The sensor is on the engine but on the water flow not the oil. Apparently no engine, car or tractor has it on the oil system. Problem is that when there is NO WATER in the system, the sensor does not pick up the heat as efficiently, thereby allowing it to overheat substantially before any signs are shown. Perfect storm situation - Water leaks out while engine is not running, no sign of it unless you are lucky enough to have it parked where it can be seen, but not on dirt or rocks. Then you check the coolant reservoir, it is fine beach the siphon does not work when below the pick up point. Then the heat indicator does not go up because it has no water flowing past sensor. Then you are running along all fine and KABOOOOM, engine locks up. From the User Manual "BChecking Coolant Level
To avoid personal injury:
A Do not remove radiator cap while coolant is hot. When cool, slowly rotate cap to the first stop and allow sufficient time for excess pressure to escape before removing the cap completely.
1. Check to see that the coolant level is between the "FULL" and "LOW" marks of recovery tank.
2. When the coolant level drops due to evaporation, add soft water only up to the full level. In case of leakage, add anti-freeze and soft water in the specified mixing ratio up to the full level. (See "Flushing Cooling System and Changing Coolant" in "EVERY 2 YEARS" in "PERIODIC SERVICE" section.)
3. When the coolant level is lower than "LOW" mark of recovery tank, remove the radiator cap and check to see that the coolant level is just below the port. If level is low, add coolant."