The fan will kick in when underhood temps plus coolant temps consistently go over 225 or so.
When the fan kicks off, a bi-metal strip and viscous coupling clutch will begin to make the fan go as fast as the crankshaft speed goes. It will vary fan speed as needed, making it go slower if needed.
The sound is equivalent (with the newer 8 bladed fan) to a light jet taking off in the distance. The older 10 bladed fans pushed more air through, but the noise made it sound like a jet engine was throttling up inside your engine compartment. Newer trucks (97 and up) will have the latest fan. The service bulletin came out in early 1998.
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1997.5 HMC4 Hummer H1 w/Slantback shell (Mine)
2006 Hummer H3 Adv. Package (Wife's)
M101A2 Trailer
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