Question? Did my 75 Stingray come with a fan clutch.?????

Ok, why do I need one. What is its main purpose.......jim

Please Help with  this...

I'll take a stab at this as long as more technical folks don't hurt themselves laughing too much.

To the best of my knowledge most, if not all, C3 years used fan clutches.  At idle and lower speeds they engage to make the fan pull air through the radiator.  As vehicle speed and airflow increase they allow the fan to "free-wheel" and not be a drag on the engine.  There is also a thermal sensor in them that will engage the fan when things get too warm under the hood regardless of vehicle speed and airflow.

If you choose not to use one installing electric fans with a thermal sensor would be the best alternative.

Ok "techies" - have at it.

(Sorry, Jim,....couldn't help meself!!)

Norsky is correct. All Sharks had fan clutches that I know of, even the mighty L-88. The clutch is there to keep from taking too much HP from the engine, when the fan is not really needed, such as driving down the highway. You can replace with a solid fan, but it is not recommended. Adams' Apple38880.7347569444

It is important to keep in mind that if you use a engine driven fan, that a fan shroud be used as well as the radiator to radiator support seals be in good condition. I just went through this whole deal, with a new radiator, shroud seals, water pump, heater hoses, radiator hoses and trans cooler hoses. I'm still using the engine driven fan, but may go to electrics.

Dave

I have no problems with my flex fan.  I prefer them to the clutch type because the clutches always crap themselves in time.  The flex fan on the other hand gives good air flow when the car (and engine) is moving slowly and as the engine revs increase the blades flatten out and tend to use the speed of the car for air flow.  with the blades flattened out, there's less "drag" on the fan thus less HP loss trying to drive the fan.

Electric fans would be the best though with a sensor IN the coolant (intake fitting). But if you want to keep the original look of your vette, I recommend a flex fan with the original shrouds.  Shrouds are a must with vettes due to the position of the radiator.  I haven't seen any electric fans with the shroud still fitted.  Anyone?

I use a 17" flex with a shroud & a 16" Spal puller when I'm in traffic which is on a on/off switch controled be me. Never goes above 185 in 90 degee weather w/air on.

Alan

Norsky did a good job.  But here is more detail.

The fan clutches come in two types.  Thermo, and non thermo.

Non thermal fans have a silicone type fluid in them.  This fluid causes resistance to movement, but is still a thick liquid.  At low engine speeds the fan turns at close to the same speed as the water pump shaft, which is relative to engine speed.  As the speed of the fan increased the drag caused by the blades creates more force in resistance to turning.  This causes the fan clutch to slip.  The fan does speed up a bit more, but less and less relative to engine speed.  The engine speeds up much more.  It does NOT reduce drag, it DOES prevent drag from increasing much.  So the drag builds quite a bit when started and revved up some, the becomes more constant speed and drag dispite engine speed increases.  This insures a constant flow of air across the fan, and in turn A/C condenser and radiator.

Without this steady state drag, as the engine speeds up more, the fan would continue to create more and more drag, and thus require a lot of horsepower that would not get to the wheels.  It also drops fuel mileage due to increased drag, as well as creates a lot of fan noise.  It is not necessary for the fan to ever run this fast, or create this much drag to cool.

Thermo fans are much the same with one difference.  There have a bi-metallic temperature strip on the front of the fan clutch.  The strip rotates a valve in the clutch, and varies it's resistance to turning.  So a cold fan can spin with little resistance, and then turns slower and creates less drag on the engine.  As the bi-metallic strip heats from heat off of the radiator, the valve starts to close and increases resistance and thus torque transfer.  The fan creates more drag, but turns faster to creates more air flow, and cools more.   It is self regulating based on air temp.   Now there is more drag only when needed.

A flex fan does not slip, and the rpm always matches the water pump shaft / engine speed.  But it does reduce drag.  As it spins faster, more force is created to move air.  This resistance against the blades make the blades flatten out.  The flatter blade moves less air, creating less flow.  Again it's self regulating.  The faster it goes the flatter is gets.  But it does not move less air as it flattens.  This is due to the fact it is moving much faster as it flattens.  The two offset, and about the same volume of air is moved, at the same resistance or drag quanity.

The advantage of the flex fan over the other is there is less weight to move and rotate.  That cuts torque load a bit, and provides more power out of the back of the engine.  But they typically don't move as much air as the original fan set up.  There are exceptions to this.

Electric fans produce very little drag on the engine.  But the power created by the alternator to supply the electric does create some drag.  They move a lot of air, but only in their fan area.  Due to the fact they are so close to the radiator, the do not move air through the entire surface of the radiator.  This reduces cooling.  Single or dual fans  systems can be used.  Whichever covers more radiator surface area cools better.  Sometimes the increased air flow from an electric will cool the smaller area enough that cooling increases overall, sometimes the opposite is true, and total cooling is reduced. A mechanical fan and a shroud moves air through the entire surface of the radiator.

If electric fans are thermostaticly operated, the engine temp raises and drops as the fans cycle.  Most new cars do this.  But the temp can be over 230 degrees before the fan kicks on.  They are usually shut off by 200 or 210 degrees.  Generally there is enough air moving through the radiator above 35 miles per hour that the fan is not needed.  So an electric fan does not come on.  Due to the design of our sharks this speed is often not adaquite for air flow and a fan can still be needed. 

In no case is a mechanical fan, solid, flex, clutch, or thermo clutch affected by road speed.  Only engine speed.

The 'Master' has spoken.  And 'Grasshopper' is again in awe of his wisdom!     

OK GUYS HERE IS WHAT I DID FIRST I BOUGHT A KIT TO CONVERT MY FAN TO DIRECT DRIVE. WOW REALLY COOLES THE CAR DOWN. I LIKE IT BUT REALLY ADDS TO THE NOISE LEVEL AND ALTHOUGH THEY DONT TELL YOU UP FRONT ITS ONLY GOOD FOR 4500RPMS. WELL WHEN YOU HIT THEM FOUR BARRELS IT GOES RIGHT TO 4500RPM'S. SO I DICIDED ON A FLEX FAN THATS GOOD FOR 10,000RPM"S WITH THEIR INSTALL KIT.ILL KEEP YOU INFORMED. BUYING IT FROM         &n bsp;   JEG'S.COM   THANKS GUYS

IT

TO KSTYER YOU SHOULD BE AN ENGINEER....