Diagnosing fan clutch issue (before I spend $600)

[brijn]

Hi,

Temperatures are dropping close to freezing where the bus is. On a test run I noticed that the fan was spinning very fast as soon as the engine started.

From what I understand they should be free spinning until a certain temperature, and I would expect that temperature to be well above freezing.

With the engine cooled down, when I spin the fan. It feels fairly free for about half the rotation, and then is much stiffer for about another half. I can still spin it however.

New fan is 900CAD from International, 500CAD from an aftermarket vendor. They must use unobtainium as the viscous fluid.

Before I replace, does my analysis make sense. Other things I can try? Most online content cover clutches that never engage. I will have good cooling, but lose power.

Bas

[brijn]

And i really should have looked at other posts. Very good thread not that long ago with some useful info

Will have a look at the build-masters stuff

[cadillackid]

kit-masters..


viscous fan clutches typically spin fast for the first couple minutes the truck is driven then turn off.. this is considered normal..
I was given a couple reasons for this.


1. the fluid in the clutch migrates when the clutch is stopped.. and its also very thick until the fan runs for a couple minutes. then it moves back to its correct chambers and shuts off..


2. some trucks using the same clutches had A/C condensors in front of the radiator.. when the engine is cold but the truck sat in hot weather, the fan needs to spin automatically on high speed to help the Air-cinditioner cool until the engine warms up and turns on the fan...



-Christopher

[brijn]

Hi,

Interesting, so in cold weather, it might actually take a bit longer for the fan to slow down since more heat will need to flow into the fluid before it can migrate back into the reservoir. Let me test it some more before replacing the clutch.

Tx for that info!!

Bas

[cadillackid]

My dev bus and my fancy pickup truck both run the fan for the first couple miles I drive. Idle doesn’t typically turn it off unless it’s in high idle.. I put a Horton clutch on the red bus so it’s instant on or off