by Bill Carberry, Cap-A-Radiator

The primary function of a thermostat is to maintain a minimum operating temperature in your car’s engine. When you start your engine cold, the anti-freeze/coolant mixture is kept within the engine by the thermostat. The coolant does circulate within the engine through the bypass hose or passage to prevent hot spots. When the coolant temperature reaches the specified opening point of the thermostat, it opens. Coolant will then flow through the radiator to keep the engine at a temperature close to the rated temperature of the thermostat. It is normal to see some fluctuation in the temperature gauge until the coolant temperature stabilizes. Just prior to the thermostat opening the coolant in the engine is at 180 degrees if you have a 180 thermostat. The coolant in the radiator is at ambient temperature. As the thermostat opens the hot coolant in the engine goes into the radiator and the cool or cold coolant in the radiator is drawn into the engine by the water pump. The thermostat is hit with this cooler antifreeze and closes down until it gets back up to temperature.

Most of today’s cars and trucks with computers and fuel injection are designed to operate with a 195-degree thermostat. If a lower temperature thermostat has been installed, it will affect several systems in your car. A vehicle with a computer-controlled fuel injection will sense the lower temperature and compensate by making the engine run richer, causing excessive fuel consumption and possibly a high idle. A lower temperature thermostat will also decrease the amount of heat available to keep you warm and defrost your windshield. Most older cars were designed to operate with a 180-degree thermostat. Changing to a 195 in the winter for more heat or a 160 in the summer to keep the engine cooler will not cause a problem on an older car but it would on a computer controlled car.

Many people think that putting a lower temperature thermostat in their car will solve a running hot problem. In some cases it may but in most cases it will only prolong the inevitable. The coolant will begin to flow through the radiator at a lower temperature but if everything else is not working properly your engine will still get too hot. You need to be sure that you have an adequately sized radiator, that it has a good flow through its internal passages, good airflow through the fins and a good cooling fan set-up.

If your engine has overheated badly due to some other reason, a previously good thermostat may go bad. The internal wax pellet may not open the thermostat the next time it reaches normal operating temperature. A thermostat can last many years but it might be a good idea to replace it the next time your cooling system is being serviced as a preventative maintenance procedure.