engine fan question

Cruize · #1 12-07-2006, 01:25 PM

Why does the engine fan start when I start my Blazer? With the engine off, I can spin the fan blade freely, so I know the fan clutch is not seized up. Is it supposed to spin immediately upon start up?

ZL1power69 · #2 12-07-2006, 03:37 PM

the factory fan is a traditional mechanical fan that is connected to the water pump. if the engine is running the fan will spin. when the engine warms up the fan clutch engages and the fan noise stops.

Cruize · #3 12-07-2006, 07:49 PM

So are you saying the fan noise is generated by the fan NOT spinning and the noise goes away when the clutch locks up and starts spinning the fan?

Over the summer, I noticed that the fan started spinning as soon as I started the engine, even though it was cold.

ZL1power69 · #4 12-07-2006, 08:38 PM

Quote:

Originally Posted by Cruize

So are you saying the fan noise is generated by the fan NOT spinning and the noise goes away when the clutch locks up and starts spinning the fan?

Over the summer, I noticed that the fan started spinning as soon as I started the engine, even though it was cold.

no the fan is always spinning, even when the engine is stone cold. just that when the engine is cold, the fan clutch is disengaged and the fan makes that roaring sound. when the engine warms up a bit, the fan clutch engages and the roar goes away, but the fan continues to spin.

Cruize · #5 12-08-2006, 02:52 PM

The Blazer (I only put about 4k miles on it since I bought it 18 months ago) is my first vehicle with a mechanical fan, my other car has the engine sitting sideways with an electric fan.

After discussing this fan question with my brother last night, it's logical (at least to me) that there's not enough slippage in the clutch to completely prevent the fan from turning at all, which is why it spins on a stone cold engine. So it's pulling a small amount of air across the engine. But then once it gets hot enough, the clutch locks up and the fan is spinning at a much higher rate, pulling a whole lot more cooling air.

Thanks for the help.

DelCoch · #6 12-09-2006, 06:51 AM

I believe you all got it backwards. When you hear the roar, the clutch is locked up with the fan, giving max airflow through the radiator. In the summer on a 100+ day, you will hear the fan kick in and roar when sitting in rush hour traffic. The roar is the result of the fan pulling max amount of air.

The reason it roars when you first start it up is; when the vehicle sits for a few hours the oil in the clutch will settle to the bottom of the fan clutch, thus it will be locked up until the oil is evenly distributed around the clutch, which usually only takes about 2-3 minutes. The clutch then lets the fan free wheel until such time that enough heat builds up to expand the bands inside the clutch causing it to lock up again. It works something like a thermostat.

If you replace your fan clutch, the instructions that come with the new fan clutch will explain this.

BlazerLT · #7 12-09-2006, 06:03 PM

I just underwent a fan clutch replacement here.

http://www.automotiveforums.com/vbul...d.php?t=650434

The fan will engage when cold and will disengage when you start driving and put the rpms over 2300rpms. Then it won't come on again until you shut it off and it is cold OR if you get above 195f when it is supposed to lock up more and spin faster.

Mine was not howling at the start and this was because it was weak and defective.

The fan clutch is not mechanical, it is controll by a viscous silicone fluid moving which engages or disengages the fan.

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