Newbie here, getting to grips with a new (to me) Toro 4500D. Radiator grills are clear (all three of them), new blades, but it is still getting pretty warm - well into the red - after 30 mins running. A pretty early machine, 5700 hours, coolant level OK and system seems to be working (85F going into the radiator, about 75F coming out) Machine cools down pretty quickly if left for a few minutes on idle with the hood up. Any suggestions about what should I check next?