2017 Peterbilt 389 - Fan Hub Won't Disengage - High Fuel Consumption

Question

My fan is locked on constantly. As soon as I build air pressure, it stays engaged. It's loud, I'm losing about 1 MPG, and the engine takes forever to get up to operating temp in the mornings.

I've checked the manual fan switch on the dash and it's in the 'Off' position. I've also checked the AC high pressure switch, as I know that can trigger the fan, but unplugging it doesn't stop the fan from spinning.

GrandmaGeartooth · Answer

✅ Confirmed fix: Found a tiny piece of debris inside the air passage of the fan hub assembly. It was preventing air from reaching the piston to push the clutch plates apart. Took the hub apart, cleaned the orifice, and replaced the o-rings. Works perfectly now.

ACAceAdam · Answer

Check the air line going to the fan hub itself. These hubs are 'spring engaged, air disengaged.' If you have a hole in the line or the seal in the hub is blown, it won't have enough pressure to pull the clutch away from the pulley.

2017 Peterbilt 389 - Fan Hub Won't Disengage - High Fuel Consumption

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