When I stand in front of my truck with it running, its sounds like a fan turning on and off. What is that? And BTW, I got the fuel filter changed, no problem. Fired right back up.

 

Do you have your defroster or A/C on when it is doing this? Could possibly be the sound of your AC clutch kicking on and off.

 

I agree, its the defroster I'd bet.

 

no, I don't have the ac or defrost on. It sounds like its coming from the grill. Its sounds just like an electric radiator fan coming on and off about every 10 seconds. I thought maybe it had somethibng to do with the innercooler or turbo maybe.

 

That is likely the sound of the thermostatic fan clutch partially engaging and releasing as the fan spins. When pulling a load on a hot day, you will hear a roar as the high temperature causes the fan clutch to lock up. You are hearing a small amount of that.

 

What is this fan clutch, exactly? It prevents the fan from spinning until a thermostat gets to a certain temp, then locks up a clutch the locks the fan onto the shaft snout?

 

Yes. The hub of the fan has a cast aluminum finned housing. Inside this hub is a viscous fluid with a heat sensitive bi-metal spring facing forward. When the engine is sitting (not running) the fluid will settle and the fan will run for a minute or more (depending on outside temp and the speed the engine is running at) until the fluid warms and evens out in the hub. As the temp rises the bi-metal spring turns a shaft directing more fluid to the clutch engaging the fan. More temp the faster the fan will turn.

These units work well for most applications. However when fully engaged they still are not a full 1 to 1 speed with the engine. 5 to 10% slippage from the clutch is normal. When disengaged they tend to turn at less the 50% of the engine speed.

Also when these units fail they can either fail fully locked up, or at some state of unlocked and fail to cool when you really need it.

Start a cold engine, rev the engine up slowly and you should be able to hear the fan. If the fan clutch is working you should be able to hold the engine at this speed and hear the fan noise drop off after a min or two.

Horton makes a electric fan clutch that is either on or off. Is hooked up automatic through a thermostatic switch and can also be turned on manualy from the cab with the flip of a toggle switch. These units are spendy. If memory serves me correct, $600.00 to $800.00 range.

 

boiler-rat is the sound you hear when you first start it on a cold morning? If so it could be the grid heaters cycling- when mine turn on it draws so much juice that it sounds like what your describing. I think its the alt. whining a little under the load.

 

The grid heater idea will be accompanied by a noticable dip in the alternator gauge too...that's a dead giveaway if the noise is from there...

pb...