One, the TRX engines tend to run hot. I know the 2.5 is supposed to run on the cool side like most high performance engines, but you are about the tenth person who has mentioned having a 2.5 that seems to run hot.
Two, the hot day/cold day things is actually reversed. On hot days, running lean is a good thing and on cold days you want to run rich. The air density is lower on hot days so the engine actually gets "less air" by volume than on cold days. This means you need to adjust your mix accordingly...thus hot = lean and cold = rich.
Now to address the potential problem. Odds are you don't have a problem. Do you notice any decrease in performance? Does it just suddenly die after a while of running? If not, the engine is probably not overheating nor is it in danger of doing so.
The engine may be designed to run at a lower temperature, but the engineers will be the first to tell you that running hotter affects engine life in different ways (from not at all to catastrophic failure in a short time). There is no one right answer.
I would suggest going to either a higher nitro percentage (like 30%), adding a little castor oil to your fuel (do this to the gallon vice trying to add a teaspoon or something per tank), or richen up your settings (increased fuel adds oil and allows for a slightly cooler run) and see what happens.
When you get the problem resolved, let us know what solution worked.
