I have a Kioti DK45 tractor, and it's been overheating lately. Coolant isn't low, so, I figured I'd replace the thermostat. The one on the left is the new part (obviously wrong) but it does fit and is rated at the same temp. The question that I have, what is the part hanging down on the one on the right. I assume it's important.

if you have a candy thermometer or similar, heat some water to the temp or just above of what it is rated for, ie. 185 then go to 190 or so and hotter is not a problem

if it opens then use it. only way to truly test a thermostat.

the dual springs are to open/close, positive pressure on both sides. it is probably more efficient.

also, open the hood, check that the radiator and ac radiators are not clogged with chit.

I have to clean our jd 2-3 times a day when mowing.

I did put both the new and old in boiling water. They both opened to the same width, but the old one closed faster as the water was cooling down. I didn't use a thermometer. I have checked and cleaned the radiator and radiator screen and it doesn't help.

Thermostat is very rarely the cause of overheating. It's a Korean tractor so I have no idea how it works but Asians love using dumb ways to drive their water pumps. Might look and see if it's belt driven or internally driven. Air flow has been mentioned. Other than fluid and air flow, a head gasket, etc. is next in line.

I have ruled out air flow and fluid. I'll check the water pump next time I'm down there. It heats up to normal operating temp and hangs there for a bit, then starts to creep up. I first noticed it at the end of last summer. Then over the winter, I t didn't have an issue (obviously because of lower ambient temp). Now, it's overheating again. If I turn off the AC and PTO, the temp does come back down.

you might try running some good radiator flush with no thermostat. sounds like you may have some passages partially blocked.

Update: I think gasguzzler hit the nail on the head. Put the new thermostat in today. Also checked the water pump. It is belt driven and the belt was a bit loose. Tightened the belt and then went and mowed some really thick grass in 100 degree heat with the AC cranking. Tractor never got hot. I can't tell for sure which was the fix, but I suspect it was the loose belt, not the new thermostat that fixed it. Thanks GasGuzzler.

Good to hear.