skipmarcy said:
Monte & Catman are both correct. Alot of uneducated people will remove a thermostat trying to fix a overheating problem and just cause themselves more grief. To clarify why an engine would actually overheat with a thermostat removed - at higher operating RPMs the water pump is circulating the coolant too fast for proper heat transfer, first the heat from the engine to the coolant, then the heat from the coolant to the radiator cores, it's not staying there long enough for the heat transfer to occur. Now if you have a radiator that's half clogged it might cut the flow enough to fool you into believing you've "fixed" the problem by removing the thermostat, but all you've done is mask the real rpoblem and it's going to bite you in the...
I've never heard of overheating because the thermostat was removed... and i doubt if removing the thermostat makes that much difference in flow restriction, as the coolant liquid finds its way through narrow holes and galleys in the cylinder heads and around the walls.
My brother once bought a Nissan Patrol 2.8 turbo diesel jeep. The engine didnt came to operating temperature on chilly days so we assumed the thermostat was stuck in open position.
When the guy he bought it from, sent a thermostat by mail, we opened the thermostat housing and found.... just an empty housing. when we put in the thermostat, it overheated every small trip.
The cause of this, is loss of compression by leaks, mostly through the valves, or by the piston rings.
About flow, i had a cooling problem on the Zetor 5245. It overheated quickly even though the previous owner replaced the original fan for a BMW automobile fan, to get some extra wind draft.
After asking around, i found that some models came with a fine mazed radiator: it had the double amount of pipes, with half the diameter.
Both water flow THROUGH the pipes, and air flow AROUND the pipes were too much restricted. I replaced it with a coarse mazed radiator of a wrecker, a 5718 of early 70's. I also polished the valves and valve seats, which were pitted because of earlier overheating.
I also turned open the fuel pump a turn or 2, and with the extra power i have a much smoother tractor that hasnt gone over 105ーC again in the hottest summer days.
About the need of a thermostat, as mentioned by others, the engine has to get to a reasonable exhaust gas temperature to prevent carbon build up, and to vaporise condensates of fuel and water in the oil.