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The job of an automotive thermostat switch is critical. Some folks call them engine coolant temperature sensors, some call them ECT sensors, some say "coolant temp sensor", but no matter the name, they all perform a similar function. Thermostat switches take readings of the coolant temperature sensor and they control the function of vital components such as electrical cooling fans, temperature gauges and can even control some components and fans in the air conditioning system.

We’re going to talk about the most common type of thermostat switch used in a typical hot rod, street rod or street machine, which is an open/closed automatic temperature switch aka thermostat switch. These are primarily used to control electrical cooling fans. An ECT sensor is very, very simple. It generally is screwed into the engine’s cooling system via pipe threads and it has a probe that gets exposed to water. When the water is cold or below the switch’s specified temperature, it will stay in the “open” position. Once the engine’s coolant gets up to a certain temperature (usually 185-210 degrees F), the switch will “close” and it will cause the ground connection it makes with the engine through it’s threaded body to be internally connected to it’s sensor wire terminal, which in turn connects to a relay. When this happens, the relay energizes and sends voltage to the radiator cooling fan and turns it on automatically. So, in this type of switch, it merely grounds out the relay when the engine reaches the right temperature. When the engine cools below that temperature, the ground is switched off.

Of course there are many, many styles and types of thermostat switches available. There are simple on/off switches, or you can get a handy, prewired thermostat switch/fan controller kit that has the thermostat switch, a ready-made wiring harness and a relay. There are all-in-one kits like the units marketed by Speedway Motors, Spal USA, AFCO, Dewitt’s or Flex-A-Lite just to name a few.

If you want a little more control over your radiator, engine oil or transmission cooler fan, Speedway Motors offers thermostat switches that you can set the EXACT temperature the fan will turn on and off. Want more than that? How about a programmable PWM or fan pulse width modulator? These types of thermostat switches can actually control the fan speed instead of simply turning it on and off. Speedway Motors offers thermostat switches that can even control multiple fans and are programmable like the unit we carry from Dakota Digital, Intellitronix or Flex-A-Lite.

Many of our thermostat switches don’t use engine coolant temperature switches at all. There are some styles we offer such as Speedway Motors part # 91604041, that uses a simple probe that gets inserted into the radiator’s cooling fins to monitor temperature. Heck, we even offer some that use the engine’s temperature gauge to control the fan.

Don’t blow your cool, man! Shop below to find the thermostat switch, fan relay kit, pulse width modulator, coolant temperature sensor or fan controller that is right for you! Shop Speedway Motors!