Fan clutch staying locked on.

[1998_K1500_Sub]

What are the parameters of a stock fan. Kick in at temp. ,disengage at speed etc....?

In one particular case (my K1500):

This following process happened repeatedly, as the thermostat opened and closed. This was observed on a ~80F day, engine idling, hood open, OE fan clutch, vehicle stationary while I was working in the engine bay. Bear in mind the thermostat may not have been literally "closed" in this situation, but it was allowing significantly reduced flow to the radiator as compared to "opened". Read on...

When the thermostat opened, the temperature of air flow through the radiator rose rapidly ("air flow" being induced by fan, but running at lower speed as the clutch was relaxed). Shortly thereafter (5-10s maybe? I'm going from memory) the fan clutch tightened and the fan really started moving air (and of course, HOT air and a lot of it).

When the thermostat thereafter closed (perhaps 30s later, give of take), the air temp through the radiator dropped off and soon the fan clutch relaxed and the airflow diminished.

Net-net AFAIK is the clutch tightens when it's beneficial to do, and relaxes otherwise.

I know this is simply an observation of one particular clutch, and neither a specification nor a broad sampling of clutch behavior, but since nobody's responded yet I figured I would toss this out.

 

[L31MaxExpress]

In one particular case (my K1500):

This following process happened repeatedly, as the thermostat opened and closed. This was observed on a ~80F day, engine idling, hood open, OE fan clutch, vehicle stationary while I was working in the engine bay. Bear in mind the thermostat may not have been literally "closed" in this situation, but it was allowing significantly reduced flow to the radiator as compared to "opened". Read on...

When the thermostat opened, the temperature of air flow through the radiator rose rapidly ("air flow" being induced by fan, but running at lower speed as the clutch was relaxed). Shortly thereafter (5-10s maybe? I'm going from memory) the fan clutch tightened and the fan really started moving air (and of course, HOT air and a lot of it).

When the thermostat thereafter closed (perhaps 30s later, give of take), the air temp through the radiator dropped off and soon the fan clutch relaxed and the airflow diminished.

Net-net AFAIK is the clutch tightens when it's beneficial to do, and relaxes otherwise.

I know this is simply an observation of one particular clutch, and neither a specification nor a broad sampling of clutch behavior, but since nobody's responded yet I figured I would toss this out.

Observation I had in 30°F weather with the Duramax fan and TBSS severe duty clutch on my 5.7L. At idle with the engine warmed up the clutch was pulsing to regulate temps. Maybe 5 seconds of higher speed and 30 seconds at near total freewheel. By freewheeling I mean it sounded like the fan was not even turning.

Also on the dyno on a 100°F day. Made 2 pulls with minimal clutch engagement. 3rd pull got aborted due to a WOT downshift. By the start of the now 4th pull the clutch fan was starting to couple pretty good. Lost 18 ft/lbs of torque near peak torque but only about 8 hp up top. Duramax fan was roaring on that pull and the engine temps came down nearly 15°F during the pull. Started the pull around 189°F and came down to 174ish by the time the engine spun up to the fuel kill. Clutch fan could eat a fair bit of power but never even came close to letting the engine run hot and the a/c stayed ice cold even at idle. At idle on a 105°F day it would sit around 38-42°F out of the vents on both ends with the blowers on high using recirculate.

xc_hide_links_from_guests_guests_error_hide_media