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I've been pondering this for some time and want some comments on it. My thought is to install the fan switch on the cooler side of the radiator or lower hose going to the water pump. After all, shouldn't the fan be on or off depending on the temp of the coolant returning to the engine? Seems like this would be more accurate than using the radiator inlet temp to control the fan. With an efficient enough radiator, the thermostat would set the minimum engine temp, and if travelling at road speed, there should be enough air flow to keep the coolant temp down low enough that the fan would not need to come on. At low speeds or stopped in traffic, the coolant returning to the engine would increase in temp due to less air flow and turn on the fan, to cool it. I would think a lower temp switch would need to be used vs the one normally used in the head or thermostat housing. So if I am using a 180 deg thermostat, would a 170 deg switch be good? Give me your thoughts pro or con. It won't be any more or less wiring than the conventional way, just sensing the coolant temp returning from the radiator.
I bet I could put the sensing bulb inside the lower hose and then slide it onto the water pump with a good clamp, it shouldn't leak. I just hate to put a probe into the fins on a new radiator.
That's the same one I am using and I also put it in the radiator hose. I put it in the upper hose but since it's adjustable it shouldn't matter where you put it because you can tune it to come on at a stop light and off once you get going again.
I installed a PWM fan controller last year from Derale and the temp sensor is installed on the output side of the radiator. Originally it was s probe installed through the fins but as it turned out the aluminum rads were causing issues and they switched to a surface mount probe, again installed beside the out side of the rad
BTW, didn't get a ton of road time but the system works fantastic
M
I wouldn't recommend it. By the time your lower hose would heat up enough to turn on the fan your actual engine e temp would be high. They put a sensor/switch in the outlet to react to current engine temp, not coolant out of the radiator temp.
This is an interesting topic. Cooler side of the radiator may give you more consistent coolant temp going into the motor, but is that what's really needed? in order to maintain the same engine temperature under varying loads, the engine may need cooler or warmer coolant temps coming from the radiator. So I vote against the sensor at the cooler side of the radiator.
The thing I like about the PWM controllers is the fan doesn't snap on at a preset temp, it gradually spools up as the temp rises. So let say you want full on fan at 190 degrees, the controller may actually start the fan running slowly at 175, and as the temps creep up, the fan spins faster until full on at 190 degrees. Chances are the coolant gets enough fan speed well before it actually needs to run full fan, and of course as the car begins moving forward, the airspeed through the radiator will out flow the fan anyway.
If you want the fan to turn ON when the engine is getting too hot, measure the temp at the coolant outlet for the engine and can switch on as soon as it is needed.
Can you do it the other way? Sure. But you would need to know what the radiator's exit temp is when the engine outlet is getting too warm. Hmmm... why bother? Just install it where it should be.
Ok, most are opposed to the idea. Thanks for the comments. I'll reply to this thread after I get it installed and give some info on how it works out, good or bad. Probably some time in the spring, this is on my winter list of things to do.
Coolant temp switch for fan
