Can the fan clutch really be mistaken for the transmission acting up? I read this in the owners manual for the 2015 chevy express 2500. Anybody ever experienced this ? does this typically happen at low speeds?

"The vehicle has a clutched engine
cooling fan. When the clutch is
engaged, the fan spins faster to
provide more air to cool the engine.
In most everyday driving conditions,
the fan is spinning slower and the
clutch is not fully engaged. This
improves fuel economy and reduces
fan noise. Under heavy vehicle
loading, trailer towing, and/or high
outside temperatures, the fan speed
increases as the clutch more fully
engages, so an increase in fan
noise may be heard. This is normal
and should not be mistaken as the
transmission slipping or making
extra shifts. It is merely the cooling
system functioning properly. The fan
will slow down when additional
cooling is not required and the
clutch partially disengages.
This fan noise may be heard when
starting the engine. It will go away
as the fan clutch partially
disengages."

 

The fan will be fully engaged for a short time after a cold start. Especially if it's colder outside. When you drive it like that it will make a "whooshing" sound that sounds like the engine is spinning much faster than it is. It does feel like the engine is surging but the van isn't accelerating in response. It should disengage in less than a minute of driving.

The fan operates with a temp sensitive spring controlling a valve that lets centrifugal force move fluid in and out of chambers to control the engagement. The hotter the air flowing over the fan gets the more it engages. Cooler air flowing over it lets it relax and spin more freely. That's why it has the fins on it.

When it sits for a while the fluid pools in one spot which causes it to engage even though it's cool. A few minutes of idling or a short bit of driving will spin the fluid into place and relax the fan.

Sometimes the fans fail in a way that keeps them engaged. When that happens you'll hear the whoosh for longer after startup or all the time. If you go out first thing in the morning and move the fan by hand it will be stiff and not free spin. If you check it right after driving around the block it should spin freely by hand.

 

hey just wondering if you notice this on your rig, if it's the same on your rig. here it is

When I am driving on the free way at around 70mph my TAC says I am traveling at 2300 rpm. But as soon as a lift my FOOT a little of the gas pedal, the TRANNY shifts up to top gear, and the RPMS drop to 1700. What is up with that lol? just lifting my foot a little of the gas pedal does it. It won't really do it otherwise.

 

It should already be in top gear cruising at 70. Do you have the 4-speed?

Are you sure it's upshifting and not just releasing the locking torque converter and coasting?

 

I solve the problem by not looking at the "Tac.". You have the 6L90 right? 6 speed transmission with double overdrive shift all the time and never when you want. I've just learned to ignore it because I don't want to program it and worry about failing SMOG. Not only does it have 6 speeds but also looks up the torque converter variable amounts so they are really all over the place.

 

Yeah Ok I figured I was worried about nothing, 6 speed, yes.

 

Driving these vans over 70mph, even unloaded, takes quite a bit of power. They have the aerodynamics of a brick wall after all.

That said mine (2016/6.0) does comfortably stay in 6th gear at those speeds if I'm not towing. When towing, I pretty much only see 6th downhill or with a tailwind.