No idea why but it didn't cool my transmission oil 1 degree. I have a 6.0 cooler on my 7.3 and it works great. However, I put it on for extra cooling for cool upgrades while towing my big fifth wheel. I mounted it under the truck. I've since changed it to the front. But it still didn't help. I'm not sure why the principle seems simple enough. I don't want to shut down a product if I'm not sure why it's not working, will keep experimenting.