I've been reading on this forum for over a year but don't post much. BUT, I do have a question now. I've got a 2004.5 LLY but have never really pulled all that much since I bought it. I'm planning to get a gooseneck trailer for hauling my antique tractors to tractor pulls - just haven't done it yet. However, I did finally buy a 5er last week and pulling it home (100 miles) the fan came on repeatedly. I've got an Edge/Attitude so I could monitor the temp and I couldn't see any correlation between when the fan came on and the temp. Sometimes it would come on at 180 degrees - other times, 190 degrees. It would go off at odd times too. This was the first time I've ever had the fan come on since I got the truck, so I've had no previous experience. My son didn't know what was going on. I was only going about 65 the whole way but can't figure out the programming scheme for the fan. Can anyone shed some light on this for me???

Pretty typical. You'll rarely hear the fan unless you are pulling or pushed the truck really hard. When towing my 5ver it comes on at different temps as well, usually when pulling a hill and temps rise a bit, almost always when I stop the rig, then start moving again. Roars like crazy. Sounds normal to me. Later. JJ :)

Mine will come on only in the upper temps, something like 208 or so. It will stay on till about 193 194 or so. If I am pulling heavy and hit a hard hill it will not kick on fast enough, somewhere around the 218 - 220 area and stay on till the 193 area which is only after the hill is over.
Dan

I think the water temp is too slow to properly display the real temp of the cooling stack. Rapid changes in airflow like driving hwy 70 mph and suddenly slow down in hot climate will initiate that roaring fan to come on. Mine came on mainly in high altitude without pulling any load at all - no matter how fast I drove that fan came on every 3 min. (temp was over 110 F and altitude 5k in Arizona and also New Mexico).

It comes on at different times because it is only sensing the air coming through the radiator so air temperature, forward speed, and a lot of other factors can affect that

Birken

it will also come on when the engine is still cold.

It only comes on while cold long enough to pump the viscous fluid back out.

Pretty typical. You'll rarely hear the fan unless you are pulling or pushed the truck really hard. When towing my 5ver it comes on at different temps as well, usually when pulling a hill and temps rise a bit, almost always when I stop the rig, then start moving again. Roars like crazy. Sounds normal to me. Later. JJ :)

Well, if I may. Its been in the upper 90's here for the last week. And each day on my way home from work the fan has kicked in and stays on in stop and go traffic under 50mph. I am at 5700ft,stock and running empty.
Can this be normal? My old 6.0 never got on the fan even when pulling over Monarch Pass........ok it was really slow though.
Can't wait till I start pulling over the passes in the next few weeks......-:t

ps What is the purpose of the fan kicking in for the first few blocks on a totally cold start up??

Well, if I may. Its been in the upper 90's here for the last week. And each day on my way home from work the fan has kicked in and stays on in stop and go traffic under 50mph. I am at 5700ft,stock and running empty.
Can this be normal? My old 6.0 never got on the fan even when pulling over Monarch Pass........ok it was really slow though.
Can't wait till I start pulling over the passes in the next few weeks......-:t

ps What is the purpose of the fan kicking in for the first few blocks on a totally cold start up??

Its normal. Mine does the same thing - its the high altitude. Looks like GM took some precaution to bring on the fan early, is yours a 2005?

Like Tx said the fluid has to go back first from the day before (shutdown) - therefore the fan is on when cold in the morning.

So is the fan coming on the sound the truck makes that totally drowns out that wonderful diesel sound? To me it sounds like my wifes Tahoe when its wrapped up to 4600 RPM, yet there is no change in RPM of the Max when this roaring takes place.

I just Traded in my 6.0 F-350 on the max it never had the fan come on and sound like this thing does. it comes on at odd times and has nothing to do with the temp. I have noticed the Dmax seems to run much hotter than the 6.0 ford. My tranjy gage never went ove 140-160 on the ford, The duramax seem to run at 200 constanly. Once you go over 190 degrees transmision fluid tends to start breakin down. What is up with those high rpms on the highway.

So is the fan coming on the sound the truck makes that totally drowns out that wonderful diesel sound? To me it sounds like my wifes Tahoe when its wrapped up to 4600 RPM, yet there is no change in RPM of the Max when this roaring takes place.

Yes. Actually sounds like you've shifted down a gear or two, but the RPM's don't show it. I've noticed it a lot when you have been towing in hot weather, and you slow down for a stop light, sit for a sec (which allows the heat to build up in the radiator from the hot engine and A/C) and then you start off again...the fan is engaged and roars. Get back up to speed for a bit, and it drops off.

-JM