Heat is the #1 killer of transmissions, we all know that, the general consensus is that 170-190 degrees is optimal for 90% transmissions on the street, or 20-30 degrees below engine coolant temperature. Unfortunately, sometimes manufacturers cut corners and skimp out on things that cost the end user more money in maintenance at the end of the day.

This curse fell on 3rd generation W-bodies when they debuted in late 2003 with the 04+ Grand Prix, Lacrosse, Impala, and all other V6 vehicles on the platform. The 4T65E transmission they were all equipped with, an already questionable transmission in its stock form, likes to run hot, many owners reporting 220-230 degrees on warm days. This is due to an inferior transmission cooler inside the radiator, and this problem arose with the release of the 3rd generation, it was not a common issue before with the 88-03 1st and 2nd generation W-body cars.

Installing an auxiliary external cooler, inline, or standalone depending on your local climate, resolves this issue quite well, bringing those temps way back down to reasonable numbers. So that's precisely what I did with my Grand Prix in hopes to keep the modified transmission in good shape until I can afford a fully built unit, or swap it with a manual or the venerable 4T80.