Just by coincindence, a discussion about the used of a 5-blade fan in comparison with a 7-blade fan as used on a GM thremo-controlled clutch occurred the last Saturday in June at the monthly "Cars and Coffee" outdoor car show. The several Corvette owners at the gathering agreed that the 5-blade fans coolled better than the 7-blade fan on their Corvettes and they said they have tried them both. According to the Vette owners, GM put 5-blade thermo-controlled clutch fans on Corvettes, with or without A.C.
That prompted me to experiment and change a 1992-1995 7-blade steel fan and thermo-controlled clutch back to the original 1991 5-blade steel fan and thermo-controlled clutch on my 1991 S10 Blazer 4x4. I immediately saw a slight improvement in cooling but only at highway speed with no difference in traffic. GM used a 5-blade steel fan on S10 Blazers with RPO C60 A.C. through 1991. Starting in 1992 through 1995, GM used a 7-blade steel fan and starting in 1996, GM used a 11-blade plastic fan arrangement.
Either a 5-blade or a 7-blade fan was standard equipment with RPO C60 A.C. The RPO C42, without A.C., were equipped with 3-blade fans. My 1963 Pontiac Cantalina with a RPO Police and Ambulance option without A.C. was equipped with a 5-blade solid fan, and no fan shroud. The 1963 Pontiac with Police and Ambulance option, witout A.C., had a low fin count, 3-tube radiator for improved air flow at high speed. Only the 1963 pontiacs equipped with A.C. had a fan shroud and thermo-controlled fan clutch.
There is no definitive proof which number of blades and what type of fan is best under all driving conditions.
Last edited by MouseFink; 07-16-2013 at 06:26 AM.