I bought a 3/4" thick Permanent-cool trans cooler. The instructions say it must be installed in series with the radiator. They do not want the radiator by-passed. I bought a 15 x 7 cooler and planned on installing it between the A/C condensor and the radiator. I would think the size and location of the cooler would work better by-passing the radiator. So, why do they want the fluid running through the radiator and cooler?