A word to the fans

Engine fans are key to proper cooling. They work by pulling a tremendous amount of air over the fins in the radiator. Most engines today have a ring shroud which reduces the gap between the edge of the fan and the shroud. These shrouds are usually mounted on the engine, so that when the engine moves, the shroud travels with it. These systems are very efficient. Today’s fans on 15-liter engines at full RPM can pull up to 90 HP.

Make sure the fans are clean and maintained properly with no imperfections such as nicks, deformed blades, cracks, gouges, etc. A damaged fan can expel blades, through the radiator, shroud, hood, etc.

There are three common fan drives available.

• Air on/off is the most popular. It has clutch linings that can wear out, so it has to be monitored and maintained.

• Next is viscus which is not serviceable. It engages when the temperature of the radiator increases. This hub protects the fan belt since it’s a gradual engagement as opposed to a shock with the air On/Off.

• The 2-speed fan operates approximately half engine speed all the time, which could reduce fuel economy, but shortens full speed engagement. It is preferred in off road conditions, because full fan engagement stirs ground dirt making it difficult to see and drive. It too is good with fan belts since the shock is much less than if the fan were idle.

Some environments such as feed lots plug cooling systems on a regular basis. There are a couple manufacturers who build reversible fans which operate on a timer. They operate in a sucker mode, then reverse into a pusher mode to expel debris that has become suctioned to the front of the charge air, HVAC condenser, any other coolers in front of the radiator. They are not very efficient in either direction but do a nice job of removing contamination in this application. Engineering restricts the engine HP available with these fans due to the reduced cooling effect.

It’s all about tradeoffs.