Fan Blades

Discussion in 'The Bench' started by blue suncoupe, Jul 19, 2019.

  1. blue suncoupe

    blue suncoupe Well-Known Member

    The 1972 GS 455 with A/C calls for a 20" 5 blade fan. I have a 20" 7 blade ( I think it from a Riv) if I am correct. Is there that much of a difference?
     
  2. 1972Mach1

    1972Mach1 Just some M.M.O.G. guy.....

    Besides the fact that one has 2 more blades than the other?
     
  3. blue suncoupe

    blue suncoupe Well-Known Member

    Right good one lol. I think the 5 blade moves more air, I have a bit of a overheating issue and thought of getting the 5 blade to replace the 7 blade but, if it's not going to help I will leave the 7 blade on.
     
  4. 1972Mach1

    1972Mach1 Just some M.M.O.G. guy.....

    Hahaha.....well, in theory the 7 blade should cool better actually. What have you tried to fix the issue? When does it happen? Do you have a shroud, and if so how far into it is the fan blades? They should be about half in and half out of the shroud as a general rule of thumb.
     
  5. blue suncoupe

    blue suncoupe Well-Known Member

    I have some temp testing equipment that I used when I worked on boilers. I was thinking of hooking one lead up to intake manifold and the other to lower rad hose. I cam monitor engine temp, return from rad temp and the differential of the two. Oh I guess that would de distracted driving.
     
  6. blue suncoupe

    blue suncoupe Well-Known Member

    It overheated while running the A/C and in traffic. I had a 3 row brass/copper rad. I just installed a 4 row aluminum rad, fresh antifreeze and purple ice. I am going to send in the 3 row and have it cleaned and keep it as a spare. I idled the car for awhile and when I turned it off the rad boiled into the recovery tank (with the 3 row rad). Tomorrow I plan on hooking up testing equipment and that way I will know what is going on with this problem. The shroud is correct and the blade half way in the shroud.
     
  7. 1972Mach1

    1972Mach1 Just some M.M.O.G. guy.....

    Yep, going to want to check the upper radiator hose vs the lower next. If the bottom is cold and the upper is hot, you've probably got a thermostat issue.
     
  8. blue suncoupe

    blue suncoupe Well-Known Member

    I think the issue was the 3 core rad being partly blocked. I will find out tomorrow. So you think just leave the 7 blade on? But, just when I think I know everything something throws a wrench into it. Engine overheating can be a challenge to diagnose but, I like that.
     
  9. Dr. Roger

    Dr. Roger Stock enthusiast

    I had an old 3-core brass/copper radiator that only overheated when the temp got above 90 F outside but cooled just fine the rest of the year. Replaced it with a new aluminum one and it has never overheated, even well over 100F outside. Old radiator was pretty clogged, and it had a about 10% of the cores blocked off by someone due to a bad leak at some point in its distinguished career.
     
  10. blue suncoupe

    blue suncoupe Well-Known Member

    Glad to hear that you got it solved. It was 93 F that day but, I would like to drive it no matter the temp. I think this new 4 core will work out too.
     
  11. yachtsmanbill

    yachtsmanbill Well-Known Member

    I tend to blame a lot of stuff on the fan clutch. If its "locked" at speed, it takes a ton of horsepower (heat) to turn any fan. When you shut it off the fan should roll maybe 4 turns then stop.

    I just installed a cut down 7 blade fan by 2 inches on the OD, new 3 core aluminum rad, no shroud, and a new T stat with a fresh built 465CI 455 (+.040") and it NEVER runs over 170F. A simple IR gun will pinpoint whats going on. I installed 2 NEW T stats, (chinese of course!!) and they were both bad. The 3rd was good and cured all the ills.

    The last one is the distributor advance. Is it running retarded? Thatll boil the pimples off a blistered pussy in a pepper patch faster than a microwave! ws
     
    Waterboy likes this.
  12. blue suncoupe

    blue suncoupe Well-Known Member

    The fan clutch works fine and the T stat is good(165) MSD dist all set. I think it was just the rad. Find out tomorrow baring any rain.
     
  13. copperheadgs1

    copperheadgs1 copperheadgs1

    That 7 blade 20” fan is not correct for a 72 455 Riviera or otherwise. Show a picture of it. The 5 blade 20” is correct for 71-72 and probably later 455’s. All cars across the model line would have used that fan when car had AC or heavy duty cooling or all Stage-1. Don’t overlook the fan clutch. Make sure it is thermostatic. Real curious what that big 7 blade came from?
     
  14. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    A 4 core aluminum radiator is a waste of money. I have been warning guys about that for some time now. Can't remember if you were one of them, you seem to have more than one thread going about the same problem.

    Bill, if a fan turns 4 times after shut down, the clutch is bad, it's free wheeling.
     
  15. blue suncoupe

    blue suncoupe Well-Known Member

    The car had a 350 & I got a 455 from a Riviera, had it rebuilt & installed it. (That is the 20"7 blade fan??) I know that the 1972 skylark 455 with A/C was equipped with a 20" 5 blade not sure how much that factors into it. I have read that the 20" 7 blade will move more air? If the 20"5 blade moves more air I will post for one on V8 Buick, otherwise I will leave the 20" 7 blade on it. I am mistaken on the 1972 Riv fan I thought it was the 20" 7 blade that I have on the car but, the 1972 Riv wa equipped with a 18" 7 blade with or without A/C. So where did this 20" 7 blade come from??
     
    Last edited: Jul 21, 2019
  16. yachtsmanbill

    yachtsmanbill Well-Known Member

    If a fan turns 4 times after shut down, the clutch is bad, it's free wheeling.

    Maybe not 4 turns (maybe 4 blades?) but not an instant stop either. Once up to speed (engine speed) it should run at a constant RPM like lets say for grins, 1500. After that the fans make so much noise and take a bunch of kilowatts to turn, that the solution was to slow them down via the clutch. Thats my take on it anyway. Had a '74 455 Toronado (in 1978) with a bad non slipping clutch and it would overheat at anything over 50 mph. A new clutch remedied that problem.

    As far as 5 vs 7 fan blades are concerned, a visual interpretation with a smoke bomb will tell you which moves more air. Let yer eyes be the judge. ws
     
  17. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The non thermal ones react to RPM. They let the fan turn slower at higher RPM like when you are on the highway and don't need the fan. That saves power. The thermal ones react to temperature and turn the fan closer to direct drive when hot air hits the coil. Neither clutch should free wheel. When they do, there is no clutch action at all, which is no bueno.:)
     
  18. Dr. Roger

    Dr. Roger Stock enthusiast

    According to my 71 manual, "air-conditioned and heavy duty cars are equipped with an 18-inch, 7-blade fan (350 cu. in.) or a 20-inch 5-blade fan (455 cu. in.).
     
  19. blue suncoupe

    blue suncoupe Well-Known Member

    You are correct ! My 72 manual states that also I have decided to install the correct 20" 5 blade fan. I thought that the Riviera blade would cool better but, I will install what GM say's is correct. Anyone got one?
     
  20. copperheadgs1

    copperheadgs1 copperheadgs1

    That’s what I have been saying all along.
     

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