snip from here
"Now, here is where some folks join in the fray with Heavy Duty Fan Clutches and Flex Fans and such. Kind of makes you wonder if enough consideration was given to the other areas of the closed loop system.
That this solution has worked for so many is a testimony to the fact that the closed loop system probably worked when the vehicle was new, but being twenty to thirty years old and bored over as most of our rigs are, problems are bound to crop up. Also consider the fact that the radiators most of us are using are probably not nearly new with some blocked passages, and the ole water pumps have impeller blades eaten by cavitations. That thermostat we just put in last year was a bargain for $3.87 at the local auto parts store, and the coolant is probably more like 80% antifreeze to 20% tap water. All of which has resulted in coolant dissolved solids and minerals and calcium deposits throughout the system over the years; it is no wonder that we spout off so about any kind of improvement at all.
So, adding that heavy-duty fan clutch gets just enough oomph to get us over the hump and is universally agreed upon as the Holy Grail of Cooling.
Well, it is not a bad idea, my ONLY problem with this solution is that if we address the engineering behind the Heavy Duty Fan Clutch we find that it is designed to prevent the fan from turning at the same rate of the water pump shaft. Regular duty fan clutches operate at about 50-60% of shaft speed, and heavy-duty fan clutches are in the 60-70% range. A severe duty fan clutch will operate at 90% of its shaft speed. All will slip much more as the temperature of the silicon cools down a bit at high speeds.
This gives quieter operation (no howling) and perhaps better gas mileage. Also at higher speeds, the fan is spinning more freely and thus it frees up horsepower and allows more air to flow through the front of the radiator. Which brings up another issue, air dams can build up so as to prevent some air entering the engine compartment, due to the raised height and flow path of air underneath our rigs. On some lifted vehicles, an air dam can from underneath the front bumper to the front engine area, thus making it harder for heated air from the radiator to escape, and thus affecting the bi-metallic spring on the front of the fan clutch. Removing the hood and driving around a bit will reveal this odd occurrence.
Once we put this into perspective, we realize that the fan clutch is in reality a boon to those systems that have been designed and are in the middle of their operational parameters, so that the clutch can slip when additional airflow may not be needed, or additional air flow may be available when required, by having the clutch engage the fan and not allow it to slip as much.
Of note on fan themselves, is that AMC originally stipulated a 19.5 inch 7-blade fan, probably around a 2-inch pitch.
I just wanted to throw some things out there to consider, before everyone just starts to tear into their rigs and throw parts at potential problems, plus share some of the things that I have observed along the way."
In the middle of the last trail-ride, the fan clutch decided to spray silicone all over (again) #-o (Seems my pile of used junk has run out)
I plan on installing my new Hayden (P/N 2797) Severe Duty Fan Clutch tomorrow (runs 80-90% of water pump speed). Hopefully this is the last clutch I put in and the extra noise does not cause me to shoot it.
Hayden P/N 2747 is a 100% bolt-on Heavy Duty fan clutch for AMC V8's and a myriad of others... It runs 10-15% slower than the severe duty when engaged.
If this does not work, I'm going to follow the crowd and go Tarus fan....... Anyone got a 500A alt? Maybe I could pilfer the batteries from a Prius?
:razz:
