Cooling fan on/off
 

I want to put the radiator fan on an override switch that will allow me to run it on cammand or leave it in stock configuration. It also needs to be stealthy enough and easily reversible for Cali smog inspections.

For power to run the fan, is there any risk to tapping the power supply line for a heated O2 sensor? The connector is really close to the radiator and whenever the car is on, the O2 gets power. It's not the signal line. Just the power line. But would it mess up the O2 functions?

I'm not sure if the O2 sensor heater circuit can handle the amp draw of the fan. If your car has a dedicated temperature switch for the fan, I'd just add the override switch in parallel with that. Either way, I'd be trying to activate the cooling fan relay, not the fan itself. Why do you want to override the fan control?

I agree, I'm not sure that'll be able to supply enough amperage.

Thanks guys. I want to switch it because I find it to be a bit lazy when there are spikes above 200*F. I also think it could be an FE strategy to switch it on during DFCO runs. A long DFCO will dramatically lower coolant temps. But short DFCO runs have little effect. If I could turn on the fan, I would get "free" cooling. I say free because I grid charge my deep cycle battery and mainly run the alternator during DFCO.

I was thinking of disabling the fan and spraying water on the radiator. A sprayer motor should uae less energy than a fan motor.

Hahaha! That would be a bad idea. I think you'd surely ruin your engine in short order.

Why is that. It gets water whenever it rains.

A hypermiler's radiator fan should never run.

Only time mine run is in the middle of summer with a full grill block - even then only really if towing. In normal driving the thermostats rarely even open fully.

I don't even have a fan. :)

My engine has a water jacket on the exhaust manifold to recover extra heat and aid in warmup. While moving on level ground it doesn't come on, sure. But, Vermont is a mountainous state. Even if my radiator fan doesn't come on 95% of the time, I still want to have it for that other 5%.