If you are changing your coolant every 12 months you should not have to flush the system EVER!, as long as you use the same coolant ie only flush when changing coolant brand/type.
I would recomend replacing coolant every 2-4 years depending on the hours the machine is doing per year.
Water
Scale is usually caused by using hard (mineralised) water. If using distilled/RO/demineralised you should not have scale.
Coolant
Use a coolant concentrate suitable for your system - they are not all the same. If in doubt get a recommendation from Kubota/ a radiator repair shop/ well informed parts supply/etc.
Older machines with copper radiators use diffrent coolant to those with aluminium core radiators.
In general your 50:50 ratio is correct but check the instructions on the container.
The COLOUR OF THE COOLANT (green) IS NOT A INDICATION OF COMPATIBILITY with your system.
Thermostat
If fitted, replace it (& associated gasket). An old one may be sticking, inhibiting coolant flow + overheating.
Radiator Cap
Replace with correct cap (pressure rating).
If system fitted with expansion/overflow reservoir make sure the cap is correct for this system.
If no expansion reservoir, only fill your radiator so that the coolant covers the core (look in top) leave the "top tank" with an air space to accommodate coolant expansion when hot.
Radiator Hoses
If older than 5 years - replace.
If cooling system does not use an expansion tank - make sure bottom hose is reinforced to prevent collapse. This is usually a wire coil in the hose (can be reused) or a wire reinforcing in the material of the hose. When replacing coolant hoses do the lot, including the overflow/expansion tank hose
Radiator
After each mowing- use compressed air (NOT WATER) to clean radiator & screens (if fitted) to maintain good air flow
If for some reason you have contaminated your cooling system with a material that cause sludge/solids/scale to form -, You could try removing the radiator and back flushing it using your garden hose. If severely blocked, this may not help, you will need to get the radiator professionally flushed/cleaned out or purchase a new radiator.
Fan & Coolant Pump
Ensure the belt drive is in good condition and sufficiently tight so that manual turning of the fan is quite difficult.
Pump - any leak must fixed. In the past seals/bearing could be renewed, these days you replace the whole pump (get a gasket lit to suit).
Chaff screen
If fitted - Will require, at the very least, daily cleaning. In some conditions/machines, cleaning during the working day, may also be required.
Hope I have covered most of the areas that could give you overheating problems. Address one issue at a time. Start with the cheapest/easiest to do and see if that fixes your overheating, before moving to the next "fix" and so on
![Devil :devilish: :devilish:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)