overheating and the coolant system

I have a 1959 Fordson Dexta 3 cyl. diesel. I tried plowing with it in the wrong gear (3rd low) but it overheated and steam started coming from the radiator. I let it cool off and drove into the barn. It did not overheat when I just drove it around. I drained the coolant and flushed a tiny bit with some water and then filled it with coolant/water. I have checked the thermostat and found out that someone had already removed it! The radiator fins are fine and clean. I have filled it completely up with coolant and there is no air in the system. The temperature gauge is broken. I then took it out and tried plowing with it again to test it under load. This time it did not overheat at all. Some coolant came out of the overflow hole under the fill cap, but I have heard that is normal if you have filled it all the way up. The radiator hoses and the water pump got a little warm and you could tell that it was slowly warming up, but nowhere near overheating and it handled plowing fine. Can I assume the water pump is OK? Remember there is no thermostat. Should I install a thermostat and how important is it? How do I install a temperature gauge? It looks like I need to raise the fuel tank. How do I do that nd is there another way? What is the result of driving it without a thermostat? All advice and help is appreciated. It is very important to me to restore the tractor and have it working correctly. I also rely on it for my hobby agricultural production with plowing, harrowing, etc.

A diesel engine needs a thermostat to maintain and efficient operating temperature and get the best fuel mileage
from each gallon of fuel used. It will also keep the water circulation rate under control and many times prevent
cavitation of the coolant in the system which sometimes leads to ping holes in sleeves.

There is a chance that there is an overheating issue if someone prior to you has removed the thermostat. One tractor I now have used to have a serious overheating issue for a
previous owner, I can tell the signs of serious boiling etc. Once I took the engine apart I found the block was very seriously filled with sludge, so bad that around sleeve #4 there
was virtually no room for coolant circulation. I flushed the block thoroughly and it is perfectly fine now. I'm surprised plowing in 3rd low would make it overheat unless you have a
really hot summer day and the ground is very hard. Make sure your fan belt is tight enough that there is no slippage turning the water pump at full speed.

It is normal for a tractor to overheat if you try to pull too much of a load for too long. Also it is not unlikely that in the past it was run for a few months or years with just water and has some rust as Gene said. I have found some blocks with it pretty deep around the rear cylinder.

You need a thermostat (or racers use a proper sized washer)to slow the coolant down, otherwise it goes through the radiator to fast to cool properly.

Needs a 195F stat. Those that operate equipmemt without stats or rad shutters do not understand thermodynamics.