John Deere 800 Swather Running Hot

My JD 800 swather is running hot about 10 minutes into the start of cutting my alfalfa. I have cleaned the radiator fins and the coolant looks normal. What else should I be looking at? Thanks for any help.

Thermostat, is the radiator hot or just the block?

Is the fan belt tight?

To get hot within 10 minutes is concerning.

Is it actually hot by the gauge, or is it blowing coolant out the overflow?

If it's getting hot that quick, sounds like there is no circulation. That can be caused by a defective thermostat, internally clogged radiator, or in rare cases loose or broken pump impeller.

Is the air coming through the radiator hot? If no, there is no circulation. The upper tank should be too hot to touch, the lower tank considerably cooler. Feeling the radiator core, you should feel uniform heat, no cold spots. Cold spots indicate blocked passages.

If the coolant is blowing out the overflow before the temp actually reaches the boiling point, that is an indication of combustion gasses entering the cooling system, as in a blown head gasket or cracked head. Other symptoms are mystery coolant loss, steaming exhaust on a warm day, water condensing in the crankcase, misfire, hard starting as in locked engine when trying to crank.

Early on, not all symptoms will show, it can be difficult to see any, but still it tends to overheat. Try removing the plugs, let sit with pressure on the cooling system overnight. Crank it through and watch for coolant to blow out a cylinder. A combustion leakage test will sometimes be needed.
Combustion Leak Detector

Drain the coolant and flush the radiator and the block and you?d be surprised how dirty it really is

Bad thermostat or a clogged cooling system either one can cause that. A cooling system flush with vinegar will help if clogged

Late timing can cause overheating as well.

Ben

Steve, that is the best overheating troubleshooting procedure I have ever seen. Thanks!

I will start by flushing out the radiator and replacing the thermostat. Can anyone tell me the part number of the thermostat and where I can get one? Thank you guys for all your help.

Steve@Advance - It is getting hot by the gauge. The needle goes up past the normal operating position to the hot line on the gauge. Once it reaches that point, that is when I stop and let it run for a bit before I shut it off. Once I shut it off, and let it cool back down to at least the normal operating temp (per the gauge), it will not start again. It has to cool all the way down before it will start. The top of the radiator gets hot, not sure about the bottom yet.

You can test the thermostat in a pan of water and a thermometer. Heat up the water and watch and see at what temperature the thermostat opens. The thermostat may or may not be the problem. To test for a bad head gasket, put the overflow hose in a glass of water. Start the engine while it is cold. If you see bubbles, the head gasket is bad.