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The fan-like noise can happen warm or cold but always when asking the truck to move. Never stationary. At first I considered the cooling fan on the engine- but that should not be kicking in when it is just started up and put into motion. It is also something I can’t quite see while rolling down the road.
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Working as designed. I'll explain in more detail below.
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Sometimes, I can nearly complete a 30 mile trip and never hear the sound only to have it kick in as I start moving again at the stop sign down the street from my house. Occasionally, it seems a little hesitant to shift (only when fan sound is already present) and if I keep pushing down on the accelerator I get a terrible whine. The whine will go away as soon as I let up on the accelerator or the transmission up-shifts.
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Okay, here's the deal. The fan drive engages based on the temperature of the air coming out of the heat exchangers in front of the fan. At about 185F air temp (and look up a half-dozen recent posts from me about why this air temp is less than the coolant temp), the fan drive engages. Now, while you're running down the road, pulling your trailer (or not: on a hot day, with the AC on, mine will do this without the trailer), stuff is making heat, but there's air flowing through thanks to the vehicle speed. Now you come to a stoplight. Air basically stops. Air temp goes up -- there's still all that heat to deal with -- and the fan drive engages. But... it's not turning fast enough to be audible until the light changes and you accelerate away. You'll probably start to hear the fan somewhere above 1600-1800 engine RPM (I hear mine at about 1400-1500, but I'm also someone who is very well-tuned to this particular sound since it's key to what I do for a living).
And now you're up to speed again, air is moving through the exchangers, the air temp drops, and the fan drive disengages, lowering the fan speed enough that the noise goes away. Only to return at the next stoplight.
That part of it is entirely normal. It'll also do it after sitting overnight -- this is called "morning sickness" by fan drive engineers -- and will take a little bit for the drive to "pump out" when you first pull away in the morning.
The fan-like noise can happen warm or cold but always when asking the truck to move. Never stationary. At first I considered the cooling fan on the engine- but that should not be kicking in when it is just started up and put into motion. It is also something I can’t quite see while rolling down the road.
[/ QUOTE ]
Working as designed. I'll explain in more detail below.
[ QUOTE ]
Sometimes, I can nearly complete a 30 mile trip and never hear the sound only to have it kick in as I start moving again at the stop sign down the street from my house. Occasionally, it seems a little hesitant to shift (only when fan sound is already present) and if I keep pushing down on the accelerator I get a terrible whine. The whine will go away as soon as I let up on the accelerator or the transmission up-shifts.
[/ QUOTE ]
Okay, here's the deal. The fan drive engages based on the temperature of the air coming out of the heat exchangers in front of the fan. At about 185F air temp (and look up a half-dozen recent posts from me about why this air temp is less than the coolant temp), the fan drive engages. Now, while you're running down the road, pulling your trailer (or not: on a hot day, with the AC on, mine will do this without the trailer), stuff is making heat, but there's air flowing through thanks to the vehicle speed. Now you come to a stoplight. Air basically stops. Air temp goes up -- there's still all that heat to deal with -- and the fan drive engages. But... it's not turning fast enough to be audible until the light changes and you accelerate away. You'll probably start to hear the fan somewhere above 1600-1800 engine RPM (I hear mine at about 1400-1500, but I'm also someone who is very well-tuned to this particular sound since it's key to what I do for a living).
And now you're up to speed again, air is moving through the exchangers, the air temp drops, and the fan drive disengages, lowering the fan speed enough that the noise goes away. Only to return at the next stoplight.
That part of it is entirely normal. It'll also do it after sitting overnight -- this is called "morning sickness" by fan drive engineers -- and will take a little bit for the drive to "pump out" when you first pull away in the morning.
