Fan Clutch Testing

[Craig Jewett]

Does anyone know of a procedure to test the fan clutch ? The only method I know of is to check how much effort is required to spin the fan by hand when the engine is hot (engine off, of course). I believe it should require much more effort to spin the fan when hot. Naturally, mine doesn't seem to change much at all between cold and hot. The temp gauge always stays just to the left of the number "2" in the "210" on the gauge, which I think is about 180 degrees F, where it should be. Do these clutches gradually fail or do they usually just quit ? Any suggestions are appreciated...

Thanks in advance

Craig Jewett # 28049 '67 L-79 A/C coupe

[Jack H.]

Re: Fan Clutch Testing

Can clutch can wear/fail. Inner cavities consist of silicon based lube res, thermostatic and inertia controlled trap door and 'race way' where fluid runs between upper/lower set of fins. Amount of fluid in race way dictates viscous friction level between fins and the degree of clutch engage/disengage. Each fan clutch had a pre- defined 'slip' curve based on CFM air flow needs of host power plant, cooling system and rotational inertia/drag characteristics of factory stock fan. In general, relationship was of this nature:

RPM I I -------------- I I I I I I I I I-------- I ________________________________ Temperature

where clutch made transistion from full engage drag to full release slip based on BOTH ambient temp as well as rotation speed.

Playing by hand you can get 'something' of a feel for where your clutch is today, but you'll not get real specific unless you've got a well educated 'touch' for the system. There are several including NCRS member Fred Oliva at Vintage Automotive Research (see archieves) who specialize in opening and restoring factory original fan clutch assys to factory (or user defined) specs.

Many factors affect temp gauge readings and this subject too, is discussed in several archieve threads. Basically, a 'healthy' Corvette should display steady state temp readings 10-15 degrees above thermostat 'pop' point. This is a VERY GENERAL rule of thumb that will vary with ambient, MY, engine, and options.

You'll find rule of thumb 'touch' guidelines for thermostatic clutch operation in the NCRS Performance Verification manual on your MY Corvette (available NCRS Cincy library) because in a PV test, judges need to determine gross operability of various components during/after road testing.

[Jack H.]

Re: Fan Clutch Testing

Can clutch can wear/fail. Inner cavities consist of silicon based lube res, thermostatic and inertia controlled trap door and 'race way' where fluid runs between upper/lower set of fins. Amount of fluid in race way dictates viscous friction level between fins and the degree of clutch engage/disengage. Each fan clutch had a pre- defined 'slip' curve based on CFM air flow needs of host power plant, cooling system and rotational inertia/drag characteristics of factory stock fan. In general, relationship was of this nature:

RPM I I -------------- I I I I I I I I I-------- I ________________________________ Temperature

where clutch made transistion from full engage drag to full release slip based on BOTH ambient temp as well as rotation speed.

Playing by hand you can get 'something' of a feel for where your clutch is today, but you'll not get real specific unless you've got a well educated 'touch' for the system. There are several including NCRS member Fred Oliva at Vintage Automotive Research (see archieves) who specialize in opening and restoring factory original fan clutch assys to factory (or user defined) specs.

Many factors affect temp gauge readings and this subject too, is discussed in several archieve threads. Basically, a 'healthy' Corvette should display steady state temp readings 10-15 degrees above thermostat 'pop' point. This is a VERY GENERAL rule of thumb that will vary with ambient, MY, engine, and options.

You'll find rule of thumb 'touch' guidelines for thermostatic clutch operation in the NCRS Performance Verification manual on your MY Corvette (available NCRS Cincy library) because in a PV test, judges need to determine gross operability of various components during/after road testing.