I have just over a 100 miles on a complete restored 68 Chevelle with a 396 and a new 4-core radiator. The original stock fan shroud and clutch fan were used. It runs 190 down the Hwy all day, but in slow or stopped traffic the temp climbs to 210 degrees in 90 degree weather. I suspect my 45 year old clutch fan is the problem. So, I drove the car today and let it get to 205 degrees and shut the car off. When I grab the clutch fan, it spins fairly free (about the same resistance as it does when it is cold). I pulled the clutch fan and tested it the "red neck" way. I heated up my grill to 225 degrees and threw the clutch fan on it. It still spins with the same resistance as it does when it is cold. So, I'm assuming my clutch fan is toast and it is time to buy another one?? The local parts store has a Hayed HD 2747 in stock that I plan on replacing it with if the clutch fan is bad...........Am I on the right track?
BTW,your local parts guy made a mistake,hayden's 2747 hd thermal fan clutch is a great unit i often use ,but its for 69 & newer sbc/bbc chevelles w- long water pump and your 68 chevelle should have a short pump that doenst use that fan clutch that if used could possibly create improper fan to rad and fan to shroud spacing issues.
You could try it to see if its same dementions as your current original fan clutch and if yes then give it a try.
But the proper hayden thermal fan clutch by application per summit for your 68 chevelle with bbc with fan clutch and or AC is Haydens 2710 thermal fan clutch,heres a link to it.
From what you say i'd say the fan clutch is toast!
Good or bad theres no way i'd trust cooling duty to a 40+ yr old original fan clutch.buy a stock rep hayden thermal fan clutch from summit or rock auto (best prices) for your yr car with bbc & optional AC.
Along with the new thermal fan clutch to reduce temp a bit more do the following:
* Along with that great working quaility hayden thermal fan clutch buy & install an autzone 15356 stat with 3/16 bypass hole drilled in it .
* Seal any airgaps between rad core and fan shroud when adheasive backed foam insualtion avail from lowes etc ,that ensures all air moved by clutch fan is actuall pulled thru the rad core for max cooling vs thru gap between rad core and shorud which reduces cooling efficnecy.
* Use 30% anti frz/70% distilled water coolant mix for better heat transfer vs std 50/50 mix .
Doing all of the above with the new fan clutch should reduce cooling temp quite a bit esp with your new hd cooling 4 row rad as long your car/motor has proper short w-pump & clutch fan along with proper fan shroud too for your 68 chevelle with bbc with optional Ac or HD cooling option so everything fits properly and works as designed.
Let us know how much doing all of the above reduces cooling temp and dont disreguard the stat i rec because its an important part of reducing your enegine overall temp so dont overlook it!.