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I need to buy a thermostat switch to turn on and off my electric fan on my Big Block Chevy, The two switches they offer are: On-186 Off at 161 Or On at 200 and off at 186. I will be also running a air conditioner. What one should i get?? :confused:

Personally I would prefer the cooler one, but I live in the desert, so Heat is a big factor here.

I would like to add some advice if I may. Regardless of which one you get, splice into the wire that goes to the sensor, and run it to a seperate toggle switch. Ground the other side of the toggle switch. This will give you independent control of the fan, allowing you to turn it on sooner if you feel the need. This weill not interfee with the normal operation of the sensor. (The sensor is merly a temp. sensative ground. All you are doing is adding a second, switched ground) Also. Be sure to use a relay rated at least 30 amps for safety. Dont want any electrical fires!

Curly has some good advice !! It also works best if the electric thermostat is mounted in the engine block (intake manifold) and not the radiator core. The engine block thermostats do cost a little more, but they are also much more accurate. After all your concern is the engine block temperature. Best example is having a thermostat stick shut, (and these new "economy" thermostats do it more often than the old ones) the electric fan will not come on, but you engine block will be sweatin like crazy....Randy

What year big block? What was the normal (factory) operating temp for that engine?

I think it a 1970 402,I dont know what the operating temp was for that motor........

That motor takes a 180 degree thermostat, so if you put the hotter sensor on it, your fan will probably run all the time, because the engine won't be cooled down enough to close the thermostat.

If you put the lower temp sensor, it will only run when the thermostat is open, which means the engine *needs to be cooled. Therefore I'd choose the On at 186 - Off at 161 sensor.

Thanks guys for the info, I ordered the cooler senso r

sorry I didn't see this sooner, but did you think about how the fan will always be running if you have a 180 stat and a fan that won't shut off until temp drops to 161. I really don't see a need for the fan unless the temp reaches 200. Also there are adjustable temp fan controls which let you decide when it comes on