Jowett

Again, why does Toyota want an 8.5 CST at "normal" operating temps for an engine with same requirements? Why not run 0W30 for slightly better low temp performance?

The trans cooler is awesomely large and works great while moving, but Toyota opted to save a few $ on the Tundra and eliminate the oil to liquid cooler in the lower radiator tank (Land Cruiser has it). After burning up tons of WS fluid (because it can't be inspected easily) and loosing enough money to blown transmissions, they moved the monster cooler in front of the radiator so the fan can keep it cool at lower speeds. Unfortunately, this now preheats some of the air that flows through the radiator... likely causing engine oil temps to run a smidgen higher.