The small one is for power steering/brakes, the engine oil cooler is the large round tube on the side of the motor where the oil filter screws on.
As for tranny temps, I get worried at 200 and if it stays over 220 for more than a few minutes I'll pull over, or if it gets over 230 I'll stop immediately. After putting a Trucool 40K cooler on mine for $120 I have had no more temp problems. Also mine does not and did not go to the radiator. It had a cooler between the radiator and inner cooler which I upgraded to the Trucool 40k one like the v-10 has and I added a 40k Trucool cooler in series and mounted it to the back of the front bumper. Pulled a tractor yesterday and temps never even registered on my gauges.