Cold weather fan operation

[hey-you]

Hi,

I'm trying to understand here, and while I've found similar posts, if I could get confirmation that I've actually understood them that would be great.

Fan operation in cold weather:
1. it should come on at start up
2. it should freely spin (1/4 to 1/2 revolution) if pushed when the engine is OFF
3. at above 40mph 60 kph we're relying on wind or air movement not the fan.
4. at slow speeds we're relying on the fan for cooling if required.
5. the fan requires power and therefore may cause a drop in engine rpm when it switches off.

Correct so far hopefully.

The truck in question (in cold weather approx -20deg c) runs fine at higher speed but at slower speeds, it would appear that the fan comes on stays on for awhile and when it cuts out causes a 500-700 rpm drop (which if stationary can cause a stall).

So based on the above: the truck likely has a cooling system problem: ie either fan clutch failing or thermostat issues.

Correct so far hopefully.

Fan clutch was replaced last winter... aftermarket parts so it could have failed.
Thermostat was replaced this fall after classic no heat issues. This combined with the truck registering normal temp on the dash (I know no precise but indicative) leads me to believe that the fan clutch may be faulty or sticky in cold weather... leading to when the fan comes on, it comes all the way on and attempts to do engine rpm speeds hence the noise and power requirement.

Correct so far? Yeah I know, in the time it has taken to type this I could probable get it fixed, but I'd like to actually understand what might be happening.

Comments on where I've lost the plot would help.

 

[martin]

Does the truck have a/c.?

 

[hey-you]

Yes there is A/C in the truck. Thinking back to the summer the A/C worked and definately produced cooler air.

A/C used in the winter to de-humidify cab air depending on the setting?

 

[Big Jim M]

Yes!

Yes there is A/C in the truck. Thinking back to the summer the A/C worked and definately produced cooler air.

A/C used in the winter to de-humidify cab air depending on the setting?

The compressor comes on when the heater control is set to DEFROST and the heated air is coming out to the windshield. The air is dried out by the A/C and heated at the same time.

This feature is of great use in Lousianna and Florida where the air is damp and the temperature isn't below freezing. However it is of little use when the temp is far below freezing. When traveling up north I always raise the hood and unplug the compressor in the winter..

Big JIm

 

[hey-you]

Okay, so being that the AC compressor is also in this loop .....I guess that that adds another element to check with respect to the sudden power loss.

Seeing as I normally end up driving with the heat on and on the screen (or screen floor mix) for pretty mush the entire winter, I should check that the AC compressor is properly cycling on and off.

I'm not sure how this relates to the fan (roaring) noise though.... as I would assume that the A/C would be dehumidifying from the time I pulled out of the drive and not just at slow speeds.

 

[hey-you]

Post shop visit

Well,

It been through more qualified mechanics then I am.... best I I got back was: You're not crazy.. it happens but like you said once its in park it cuts out faster then you can open the hood".

Best estimate was the thought that the IAC was acting up. Guess it can't hurt to pull it off and clean it....