I replaced my clutch with the HD Hayden unit back in July. One thing I have not noticed, and everyone around here seems to mention, is that when the fan clutch engages you should be able to hear the fan roaring away. I have never heard my fan with either the factory unit, which I tested in the oven and was dead, or my new hayden. Should it be noticeable at highway speeds?

I was climbing a hill the other day in 35 degree whether and the needle started to move to the right of center. I had the grill blanket on, so thats partly to blame, but I never heard the fan engage.

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2006 CRD - GTB2056 turbo by Dieselguy86, Eco Trans Tune, Lift Pump, Week's, HDS Tstat, Racor Filter, ARP's, OME 790's+Top Plate, JBA 2.5", JBA UCA, Moab's+265/75R16, ARB Bull Bar, 4.10's, TrueTracs

I've never heard the mechanical fan "engage" on either of my 05s or my son's 06. When I had Kaps' fixed fan installed I could certainly hear it in city traffic but on the highway I could only hear it if I "listened". Hayden says their clutch engages when temps off the radiator are ca. 170F or about 30F below coolant temp. That said I have no clue what the real temps off the radiator are at CRD temps. That's complicated a bit by the clutch is never, to the best of my knowledge, fully disengaged so that the mechanical fan runs at "idle" all the time providing some cooling. Best I can say with engine OFF and cold reach in, ideally with glove on as fan blades can be sharp; and attempt to spin the fan - it should move stiffly but not spin freely.

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Sold to LOST member my 05 Ltd, GDE Stg II turbo + TCM tune, SunCoast TC w. Transgo kit, Steiger window regulators, Samcos, Fumoto valve, 2nd gen filter head with Lub. Spec. bleeder, Hayden clutch & 11 blade fan, inverted spare, P-1 battery, BF Goodrich Long Trail TAs, Etecno1 glow plugs, timing belt at 50K miles/8 yrs

It moves stiffly and I can use the blades to unthread and rethread the fan once I break it loose with a wrench, but so did my bad factory unit. My factory unit just never locked up after sitting in an oven at 200 degrees for an hour.

The other thing, I have the HDS Tstat at 203F and was wondering if it caused the clutch to engage all the time. I had a thread about this back before I bought the hayden but there was no clear answer.

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2006 CRD - GTB2056 turbo by Dieselguy86, Eco Trans Tune, Lift Pump, Week's, HDS Tstat, Racor Filter, ARP's, OME 790's+Top Plate, JBA 2.5", JBA UCA, Moab's+265/75R16, ARB Bull Bar, 4.10's, TrueTracs

I have the HDS tstat on my 05 and my son does on his 06, his on longer than mine, and both of us have Hayden clutches. Like I said neither of us have noticed the mechanical fan engaging but a) I have no clue what the actual temp off the "radiator" cooling stack is at operating temp; b) don't really know what temp the coolant is actually at at operating temp (tstat is only an indirect indicator - someone with the appropriate scan tool could likely get a reading); and c) neither of us have seen temps above dead vertical w/wo the HDS tstat and that included time my son's 06 was in Tempe, AZ in ambient temps well over 100F.

The fixed fan I had on for a while produced a barely perceptible drone at highway speed but was audible around town particularly at about 40mph. I assume that's about what the OEM fan sounds like with the clutch engaged. If so I doubt I'd notice it at highway speed.

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Sold to LOST member my 05 Ltd, GDE Stg II turbo + TCM tune, SunCoast TC w. Transgo kit, Steiger window regulators, Samcos, Fumoto valve, 2nd gen filter head with Lub. Spec. bleeder, Hayden clutch & 11 blade fan, inverted spare, P-1 battery, BF Goodrich Long Trail TAs, Etecno1 glow plugs, timing belt at 50K miles/8 yrs

I might be thinking about this wrong, but I'd imagine a higher temp thermostat would cause the fan clutch to engage less, since it's keeping more heat in the engine and letting less of it go to the radiator.

Sounds plausible.
The fan clutch is dependent on hot air being blown on it. So, if that air isn't hot enough...


This is why I have wired my electric fan to be on low speed at all times (I removed the engine driven fan). I have noticed on 2 occasions that while climbing a steep hill at slow speed there is not enough airflow to keep engine temp at a comfortable level.

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U.S. Army Retired

I would think this would be true until the thermostat opens. My T-stat is clearly going full open on hills around here so I imagine the fan clutch is getting the full 203F heat.





I gave up on my electric fan adventures. It wasnt cutting it at the altitude with the tune I want to run so I've just gone back to the mech fan. I would need to run like 4 FFD 12" fans to get the same airflow.

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2006 CRD - GTB2056 turbo by Dieselguy86, Eco Trans Tune, Lift Pump, Week's, HDS Tstat, Racor Filter, ARP's, OME 790's+Top Plate, JBA 2.5", JBA UCA, Moab's+265/75R16, ARB Bull Bar, 4.10's, TrueTracs