It won't turn off???

[wylie1]

I have a 2006 LBZ with 103K on the engine. After repairs at that auto shop that included new trans cooler, radiator, etc, the fan that typically shuts off when your engine is warm, now stays on the entire time truck is running. It does not shut off a few blocks away after driving as it used to...Seems to be robbing some HP too.

Gets loud as ever when I accelerate. Any ideas if this is a thermostat setting for a cooler and which one?

Thanks in advance.

[CoyleJR]

It sounds like you are describing an electric fan. If you have one it is not factory, someone has added a aftermarket set up.
Additionally, was the truck in a wreck that damaged the cooling stack or were you having overheating issues? If you have the factory clutch fan (not electric) and the truck was in a wreck the fan could have been damaged and needs replaced. Kennedy Diesel sells some good replacement fans.

Good luck
John

[DmaxMaverick]

Sounds like you mean the engine-driven fan, driven by the accessory belt. While this type of failure isn't common, it does happen (a typical failure will just fail to engage when it should). If it doesn't disengage soon after a bit of driving following a cold start, it's likely seized or failed internally, or the bi-metal spring or shaft at the front is corroded or fouled. It is normal to take a while to slow down if it is left to idle after a cold start. If it was "normal" before, and is not now, it's likely failed. Even during the heat of summer, anywhere, there should not be enough heat from the cooling stack to keep it fully engaged after a cold start and some driving (although it may normally engage again while driving if it's really hot). In any case, it should be engaged for a short period after a cold start, disengage after a little driving, then engage again as temperatures require.

With the engine OFF (cold, or -preferred- several minutes after a hot shutdown), try to turn the fan by hand. It should turn w/o engaging the belt. It may have a bit more resistance when cold, but not much, it should still rotate. If it's hot, it should rotate fairly free with little resistance. If it's locked solid, or has a LOT of resistance (barely able to move it), the clutch needs replacement.

The good news is, they are not difficult to replace, or too costly (~$100). I recommend the Delco brand clutch. They are a little more $$, but are typically more reliable than aftermarket brands.

This applies to models up to 2010. 2011 and later have a different clutch, electrically controlled. Testing is similar, but requires additional electrical circuit testing.

[Kennedy]

Did the shop replace the viscous fan clutch?

The clutch can and will "engage" when cold depending on conditions at stutdown. Once started it should "pump out" the fluid after approx. 90 seconds of moderate RPM operation and then become "disengaged" which is a poor term. Moderately engaged is a better term as it will follow engine speed until a calibrated blade TQ is reached and hold there or below.