additional oil to air cooler dropped my trans temps to between 170-175 on average, warm outside, towing. Sure it peaked to near 200 when moving 11,685lbs up a hill, but it would come right back down to about 175 towing and 160-165 not towing on very warm days. Cold days not towing the trans would park right at 160 and cold days towing, stay at between 165-170. Even though when I tow the car engine temps per the PCM (not the temp gauge) clearly showed when towing the 6300lb Safari, that the engine temps were near 190 degrees, the trans rarely got above 175 degrees.
That said, leave the trans oil to water connections alone. Fix your cooling problem and add a good external trans oil to air cooler and you will be VERY happy with the end results. I spent over a year playing around with engine and trans temps. Feel free to do all the testing and hit or miss on your own as some aspects will be unique to your need.
Two additional suggestions when it comes to trans cooling. Make your torque converter cover look like this one:
(Click on the Neal Torque Converter Cover for pics)
This particular one was made for the 4L60E, but you can see the princ of why to do it the second you see the old one. This cover allows air to pass the torque converter. The stock one is a closed cover, and acts like a blanket, trapping heat and increasing trans temps. It may only cool it a degree or 2, but for $50 if you can find one for your app or spending the time to make a custom one, is well worth it, particularly if you do it in conjunction with the next suggestion.
Find and install a deep pan kit for your trans. It can add upwards of 2 extra quarts to the trans pan. It's a no brainer.....To me the thought was sound. If you place 2 similar pots of water, oil, whatever on a stove. One is half full, the other is 3/4 full and turn the stove on to full heat, the pot that is half full will boil or reach temp faster as there is less volume to heat.
The same holds true in the trans. Adding more fluid makes it more difficult for the fluid to take one for the team when flash heat is applied (taking the load up a fair grade).
So the reader's digest of all this is:
-Don't mess with the rad tank trans cooler
-Get a great external trans cooler and add it in line with the rad cooler
-Modify or buy a torque converter cover to release boxed in heat
-Get a deep trans pan kit (with required deep well filter) to make it take longer to heat the trans and deal with flash load creating heat)
- Find out why your engine is overheating and fix that problem
- Look into an experiment with a 160 degree thermostat, knowing that if you drive in the colder months, you might need to restrict airflow to get the engine to come to temp.