noisy coolant fan

[luy123]

I just got my cooling fan clutch replaced and when I drive (around 2000 rpm) it sounds like a jet engine. The fan never was that noisy even when it was new. Could they have put the wrong one in? Is there a way to tell how fast it should turn (or how much noise it should make a certain rpm)? '94 astro Thanks

[old_master]

Sounds like you have a bad fan clutch, here's why:

When the clutch is cold the fan should turn relatively hard, as the clutch warms up the fan turns more freely. When the ambient temperature is below 35 degrees F and the engine is cold, it's very easy to tell when the clutch warms up: when you start the engine, you will immediately hear a "roar" from the fan, as the clutch warms up, it engages and the "roar" is less noticeable. This “roar” sound comes and goes as the clutch and engine warm up. With sub zero ambient temperatures, and or a faulty thermostat in the engine, the clutch may take several minutes to engage, or may not engage at all. Fan clutch temperature is totally independent of engine temperature however if the clutch is disengaged it will cause the engine to run slightly cooler, and the fan will "roar". The purpose of the fan clutch is two fold: Reduce the “roar” and drag on the engine at normal operating temperatures, and also to provide air movement across the radiator when the engine is at lower rpm and or vehicle speed. When the engine has achieved normal operating temperature, air is drawn through the radiator, heated by the coolant and across the fan clutch. This warm air, along with heat generated inside the clutch itself by slipping, keeps the clutch engaged. If the engine is operated without coolant, eventually the engine will overheat and the warm air heated by the coolant from passing through the radiator obviously is not present, the fan clutch cools, the clutch disengages, the fan “roars” and attempts to cool the engine. (That is inherent with the design and actually does very little to prolong overheating.) Under normal circumstances and when all systems are operating properly, the fan clutch should be fully engaged by the time the engine reaches operating temperature. There are specifications for the fan clutch and precise ways of checking its operation, one of which utilizes a piece of reflective tape attached to the fan clutch and using a special tachometer with a built in strobe light, much like a timing light.