Jump to content
  • Sign up for FREE! Become a GM-Trucks.com Member Today!

    In 20 seconds you can become part of the worlds largest and oldest community discussing General Motors, Chevrolet and GMC branded pickups, crossovers, and SUVs. From buying research to owner support, join 1.5 MILLION GM Truck Enthusiasts every month who use GM-Trucks.com as a daily part of their ownership experience. 

Fan Clutch Overzealous; 2003 GMC Sierra 1500 4.8L 2WD SCSB

Recommended Posts



About 3 or 4 years ago, the subject truck was my dad's.  And everywhere he went, the coolant fan would be roaring.  So, long story short I wound up putting the (seemingly) lowest duty fan clutch on it I could source.  In the end, it worked as original.  The first maybe 1/8th of a mile after cranking the fan would be engaged, but it would drop out and run quiet.


I'll mention, the truck has had an easy life.  It has towed very little.  And when it did tow, it towed very little.  It towed a decent load one time.


Anyway, the current problem is, that if I crank the truck with the A/C already on, the fan will stay engaged and roaring.  Yet if I crank it with the A/C off and drive it until the fan decouples, then turn the A/C on, the fan will remain decoupled.  But once that fan comes on, with the A/C on, it will not decouple, and will roar and roar and roar.  Even with driving the truck around like I'm driving Ms. Daisy.  I know the coolant is not getting hot.  The gauge is down in the 190° like it always is.


I think this fan is strictly a viscous coupling, I don't believe there is any electronic control with this fan whatsoever.  Can anyone confirm that for this generation?


It's annoying to be driving around nice and easy and have the fan roaring, and I'm sure it is less fuel efficient with that fan roaring.  I realize it's been stifling hot down here in the dirty dirty south, but surely it should take more than the temps being in the 90's to pull the fan into engaged.  Maybe for a short distance until the cool air is flowing through the grill, but it should drop out soon after.  There's got to be more to this viscous fan clutch than I am aware.


If it is just a viscous coupling controlling the fan only, I suppose this fan clutch could be on its way out as well.  I would appreciate any feedback!

Link to comment
Share on other sites

If I remember correctly the less expensive fan clutch uses a silicon fluid that gets more viscous the warmer it gets thus engaging the fan, the more expensive 1s have a mechanical thermostat that's visible on the front of the clutch. the ac is probably dumping too much heat for it to disengage even at speed so normal operation maybe. the efans in my Caddy never seem to shut down either with the ac on but that may be more head pressure than temp causing that

Link to comment
Share on other sites

Thanks Richard.  Seems I remember there being a metal coil on the front of the replacement one, but I'm not 100% on that.  I searched on here for normal operating temperature because I was concerned maybe my radiator might be a bit plugged.  But according to what I read, my 4.8L is spot on everyone else's.


Mine seems to run (by the best estimate of the gauge reading) between 195° and 200° WITHOUT the A/C.  Maybe a skosh warmer than that in lots of stop n go traffic.  WITH the A/C on, it seems to run about 8° warmer.  Something like 205° to almost the 210° mark.  And it seems that ~205° is the threshold to activate the fan clutch on this truck.


The cooling system seems to be nominal, I double checked the oil level (been a while since an oil change and it was perfect at the top and looked very healthy, was impressed), the A/C blows ice cold.  So, it could be just as you say, maybe it is dumping warm air right on the front of that fan clutch.


I'm interested in running a fan clutch that engages minimally as this truck really only hauls my fat ass around.  Not much more.  I was studying up on part numbers.  There are 2 fan clutch part numbers for my truck in all the info I found.

  • 15911779:  This seems to a little LESS heavy duty.  It reads like it is for some of these generation trucks WITHOUT A/C.  However, WITHOUT A/C trucks are going to run cooler than those with A/C (when the A/C is on anyway).  So maybe this fan clutch has to engage at lower heat levels.  I.E. Let's say they're pulling 5,000 pounds.  The one without A/C is going to be running cooler than the one with, yet may still need more air pulled through the radiator ... so maybe this one activates at lower temp.
  • 20913877:  This one seems to be the one for trucks with A/C.

However, how it is worded it seems to say the 15911779 one is for 4.8L trucks.


Exact wording:  "All models. 6.0l. All models. 5.3l. 5.3 & 6.0L, without ac. 2000-04, without ac. All models. 4.8l. All models. 4.3l. 4.3L, 1999-04, without ac. 5.3, 6.0L 2002-04, 8.1L. Helps quiet noisy cooling fans with stuck fan clutches\ This GM Genuine Part is designed, engineered, and tested to rigorous standards and is backed by General Motors\ Original equipment parts are designed to work with your GM vehicle safety systems -- aftermarket replacement parts may not meet the same OE safety regulations, depending on the part type."


Gonna break that down below to see if I can make sense of it.


All models. 6.0l.

All models. 5.3l. 5.3 & 6.0L, without ac.  2000-04, without ac.

All models. 4.8l.

All models. 4.3l. 4.3L, 1999-04, without ac.

5.3, 6.0L 2002-04, 8.1L.


In any event, it is not clear.  I have the old original part, and pictures of it, but it does not have either of those 2 part numbers on it.  It has these numbers on the front of it:  7E11F2 (printed / stamped), AAAD (printed / stamped), a small G53A (embossed / cast).  On the back it does have AC and 5.1 (embossed / cast) on it.  So I suppose that would direct me to the 20913877 part number.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...

Important Information

By using this site, you agree to our Terms of Use.