I am going to install an 18" 7 blade clutch fan on my dart this weekend and I am not sure which fan clutch to use. Should I get the regular spring loaded or the thermal type?
Advance auto parts sells 3 different fan clutches for '70-'71 A body cars, non-thermal, thermal, and heavy duty thermal. Which would be correct for a 340 equipped A body?
That's what I was thinking. Why is there a heavy duty thermal? I saw a picture of it and there were fins in the center part of it also. I can see a difference visually, but what would be the need for one so beefed up?
Use thermal only. If your fan blade is larger than 18" and the blade pitch is greater then 2-3/4" then you may need a HD model clutch. From the factory all Darts came with a standard thermal clutch. Darts just don't have clutch to radiator clearance for the HD type clutch.
No American made car has ever come from the factory with a non-thermal clutch.
It's been my experience that the standard fan clutch will not spin the heavier 7 blade fan fast enough at low speed or idle therefore your car will get hot at idle. The HD one works great with the 7 blade fan on my cars. Idle 90*+ with the A/C on and does not heat up at all. I can't comment on the clearence issue though as I have E-Bodies.