I have dual electric fans in my '87 V12, and have always wondered about at what speed they no longer are effective.

I've put together a fan tachometer, which I'm in the process of bench testing. The next step would be to mount it in the car, and log its various speeds, i.e. determine how fast the fans actually turns when voltage is applied, at what vehicle speed the fans turns at that same speed with no voltage applied, and the like. The idea is to shut power off to the fans when they are no longer helping cool things.

Before I go any further with this, has someone already done something similar. If so I can't find it, but thought it worth asking.

Thanks,
John
1987 XJ-S V12
70,000 miles

 

As a reference point, I have measured the air speed from a pair of 2006 Chrysler 300 fans on the bench connected to a battery and I got 41 km/h air speed. So presumably at a vehicle speed faster than 41 km/h there is more natural air flow than fans could provide, so no need for fans.

 

They say that car speeds faster than around 30 mph fans are no longer effective/needed. Say your electric fans come on @ coolant temp of 200F via a sensor located in the radiator & your speed is 65 mph, what if anything shuts the fans off @ this speed. The fans are also @ a higher speed with the AC on .

 

Isn't it easier to just setup a temp sensor as a switch?


Anyway, if the air is spinning the fans then wouldn't the load become negligible at higher speeds, so they don't consume much power anyway?
If it makes you feel any better, I replaced my aux fan with a $20 chinese fan about 6 years ago and its just set to run with the key on, so its on constantly and has had a decent service life so far.