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Using relays

The key to making the electric fan(s) cycle on and off is to make sure the temp sender's "off" temperature is 10 degrees higher than the thermostat that you are using, otherwise the fans will run continuosly:thumbsup:
 
I put the sender in the water pump where a heater hose would normally go so I have a 180 deg. thermostat, and the sender is 170 deg. on, 160 deg. off. Keeps the 409 at 190 degrees. (But what's that got to do with relays you ask?)
 
So once your fans trigger they never turn off?
It is triggered by the water coming out of the radiator which will become cool enough to let the fan shut off.
 
I put the sender in the water pump where a heater hose would normally go so I have a 180 deg. thermostat, and the sender is 170 deg. on, 160 deg. off. Keeps the 409 at 190 degrees. (But what's that got to do with relays you ask?)
I think so too. The temperature to monitor is the radiator water exit temperature, which is of course the measure of the cooling effect. If the water exit temp exceeds a setpoint, means the radiator needs help so fan kicks in till the exit temp hits the low setpoint, then switches off.
Its a classic relay application because the temperature switch only switches relay coil current, and the relay contacts handle the fan motor current.
 
Hey Rooster, does your fan run all the time when the engine is up to operating temperature or does it cut in and out? Thats a neat way to hook the fan up.
It is on and off . I purchased a spal temp sensor at Parr in Oklahoma city
 

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