I haven't always had this but especially here lately. When I start up the truck in the morning and don't give it more than a minute or two to idle, it sounds like the fan is on, exactly like when you pull a load and it gets warm, but yet it's cool outside. What the heck is this all about?

It dosen't take long to go away...less than 5 minutes. It is very annoying.

Mine does the same thing at times.. Cold start, running for 15 seconds before leaving.. the fan will run for 1/4-1/2 mile then disengage never hearing from it again the rest of the day.

Not sure why the fan does that exactly, but mine has always done the same thing pretty much since new. It seems the fan locks up after sitting a long time until the engine has run for a little bit getting it to freewheel again until hot.

mine does it randomly too.

on some random startups it will roar when I drive down the driveway. A minute later it shuts off and I never hear it again.

My 6.0 did the same thing. And my Duramax does too.

Perfectly normal

My 6.0 did the same thing. And my Duramax does too.

powerstroke or GM gasser?

Mine does the same thing but only in the morning. If it gets cold in the evening and I go out same OAT same time for warm up the fan doesn't come on. Been like that since I bought it I did ask the dealer he said it was normal (big suprise :confused: ).

yup, it is related to how the viscous coupled fan works there is a viscous fluid (silicone of some form IIRC) that in conjunction with a clockspring bi metalic strip that is temperature sensitive that couples the fan pulley to the actual fan blade. What happens is that if the motor sits for a while, like overnight, the silicone fluid may all move to the low point and couple the pulley to the fan blade on start up. It then has to be redistributed and then the fan will shut off again. It is pretty common on almost any vehicle with a viscous coupled fan. Thing is many of the vehicles today have electric fans so we aren't used to hearing this happen. Us old farts remember this same thing happening in the 60's and 70's when these fans first came into use.

Just give it a few hundred thousand miles to break in and calm down, it'll be fine!:D

I think all GM s do it. My 94 S-10 does it also. It's got 200,000 miles on it and its done it since it was new.

yup, it is related to how the viscous coupled fan works there is a viscous fluid (silicone of some form IIRC) that in conjunction with a clockspring bi metalic strip that is temperature sensitive that couples the fan pulley to the actual fan blade. What happens is that if the motor sits for a while, like overnight, the silicone fluid may all move to the low point and couple the pulley to the fan blade on start up. It then has to be redistributed and then the fan will shut off again. It is pretty common on almost any vehicle with a viscous coupled fan. Thing is many of the vehicles today have electric fans so we aren't used to hearing this happen. Us old farts remember this same thing happening in the 60's and 70's when these fans first came into use.


I thought there only existed horse and buggy back in those ice days of the 60s and 70s. Wow you guys had automobiles with fans!

If you turn the truck off the night before while it is extremely hot then the heat from the engine causes the fan cluth to engage IIRC and stay engaged until the rpm's get to about 2000 the next time you start it. My fan usually stays engaged until I hit the main road leaving my neighborhood, about 1/4 mile.

Mine does it too. On, off, on, off, on, off, oh you get the point. It's annoying; especially on a cold start and idle.

Wow, maybe there is something wrong with my truck because the fan has never come on when it is cold (before it warms up). :confuzeld

Do a search on "morning sickness". You will find a lot of info:)