Re: Kohler 9CC061-RV
If it is rubber mounted, check the mounts for any cracks or fatigue. Fortunately, it looks like the outer frame for the radiator is built very stout. If you have no history on the coolant, I would highly recommend doing a drain, light flush with citric acid granules and change the thermostat and any hoses that look in poor shape. I use Zerex G-05 and distilled water or better yet is the Zerex red diesel rated coolant and distilled water. Try to find the cooling system TOTAL capacity and then top it off with the distilled water. I say this because there is always some residual rinse water left in the engine. By putting 1/2 of total capacity of coolant FIRST, you are insured to get a 50/50 mixture.
I have used the citric acid flush since my Mercedes diesel days. Mercedes recommends it as a thorough but gentle cleanser that doesn't take out the water pump. If you need a water pump, change it now before the coolant change. Don't buy the pump or thermostat from Kohler but from YANMAR after market. Lots cheaper.
My 1939 WILLYS Pickup.
Bought in 1971