Viscous Fan Clutch
 

Mechanic pointed out that my fan is always engaged on my 300SEL 89. Fan clutch is bad. The car does not run any cooler but normal operating temperature. Apart from a little howling when I accelarate hard is there any down side to this.

Sandeep

Shouldn't cause too much of a problem, but will definately slow up the warmup process in the winter.

Thirty years ago most cars had fixed engine driven fans. Warmup is controlled by the coolant thermostat, not the fan.

Bottom line is that there is no ill-effect, other than more engine noise and a slight loss of fuel economy that you may not even notice unless you track fuel mileage very carefully.

Duke

Thanks for the info guys. Is there any relationship to the clutch being engaged all the time and the tightening of the centre allen bolt. Meaning overtightening can cause this.


Sandeep

No, but you REALLY don't want to overtighten the center bolt. It is very easy to strip, and very hard to remove once that happens. 45 Nm is the proper torque spec, I believe.

Warmup is controlled by BOTH, the thermostat and the fan. The thermostat doing the job of controlling the amount of coolant flow, and the fan controlling the temp drop of the coolant. A fan running 1:1 when cold will delay the warmup cycle. Also, what would be the purpose of designing a viscous-clutch setup if it had no effect on cooling performance? Perhaps the worst result would be a delay in cabin heat. The cooling system (obviously ) is designed for each car. For example, simply chucking a viscous fan setup for an electric fan can be a challenge because of the hysteresis of the electric sensors and create higher than desired stress in aluminum engines. Also,

When the engine is cold the themostat is closed, which forces outlet coolant back into the engine through one or more bypass circuits without going through the radiator. After a cold start the coolant in the radiator basically sits there without circulating, and it will remain near ambient temperature regardless of air flow or lack of air flow through the radiator.

Once the themostat begins to open, coolant flows into the radiator forcing the cold and cooled coolant into the engine. The thermostat doesn't control coolant flow through the engine. It controls coolant flow through the RADIATOR!

Fans are needed primarily at no or low road speed. A fan clutch allows the use of a large fan that flows lots of air at idle and low revs without excess noise or parasitic power loss at high revs.

Duke