The most common reason for an N to “over heat” is over filling the radiator. Only add enough fluid to cover the core. (check out tip # 24, below as well as tips 25 & 35) It is not actually over heating; it is just spewing out the excess water.
If the radiator is not overfilled, check for low coolant, a loose fan belt, debris in the radiator fins or a stuck thermostat. A bad water pump will usually squeak or leak. (If you ever have a water pump start leaking or making noise, replace it immediately. A N water pump will come apart & launch the fan into the radiator.) And, unless you have a new/rebuilt water pump from a reputable source, it could have impeller erosion. The pump will turn, it won’t leak, but it isn’t circulating water.
In order to have a stuck thermostat, you need to have one installed. Squeeze the top hose; if it has a t-stat, you can feel it. Sometimes (rarely) the t-stat can migrate in the hose & get stuck closed. Or, in an attempt to keep that from happening, some owners will put a third clamp on the hose & tighten it too much resulting in a stuck t-stat. The OEM top hose came w/ a non-adjustable ban to keep the t-stat in place.
The fan belt should have 1/2" of flex at the mid-point; no more, no less.
Unless you have a pusher fan, blowing out the radiator from the engine side is always a good idea.
If none of that works, you may need to flush the radiator & block.
Get a can/bottle of cleaner from the parts store.
Remove the t-stat from the top hose. Reconnect the hose.
Pour the cleaner in the radiator & run the tractor to operating temp.
Then, remove the bottom hose from the radiator, stuff a rag in the bottom radiator hose connection, & stick your garden hose in the top of the radiator. Turn the water on (reverse flush) & the water will flow into the radiator, then the block & out of the disconnected lower hose. Let it run until the water is clear. Then, check the radiator flow. Stick the hose in the top of the radiator; the water should flow out of the bottom w/o backing up in the filler neck. It should flow at 19.5 gallons a minute. Don’t forget to put the t-stat back in correctly!
Use 50/50 anti-freeze & distilled water as your coolant. The anti-freeze contains rust inhibitors, pump lubricant & raises the boiling point of the coolant.
If you do need to get the radiator re-cored, make sure you get the flat fin industrial core. Automotive style cores will clog up w/ debris very quickly.