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L20b electric fan setpoint


620crumudgeon

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I've replaced the L20b's mechanical drive fan on my '76 620 with an electric cooling fan. The turn on temperature set point is adjustable and I need to know the temperature at which the fan should turn on and the maximum water temperature. I will be inserting a temperature probe between the radiator cooling fins connected to a cooking temperature gauge that's accurate to 1 degree F.

 

Should the fan tern off temperature be less that the thermostat temperature rating? The thermostat is a 180 degree thermostat.

 

John

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One of the later Nissan FWD cars had a short length of pipe with a sensor that was spliced into the lower rad return line. It samples the coolant temperature coming out of the rad. This is the best place for this. All I did was slice the rad hose and insert in pipe with hose clamps. Ran the wires to a relay with power through a fuse from the positive battery post. This way the fans can come on after the car is shut off when it heat soaks.

 

I don't think a cooking thermometer is going to read the actual coolant temperature only the air blowing through the rad, which is going to vary during the year. 

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The temperature sensor for the fan controller is in the thermostat housing where it can read the water's temperature. The cooking thermometer is used to read the temperature of the water flowing through the radiator. The probe tip is between two cooling passages near the radiator inlet.

 

The three temperatures I'm interested in are: 1) the fan turn on temp; 2) fan turn off temp; and 3) maximum permissible water temperature. The fan turn on temp should be below the maximum permissible water temp to provide a margin of error.

 

John 

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These parameters depend a lot on radiator efficiency and fan CFM. Fan size and shroud type will also factor into the mix.

 

Modern electronic fans are often turned on at 205 F and off at around 195 F. For an old car, which runs at about 180 F, I would have them set to cycle on at roughly the same temp that the thermostat opens, then turn off at 10-15 degrees below that.

 

I just finished a CJ5 resto-mod project and I used a pusher fan (because of space constraints). I have it set to turn on at the lowest setting in the allowable range, which is about 140 F. It basically runs the fan all the time. I am only doing this while I work the bugs out, but will gradually increase it until I find the comfort zone. You could also try this method until you find a range that you are comfortable with.

 

So, are you using a pusher or puller? Are you using a full shroud or just the one built into the fan? Does the fan cover a majority of the core, or only half, or what? I think these are important to the equation.

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