how hot should aux tranny cooler be?

Just finished my aux transmission cooler install this evening (on my 06, with 3.5L engine). Everything did not go as I had originally intended and I ended up plumbing it in on the feed side of the radiator rather than the return line. There just was not enough space on the return side (top) of the radiator and I could not get my pipe cutter in there. Plus the routing out the "factory" hole in the radiator support was too small for my likeing if I tried to shoe horn 2 hoses through it.

Anyways I cut into the metal feed hose a few inches back from the 90 degree bend that goes into the bottom of the radiator. swivelled that piece around towards the passenger side and slipped on cooler hose number one. slipped number two onto the straight portion and fed them both around the air dam and up into the cooler mounted out front. Pretty simple (though it took me nearly 6 hours trying to figure all this out). Buttoned it all up and checked for leaks, all was good. Used lots of slightly larger diameter tubing to shield any possible chafe points. Took for a test drive, and man, that aux cooler gets HOT!! It was only 80 here today, no trailer load, just me in the car. Ran round the block, and for a nice long drive on the freeway. Cooler is too hot to touch, is this normal? I had to add 1 quart of fluid after this was complete, no leaks and the level is correct. engine temp is normal, just a hair above the half way point.

Those of you with it plumbed into the return line off the factory radiator, how hot does it get? I'm surprised it is soo hot, both the line going into the aux cooler and the one returning are nearly too hot to touch. I am using a B&M super cooler, stacked plate design rated for 13,500lbs.... I reached under the car, and the feed line from the transmission does not seem that hot? There is no way i'm somehow super heating the fluid by running it through a cooler is there? Its rated as a LPD (low pressure drop) unit specifically for transmission cooling. I have it mounted to the radiator support brace, not directly touching the condensor so there should be minimal heat transfer.

Let me know what you think, thanks! (sorry for the long post)

So the fluid goes from the trans first, then to the aux cooler, and then the radiator?

This is not ideal. The radiator, even the 'cool' side is very warm. You may be actually warming the fluid up by going through the radiator, and rendering the aux cooler useless.

For my vehicles, I use the biggest cooler that will fit. On 2 vehicles, I have by-passed the radiator entirely, and rely strictly on the aux cooler. The return line is warm, but never too hot to touch... I guess about 120 deg max.

If you can hold the return line with your hand for a long time without it becoming painful, chances are the return line is relatively cool, and you should be okay.

Found the cooler used in your vehicle at: http://www.bmracing.com/PRODUCTS/Automatic-Transmission-SuperCoolers/Automatic-Transmission-SuperCooler-rated-at-13-000-BTU-11x7-1-2x3-4

My local mechanic told me that all GM vans run hot. For my '09 Montana van, I installed a LPD cooler designed for an attached 5,000 lbs trailer. re: http://www.makcotransmissionparts.com/OC-1678.html

Even though I pull a max 3,500 lbs trailer (maybe 1 time per year for short distance), he told me to install an LPD cooler designed for attached 5,000 lbs trailer. Thus, help lowering its ATF temps on normal driving days as well.

Note: Your van's aux cooler and my van's aux cooler seem to be the same physical size. Hopefully, they are the same efficiency as well.

As MagicRat pointed out. The flow must be: Tranny, into main rad, out of main rad, into aux cooler, out of aux cooler and into tranny. This flow is also explained at: http://www.makcotransmissionparts.com/cooler-info.html re: Its red text stating "Transmission > Radiator cooler > Auxillary cooler > then Back to the transmission."

For pictures of my van's aux cooler install, surf:
http://i178.photobucket.com/albums/w251/Spike99-Pictures/Montana%20Van/AuxTransCooler-UpperSupport-1.jpg
http://i178.photobucket.com/albums/w251/Spike99-Pictures/Montana%20Van/AuxTransCooler-UpperSupport-2.jpg
http://i178.photobucket.com/albums/w251/Spike99-Pictures/Montana%20Van/AuxTransCooler-LowerSupport-1.jpg
http://i178.photobucket.com/albums/w251/Spike99-Pictures/Montana%20Van/Main-RadTophose-2.jpg

If wondering, my van's aux cooler is warm to touch. It isn't burning hot after a long trip. But, it is warm to touch. Thus, showing me it isn't beeing "over stressed" at all. Perhaps your aux cooler's flow is simply incorrect? Change the flow and see if "too hot to touch" problem still exists. When changing hoses around, blow inside your aux cooler lines as well. Hopefully, it its internal tubes is NOT blocked. Hopefully, you can blow air in/out of it with ease (after its ATF fluid is blown out of it).

Hope this helps..

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