I have a 1949 8n. I have rebuilt the entire tractor, new radiator, water pump block, etc... I completed the project in 1995. During the restoration I put a thermostat in the top radiator hose. About a week after I put the tractor back together, I apparantley warped the cylinder head and ended up with water in the oil pan...........I suspected a bad thermostat. After re-planing the head, I put it back together without the thermostat, and have run it regularly for the las 6 years with no problems.
The location of the thermostat (in the upper radiator hose) makes me think that unless the block gets pretty hot, it won't open. A better design came along with the Jubilees, where it is located on the block, and would warm up along with the engine. Has anyone had this problem before, and do I dare attempt to put another stat in the hose????????????