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Message: [QUOTE="Mark Kovalsky, post: 53927, member: 1654"] The transmission cooler is on the "cool" side of the radiator. That is the side that the coolant has already been cooled by the radiator. It isn't at the engine temperature, it is quite a bit cooler. Isn't that why the radiator is there in the first place? In winter the "cool" side of the radiator is often close to outside temperature, nowhere near engine temperature. For three years of my 19 years at Ford I was a transmission cooling engineer. I measured all sorts of temperatures in these trucks in ambient temperatures from -40°F to +115°F. I never found a condition where the radiator cooler heated the transmission fluid. People talk about how the radiator heats the trans in the winter. When I measured the coolant temperature inside the radiator at near the transmission cooler we had to drill the radiator to mount thermocouples inside. That way we could read the coolant temp around the cooler. We also measured the ATF temperature in and out of the cooler. The ATF and coolant started out at the same temperature because the truck sat in a cooler at -40°F overnight. Once it started driving the ATF slowly warmed up. The coolant near the trans cooler also warmed up, but stayed cooler than the ATF. Which was heating which? Once the engine got hot enough to open the thermostat it only opened for a few seconds. We would see the "hot" side of the radiator temperature spike, but come down quickly. The "cold" side of the radiator never moved more than a couple degrees. The cold air hitting the radiator going down the road sucked all the heat out of the coolant before it got to the other side of the radiator. Back to the original question. I think a big part of the heating problem is a lack of a radiator cooler AND the cooler that's on the passenger side of the truck is a tube and fin cooler. That's one tube that snakes back and forth. Those are only good for adding restriction to the cooling circuit. They are poor at cooling the ATF. Replace both of those coolers with a 6.0L cooler and you'll do MUCH better. Even better than that, use the 6.0L cooler after the radiator cooler. Then you'll have bulletproof cooling. Mark [B]Former[/B] :fordoval: Automatic Transmission Engineer [/QUOTE]