Thermostat: Description and Operation

PURPOSE
A pellet-type thermostat controls the operating temperature of the engine by controlling the amount of coolant flow to the radiator.

OPERATION
On all engines the thermostat is closed below 195�F (90�C). Above this temperature, coolant is allowed to flow to the radiator. This provides quick engine warm up and overall temperature control.

GENERAL INFORMATION
An arrow, plus the word UP is stamped on the front flange next to the air bleed. The words TO RAD are stamped on one arm of the thermostat. They indicate the proper installed position. The same thermostat is used for winter and summer seasons. An engine should not be operated without a thermostat, except for servicing or testing. Operating without a thermostat causes other problems. These are: longer engine warm-up time, unreliable warm-up performance, increased exhaust emissions and crankcase condensation. This condensation can result in sludge formation.

CAUTION: Do not operate an engine without a thermostat, except for servicing or testing.

FAILURE
The more common type of thermostat failure, usually found on high mileage vehicles, is a thermostat failed in the shut position. The temperature gauge (if equipped) will give an indication of this condition. Depending upon length of time that vehicle is operated, pressure cap may vent. This will expel steam and coolant to coolant reserve/overflow tank and to surface below vehicle.