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Cooling Fan & Shroud

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by 70K5Jimmy, Jun 3, 2001.

  1. 70K5Jimmy

    70K5Jimmy Registered Member

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    I've got a 454 stuffed into my 70 K5 by the previous owner. It has the original 4 row radiator and long water pump but no fan shroud. I'm about ready to fire this thing up but the 19 1/2" fan is toast. Here's the questions --
    How big a fan does this need?
    Original clutch type, flex fan or electric fans against the grill?
    If belt driven fan, what shroud will match up, the original for K5 350, the one for 396/402BB or the one for 74 p/u engine came off?

    Not a lot of junk yards around here so its hard to find this stuff out first hand.
     
  2. RingMaster4x4

    RingMaster4x4 1/2 ton status Premium Member

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    I just put a 427 tall block in my 72 blazer and I am using one 16" electric fan. The motor runs cooler than my 350 ever did.

    If you build it, the mud will fly!
    72 K5 blazer 1 ton with a 427 tall deck and TH350/NP205 and 12"of lift with 40"tires.
     
  3. JST12

    JST12 1/2 ton status

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    From what the Flex-a-lite info says, you need a CFM rating based on HP of your motor, and whether or not you run AC. Seems like most good 16 in electric fans get you about 2500 CFM which is good for cooling up to 250 HP without AC and 225 HP with AC. There is a dual set-up (Model 250,260) with up to 5200 CFM but it needs a 34 inch wide radiator. I have long water pump too and a body lift, so it's a hassle to get belt driven fan in and to center the shroud. I'm getting a smaller dual set-up ( Flex-a-lite 210) because the radiator is only 28 inches wide. It has a 2600 cfm rating. Hope it's enough. JT
     
  4. Burt4x4

    Burt4x4 3/4 ton status

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    Duno about you BBC guys but my 350 w/3row stays nice and cool with just a Flex-A-Lite BlackMagic M150 rated at 2800cfm. Great fan it has allways been able to keep my mildly built 350 under 200 in 100+deg weather. I carry a flex fan for the trail just incase my electric desides to go on vacation[​IMG]...

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
    <A target="_blank" HREF=http://www.burt4x4.coloradok5.com>http://www.burt4x4.coloradok5.com</A>
     
  5. Steve_Chin

    Steve_Chin 1/2 ton status

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    I'm running a Rodney Red aluminum radiator (custom built to original radiator dimensions, 2-row) with a stock 19" fan and the stock '72 fan shroud. I am using a Hayden heavy-duty thermal fan clutch instead of the crappy viscous coupling that was stock on the Blazer. BIG difference in cooling potential and reliability. FWIW, the water temperature gauge never leaves the top of the cold range during normal operation and when I'm really banging on it, it doesn't get more than a needle width into the normal operating range.
     
  6. 70K5Jimmy

    70K5Jimmy Registered Member

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    Re: Thanks

    Thanks for the responses. Nothing beats hearing from people who wrench on the same kinds of rides. BTW It came with a 3" body lift, rather put on a suspension lift but I guess there's some problems with the HEI distributor fitting... the lift doesn't appear to change the center line of the fan to radiator, but I can't tell for sure. Hate to go through the time and $ ordering parts and returning them till I got it right. Even with the BB there's still 6 1/2" from the water pump pulley to the radiator - too far to just eliminate a shroud, I think. Maybe the solution is a combination of all your suggestions: clutch fan with say a 12" electrical fan instead of shroud? Any comments?

    Thanks again.
     
  7. Dan71gmc

    Dan71gmc Registered Member

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    Re: Thanks

    If you do use a belt driven fan and shroud, rule of thumb is "The shroud shoud not come back any farther than to cover 1/2 of the fan blades", to get the proper air flow. Have always used that and never had any serious overheating under normal to heavy towing conditions.
     
  8. travis

    travis 1/2 ton status

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    It may take a few driveline mods, but have you considered moving the engine forward 2"? You will see extra holes drilled in the frame for the crossmember. I guess 2WDs came with the engine mounted farther forward. I'm sure you will have to drill new holes for the xfer case crossmember and L-bracket. Front and rear driveshafts will also need to be re-fitted. Sounds like a lot of work, but if you really want to get rid of the body lift it may be an option.

    Travis
     

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