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esisson · 05-09-2008, 03:20 AM

Found this on the net this morning. Tells me what I wanted to know.

A fixed fan delays and slows engine warm-up because it's pulling cold air over the engine and radiator as the engine is still not up to temperature and in reality, needs no cooling yet.
A fixed fan also makes lots of noise. Especially when driving on the highway, it tends to beat at the air instead of adjust to any differences.
A fixed fan has no ability to "give" under sudden acceleration or to not "engage" when not needed. Your engine does not always need to have additional cooling - cool nights, cruising down the highway at part throttle and various other situations don't really require the fan to be engaged and spinning 100% of the time. The added drag of having to spin the fan when not needed takes horsepower away that could be used to push the car forward just to thrash at the air.
Converting to a clutch fan addresses each of these points with a very simple and well-proven device - the 100% mechanical thermostatic clutch unit that mounts between the water pump and the fan.

The thermostatic portion allows faster warm-ups and better cold drivability as a result. The clutch allows the fan to "freewheel" (not spin at engine speed) until the engine is up to temperature and the fan is really needed. This means less airflow through the radiator and faster warm-up times. A small bimetallic spring similar to the one in a choke coil is mounted on the front of the clutch where it is exposed to heat from the radiator. When it gets hot enough, it "locks up" the clutch and the fan spins at engine speed to provide full cooling. When it cools off enough, it "unlocks" and allows the fan to "freewheel" once again.
The clutch portion allows the fan to be quieter because it can "freewheel" and adjust it's speed to match that of the incoming airflow through the radiator. It also does this at idle so that the fan, although it is spinning, is spinning at a greatly reduced speed compared to a fixed fan, thus making much less noise.
The clutch portion allow the fan to "give" in cases of sudden acceleration (so it accelerates more slowly) and the thermostatic portion allows the fan to "freewheel" when not needed. This allows a large amount of "freewheeling" at higher engine speeds such as when you are out on the highway and the fan really isn't needed, and the thermostatic portion allows the clutch to freewheel unless the engine is above a certain temperature and the fan is not needed right now because the engine is not warm or is not warm enough to need more airflow through the radiator.
A Word About Electric Fans...

05-09-2008, 03:20 AM	#2 (permalink)
esisson Member Join Date: Nov 2006 Posts: 33	Found the answers to my questions Found this on the net this morning. Tells me what I wanted to know. A fixed fan delays and slows engine warm-up because it's pulling cold air over the engine and radiator as the engine is still not up to temperature and in reality, needs no cooling yet. A fixed fan also makes lots of noise. Especially when driving on the highway, it tends to beat at the air instead of adjust to any differences. A fixed fan has no ability to "give" under sudden acceleration or to not "engage" when not needed. Your engine does not always need to have additional cooling - cool nights, cruising down the highway at part throttle and various other situations don't really require the fan to be engaged and spinning 100% of the time. The added drag of having to spin the fan when not needed takes horsepower away that could be used to push the car forward just to thrash at the air. Converting to a clutch fan addresses each of these points with a very simple and well-proven device - the 100% mechanical thermostatic clutch unit that mounts between the water pump and the fan. The thermostatic portion allows faster warm-ups and better cold drivability as a result. The clutch allows the fan to "freewheel" (not spin at engine speed) until the engine is up to temperature and the fan is really needed. This means less airflow through the radiator and faster warm-up times. A small bimetallic spring similar to the one in a choke coil is mounted on the front of the clutch where it is exposed to heat from the radiator. When it gets hot enough, it "locks up" the clutch and the fan spins at engine speed to provide full cooling. When it cools off enough, it "unlocks" and allows the fan to "freewheel" once again. The clutch portion allows the fan to be quieter because it can "freewheel" and adjust it's speed to match that of the incoming airflow through the radiator. It also does this at idle so that the fan, although it is spinning, is spinning at a greatly reduced speed compared to a fixed fan, thus making much less noise. The clutch portion allow the fan to "give" in cases of sudden acceleration (so it accelerates more slowly) and the thermostatic portion allows the fan to "freewheel" when not needed. This allows a large amount of "freewheeling" at higher engine speeds such as when you are out on the highway and the fan really isn't needed, and the thermostatic portion allows the clutch to freewheel unless the engine is above a certain temperature and the fan is not needed right now because the engine is not warm or is not warm enough to need more airflow through the radiator. A Word About Electric Fans...