If it is typical small garden I agree you should not have a problem.
But I am not sure you can assume that you can plow all day in hot weather with any HST without overheating problems. I know for a fact that you can't with a Kubota
L4330 in south Georgia in the summertime, because I have one. Perhaps it is an aberration, but I don't think Kubota really tested this tractor under extreme conditions. The grill design is very restrictive. I replaced it with a home made perforated metal grill that eliminates the lights and other plastic trim that interferes with airflow. That almost solved the problem. When I get a chance I am going to relocate the battery from right in front of the radiator to the FEL upright. I hope that completely solves the problem.
The
L4330 is a 43hp tractor. The HST, which uses a piston pump and piston motor (like most HST's), is about 75% efficient (the pump and motor are each about 85%). That means that at full load, of the 43hp leaving the engine, only 33hp reachs the transmission output shaft. The remaining 10hp is dissipated as heat in the transmission fluid. I don't have my hp to BTU/hr conversion table handy, but in the case of the
L4330 it is more than the cooling system can handle. First, the transmission fluid temp climbs towards 200 deg F. Then the coolant temp climbs to over 250 deg F (that's when the overheat warning light comes on).
That does not happen when I am using the rotary mower, because the majority of the engine power is going through the PTO system rather than the HST.