Since my stock ECU no longer activates the fan on my '99, I'm going to install a thermoswitch.

I'm getting an aluminium radiator which has a bung for a thermoswitch, but I'm not sure at what to activate.
I guess at a lower temp than oem because the rad will be cooler than the stock location, but how much.
Anyone ever measure?

 

I think a better option would be to put it in the heater line going from the block to the heater. You could cut the hose and put a pipe in between with a bung for the thermistor. That way, you wouldn't have to guess the temperature.

 

stock 99 switches at 210-215*F IIRC. something like that. I always trigger at 200*F

 

BMW sense radiator outlet temp to decide to turn the fan on, which is logical.

I would set it to 5*C above your t-stat opening temp.

 

I'd make it lots and lots lower than that.

 

Ordered a 85-75°C switch and will go from there. Will do some logging in TS to see if it's right.