Fan question
 

I have no idea if this has been covered in some long lost thread or even brought it up myself and just don't remember, but I'm being lazy today and not searching (and actually have no idea why it popped into my head right now) :D

Anyway, I was walking around in a parking lot a while back and noticed on a Saab or BMW or something that the radiator fan was mounted on the front side of the rad vs facing the engine. This got me thinking about all the time I spent in computer modding and when doing chip cooling it's more efficient to push air through the heat sinks than pull it out.

Would this concept apply to automotive cooling as well? Would it be more efficient (fan stays on for a shorter amount of time) to have the fan blowing air through the rad instead of pulling air through it?

It is about 50/50. Mainly depending on the ability of the fan to maintain a certain static pressure and on which side of the fan this pressure is designed to hold. Depending on the turbulence created by the fan blades pushing though fins could be less efficient. On the other hand turbulence and pressure drops created by the fins makes the fan less efficient when pulling.

Edit:
Similar argument regarding computer cases. Do you pressurize the case with intake fans or create a negative pressure case with exhaust fans. Both seem to work as long as the air flow passes by and through the CPU heatsink which is the thing that matters.

Unless you are stopped, putting another obstruction(the fan) in front of the radiator for air to go around isn't going to help.

There's also the dead air space right behind the fan's motor. Unless you build a proper shroud and mount the fans several inches from the surface of the radiator, you'll still be faced with dead spots.

The ideal setup is to have a single, large, speed modulated electric fan mounted behind the radiator, with a shroud completely sealed to the core, and flaps that open when the incoming air speed exceeds the fans capacity. Packaging constraints prevent this kind of setup on most vehicles due to the large plenum needed.

The fans you saw are auxiliary, not main, fans. They turn on for additional cooling and when the A/C is on.

The main fan is always behind the radiator. Having the main fan behind the radiator is more efficient and allows for a shroud with bypass flaps for higher-airflow operation on the highway.

Go to aftermarket fan sites (i.e. SPAL) and you'll see that pusher fans are rated less than puller fans.

Ok, that definitely clears things up. With chip cooling, dead spots were dealt with by using spacers, but the incoming airflow from moving wasn't really a concern :)

(as far as case cooling, I was always a fan of positive pressure for dust reduction)

maybe the fan was used as a generator instead of a fan. nt
 

.