warp2diesel, I do enjoy, no sarcasm intended or implied, your posts but would put a slightly different spin, sorry, on this. IMHO, setting aside the durability issue with respect to the OEM fan clutch, the heat rise problem is not related all that much to how much air the 2 different fans move. Absent data I'm inclined to believe GDE that the nylon fan moves less but I'm not sure it matters. What matters is when in the heat cycle the fan clutch engages. As I understand it the OEM clutch engages fairly high up the overheat curve while the Hayden engages right at that curve's beginning.

In that sense I think doc4444 has a point - a fan clutch that kicks in high in the heat curve will have a hard time reducing temperature and may not be able to do so at all as long as the engine is under heavy load.

Bottom line - if I was to retain or replace a KJ clutch engaged fan on a limited budget the first thing I'd do is toss the junk OEM fan clutch and install a Hayden for the durability and earlier engagment. If I had some extra $s I might consider the nylon fan if only for the lighter weight but then I might save those $s toward an OME lift.

Let me see, the Bean Counter Engineered fan clutch with the plastic fan would not move as much air as the steel fan with the Bean Counter Engineered fan clutch. Further more the first fan clutches used on the '05s were worse than the '06 fan clutches as have been reported by several members. I would have to assume since I was not there, that Chrysler used the Bean Counter Engineered fan clutch in their development. Can someone verify my assumption?

For sure the fan clutch is not heavy duty. It was designed to have lower resistance when the clutch is disengaged to provide better fuel economy. The lockup curve is set high to help get the advertised EPA fuel economy rating. This ends up sacrificing clutch longevity as it undersized to begin with. Most manufacturers complete the severe duty testing with locked "on" fan clutches to avoid a clutch failure during the test process...funny! The clutch design probably works satisfactory for 70% of the CRDs doing light duty. The Hayden is for sure better for towing rigs based on comments here, not having seen or tested it. Is the Hayden unit much heavier than the stock? If it is, then the plastic fan might be a better compromise due to having less weight. The unsprung cantilevered mass should not increase much or it may affect the hub bearing life. That bearing is by no means overengineered.



Had they put their jar of ISO Approved serial numbered etched beans into the drawer which they use for counting when they designed the cooling fan/fan clutch assembly and, instead used the Hayden Heavy severe duty fan clutch, they would have gotten it right the first time.
According to the observations in this post on KJ, the plastic fan with the Hayden Severe duty fan clutch moves more air than the stock setup, having done so myself, I must agree. http://www.jeepkj.com/forum/showthread.php?t=48653

If the metal fan moves more air with the '05 fan clutch that turned out to be junk compared with the '06 fan clutch, does anyone even care?

You would only care if towing a heavy load up a 6% grade, mainly people out west. The overheat protection on the engine ends up dropping the vehicle max speed by 8-10mph if at wide open throttle for 20+ minutes. It would mean going from 46mph to 38mph.

Did the metal blades conduct more heat into the fan clutch to get it to turn on sooner?

For anyone who does care, they should mount manometers in front of the grill and in the engine compartment to check the differential pressure going up the mountain in 100F heat pulling 5000# load. Do the test under the same conditions with both the '05 fan clutch and metal fan Vs the Hayden severe duty fan clutch and plastic fan. Of course post the results for all of us to see.

I would bet the Hayden severe duty with the plastic fan will do better and the engine temp will be cooler. Use the Hayden severe duty clutch and plastic fan, you have the best of both.

I don't worship at the feet of engineers but I wouldn't totally blame them for these sort of problems. Blame needs to largely be placed at the feet of the bean counters who want to trim every last $0.00001 of cost out of the vehicle build price to reduce its cost point and increase profits and secondly to the questionable steps taken to meet emissions and CAFE requirements. Could they have installed a Hayden and the nylon fan in the first place, YES, would it have been consistent with emissions and CAFE, PROBABLY, would it have added say $5 to the cost of the vehicle, PROBABLY, hence you can see the decision coming from the bean counters.

I've owned a variety of vehicles both foreign and domestic and can say with confidence that every single one of them would have been significantly improved by ca. $100 more in various parts on the assembly line instead of $2,000 for the same parts after the fact.

I'm on my second 2 weeks camping trip this year and prior to hit the road I install the Hayden viscous clutch and the 11 blades nylon fan (OEM towing package for a 2002 AKA severe duty) This is a amazing combo, I climb several long road elevation in the Appalache with my 3000pds camping gear behind and never worry a second about overheating. EGT drop a lot faster a iddle so less time is need to cool the turbo before cutting the ignition. The severe duty viscous clutch from Hayden almost never engage in normal driving condition so using a lighter nylon fan with a more efficient viscous is just a very smart solution to the crappy OEM solution DC engineers came with.