hi everybody! i just got done install a 4 core aluminum radiator, new pump (oem), 192 degree heavy duty stat, new hoses, & heater core. plus a flush. i have the electric fan switch sensor hooked up to the top radiator hose. currently i have the switch to come on at 200 degrees and it cools down 6 degrees before shutting off. does that sound right? or should i lower to 196 so it shuts off at 190, 2 degrees lower that the stat trip point. AND to add to it, do i even have the switch sensor in the right place? i heard some guys running them on the bottom radiator hose.

 

Part of the idea of a electric fan is less load on the vehicle, especially when you are running down the road. There is a decent load on the alternator when the electric fan is running. So you do not want the fan to run all the time, only when it's needed. If you get the fan switch temp too close to the thermostat temp, the fan will run all the time and defeat a large part of it's purpose.

So experiment with it, when you are running down the road at speed, there is enough air going through the radiator, you do not need the fan, it should be off. Once you pull up to a stoplight, it needs to sit there a little bit, the temp will rise up and the fan will come on. As you pull away and there is airflow from moving again, the fan should eventually cut off again. Give this stuff a little lee-way as far as setpoints. There is a deadband made into the switch, so the fan or whatever it controls does not cycle on and off quickly. So you might set it for 205, it might not come on till 210, and turn off at 200.

Caution; If you have A/C and it works, make sure you wire the A/C compressor circuit into your fan controls. If you have the A/C on, the fan will have to run 100% of the time so the A/C system works properly. I forgot this on one I did a few years back and there was a loud bang under the hood, the high pressure pop-off on the A/C compressor went off because the electric fan was not running yet (engine was cold) but I had the A/C on. Lesson learned on that one.

 

A modern vehicle wants to operate over 160 and is most efficient between 175 to 225. Optimal is between 185 - 215.


An OEM F-150 thermostat is fully open at 192. Maybe 10 or 20 degrees before that actually happens, the thermostat is already slowly opening to allow coolant to begin circulating. Keep in mind that the thermostat stays open, and does not close until the temperature drops by about 20 degrees.

Thermal fan clutches typically engage around 205. 205 degrees of air temperature around the fan clutch is not going to be the same as what the cylinder head sensor reads, or what a probe in the radiator fins will sense. The temperature of the transmission has no input on engaging a mechanical fan. Modern cars have computers which turn the fan on in stages of low speed, medium speed, high speed, etc. The fan turns on with an algorithm using different sensors like the cylinder head sensor, coolant temp sensor, transmission fluid temperature sensor, etc, along with other operational inputs like HVAC activation. With a good scan tool, you can usually see data regarding fan speed. On my 2016 Ford Transit Connect, the PID displays FANDC %. Aftermarket fan controllers can be fixed at 180, 190, or adjustable from 150 - 240.

Most cars are designed so that when the car is in motion, the CFM of the airflow coming through the grill is enough to maintain the operating temperature at a safe level - if the thermostat and water pump are operating properly.

My F-150 is an 11th generation which came with a mechanical fan, and now has an aftermarket fan system. I have observed that with the factory 192 thermostat, the cylinder head sensor will infer that coolant temperature reaches up to 195 - 200 before the temperatures quickly drop. What is happening here is that when the thermostat fully opens, the temperature continues to climb where the sensor is reading the temperature. The coolant now has to travel through the upper hose, into the radiator, dissipate heat, and return much cooler fluid back via the lower hose. Within a few minutes, the temp will drop to 175 - 180. All of this is able to happen without the fan turning on at all.

My aftermarket electric fan system has 2 fans, with the first fan set to turn on at 200, and the second fan to turn on at 210. The only time that the fan turns on is in stop and go traffic. Anytime the truck is traveling more than 20 miles per hour, there is sufficient airflow to cool the fluid circulating through the radiator.


If you are very concerned about overheating, there are thermostats which open at lower temps. I have used them. On my 5.0, I had a 160 thermostat. The engine still got to operating temperature and was able to maintain operating temperature. With the thermostat opening at a lower temperature, it just took longer to reach operating temperature. When the thermostat opens at 160, there is an initial drop of maybe 5 degrees, then the engine temperature will still rise to operating temperature. It did not "overcool" the engine. You won't have to worry about having a 160 thermostat and your engine not getting warmer than 150. I had a fan controller set for activation at 180. The fan controller used a temperature probe in the radiator fins. By the time the radiator fins reached 180, the cylinder head temperature was usually around 190.


As for your electric fan, is this an aftermarket kit with an adjustable controller? What are you using to read the temperature with? Are you using a hand held, point n shoot thermometer? Or are you reading the cylinder and coolant temperature from the OBD II with a scan tool? I would suggest a scan tool with a large display, a very long cord, or BlueTooth technology, so that you can read it while you're standing in front of the truck with the hood open. In my 2007 truck, I have a ScanGauge II. In my 2016 van, I am using a tablet computer.






What you will find with a scan tool and a thermometer, is that when the cylinder head temperature sensor shows 190 - 195, you will actually hear the thermostat "click" or "pop" open. Your thermometer will show that the engine is hotter than the hose, and that the hose will be hotter than the radiator fins. The fluid could exit the engine at close to 200 degrees, and the thermometer at the radiator fins could easily be 10 degrees less. The temperature of the radiator fins around the lower return hose, and the lower return hose itself, could be significantly lower, by 20 - 30 degrees.


Most manufacturers of aftermarket fans suggest that you insert the temperature probe in the radiator fins either under or next to the upper radiator hose.


THERMOSTAT PROBE INSTALLATION Placement: For best results we recommend installing the probe as close as possible to the water inlet of the radiator.









What you are trying to accomplish is turning on the fans when the cylinder head is around 200. This is why there are fan controllers with temperature probes set at 180 and 190. Do not place the probe sensor next to the lower radiator line, which is the return line. If the temperature at the lower return hose is 200 degrees, then you have a problem, because the coolant is probably 225 - 250, or more, at the cylinder head.