Original submission by T Mar 9th 2007:
Back to Cooling
Submitted by T on Fri, 09/03/2007 - 09:21.
If the fan is too far back it won't cool at idle. If the fan is too far forward it guzzles horsepower when the revs come up.
Rule of thumb, make sure that the fan is throwing back hot air at idle. If it's too far back it won't. If it's too far forward the fan will growl when the revs come up meaning that it's too close and wasting horsepower by breaking up the airflow where it leaves the radiator.
I fitted longer bolts and spacers between the fan and the Eaton hub to move the fan back. It reduced the load on the engine while still moving adequate air. (See the lower half of Ruski's image).
===Thermo (Electric) Fans:=== I favour placing these in front of the Radiator for these reasons:
1. The Electric Motors stay cooler because they live in the cold side of the airstream.
2. Thermosetting Plastics shrink when they heat up. Constant heating makes them crack. If you aren't sure what your fans are made from then the front of the Radiator is a good place to mount them.
3. Air Dam. Should the fans generate more air than the Radiator can allow past, a pressure
zone will be formed in front of the Radiator ensuring good exposure of the Radiator to the airflow.
If the fans are fitted behind the Radiator and a vacuum is formed it's a negative because vacuums don't support heat transfer.
See also Fan_Braking for efficient Thermo Fan usage.
===Shrouds:===Fitting the Fan Blade so that it is half in the Shroud and Half out provides good efficiency.