It's been several years since I've owned a vehicle with an engine mounted cooling fan. I have a 1999 silverado and I notice that the fan runs all the time...is this normal. It was 35 degress last night and I cranked it up and the fan was running wide open. I thought the fan should only start running once the engine gets to operating temp or is running a little hot??

 

If the fan is running all the time you may have a bad thermostat, or a bad relay. Anybody else have any ideas?

 

I just replaced the water pump and thermostat. Truck is running at normal operating temp...everything seems ok....just wondered if it should run all the time. What does the fan clutch do? How is it engaged or disengaged?

 

You have the engine mounted fan? The fan clutch does engage and disengage the fan. However the fan will not completely disengage. It will be spinning all of the time, but you will be able to notice a difference in the sound and the RPM's when it is fully engaged. How it works: it has a coil in the clutch that expands when it get's warm and engages the clutch to start pulling a lot of air. After it has cooled down the air that is drawn in the radiator it will disengage and not spin as fast and aggressive. To check to see if it is bad, turn off the motor when cool and grab the blades and tweek them from bottom to top to check the bearings. (Bearings failing are the most common things to go out in a fan clutch which makes it not work right) Then make sure it spinns somewhat freely and then go drive the truck and make sure to get it good and warm, (Ideling in the driveway will not get it warm enough) and quickly park it and turn off the motor. Then dothe spin test and there should be more tension on the fan when hot. If it is really free or really tough when it shouldn't be then the cluch has gone out.

The fan clutch is really easy to change with normal hand tools. Also make sure that the water pump is not loosing it's bearing as well while you are there. But you just replaced it so it should be good. But you never know!!!!!!!

Have fun, and what ever you do, DO NOT GRAB THE FAN WHILE THE TRUCK IS RUNNING!!! I cannot tell you how many people I have seen do it! It's funny to me though.