Fan Clutch Adjustment for 1965 small block - NCRS Discussion Boards

Fan Clutch Adjustment for 1965 small block

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  • Mark P.
    Very Frequent User
    • May 13, 2008
    • 941

    Fan Clutch Adjustment for 1965 small block

    I am concerned about running hot at idle with my recently rebuilt L-79 engine that has had its initial break-in but has not yet been driven to complete the break-in.

    After about 30 minutes idling during an 80 F day the temperature gauge was reading about 195F and my IR gun was reading 210F on the thermostat housing.

    My fan clutch was purchased from thepartsladi on EBAY and was listed for 1960-1970 Corvettes and is a reproduction of the 3916141 R service replacement fan clutch .

    This 1990 article states that the fan clutch is likely operating at a maximum friction of 210F (for 1968 and later Corvettes) and should be about 190F for 1967 and earlier Corvettes.

    Since this article is now 35 years old I thought it would be a good idea to check if members still recommend this adjustment.

    For my fan I plan to rotate the spring counter clockwise 180 degrees and set it into the opposite slot. Is this correct ?

    Also, I noticed that the CC version has hot glue where the spring drops into the slot. Do you think this is just for shipping ?

    Attached Files
  • Mark E.
    Extremely Frequent Poster
    • April 1, 1993
    • 4599

    #2
    195 degrees after idling for 30 minutes in warm weather isn't a problem.

    What temperature thermostat is installed?
    Mark Edmondson
    Dallas, Texas
    Texas Chapter

    1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
    1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

    Comment

    • Jack M.
      Extremely Frequent Poster
      • March 1, 1991
      • 1176

      #3
      As Mark Edmondson has indicated, those temperature reading are well within the norms.
      This was a TSB regarding the 1965 temp gauge:
      Temp-Gauge-November-23-1965a.jpg
      Temp-Gauge-November-23-1965b.jpg


      For 1966 Corvettes, the owner's manual changed... reflecting the info from the TSB.
      (issued well AFTER 1966 production started)
      This was the initial 1966 owner's manual temp gauge text:ownman-6.jpg

      In the 2nd Edition 1966 owner's manual, text changed to the following:
      ownman-8.jpg

      BTW- The old PDF article you posted, was from a scan I made... ages ago.

      Comment

      • Mark F.
        Extremely Frequent Poster
        • July 31, 1998
        • 1567

        #4
        Mark P.

        In addition to what Mark E and Jack say:

        1. What psi rating is your radiator cap ?
        2. Are you losing any coolant ?


        Remember that properly functioning caps INCREASE the boiling point of water.
        Plus, if you have any kind of coolant additives, that helps increase the BP even more.
        As long as you don’t OVERFILL, even if the internal temp at the thermos housing is higher than the 195° EXTERNAL temp you measured, it's probably not a problem.

        Dewitt’s has a nice article discussing all of this…see link (and excerpt) below.

        https://www.dewitts.com/blogs/news/13852841-what-pressure-cap-rating-should-i-use?srsltid=AfmBOopr7YxOYPmpWMWlLP915Kw5eO7WzZ0pDx NuNag_u87P-oheGFo_

        …A standard coolant mixture of 50 percent water and 50 percent ethylene glycol (such as our own DeWitts High Performance Coolant has a boiling point of 223 degrees. A cooling system using a 15 psi radiator cap will add 45 degrees to the boiling point for a final boiling point of 268 degrees…

        There’s more, too…

        268° is higher than Jack's 250°
        GM TSB cutoff, but I think you'll get the drift...
        thx,
        Mark

        Comment

        • Larry M.
          Extremely Frequent Poster
          • January 1, 1992
          • 2701

          #5

          You can also add the engine cooling enhancements that were installed for the factory air cars.........unless you are getting car judged. These should help to keep the engine temperatures down. DE REDUILD should still sell all the necessary pieces needed.

          Larry

          Comment

          • Mark P.
            Very Frequent User
            • May 13, 2008
            • 941

            #6
            Hi Larry - after I take it through judging I will look into the A/C cooling enhancements.

            Hi Jack - thank you for the TSB. I wonder how many 66 gauges were installed in 65 cars to make owners feel more comfortable. Did you ever adjust your fan clutch as suggested by the article ?

            Hi Mark E - I have a 180F thermostat.

            Hi Mark F - I have a 13lb new cap on my expansion tank. I never lost coolant through the overflow but I did find a leak with the upper radiator hose and reinstalled the hose with The Right Stuff RTV. It seemed to run cooler after doing that. The temperature reading off the thermostat housing was 193 after about 15 min of running it.

            Comment

            • Jack M.
              Extremely Frequent Poster
              • March 1, 1991
              • 1176

              #7
              Originally posted by Mark Pellowski (49021)
              Did you ever adjust your fan clutch as suggested by the article ?
              Mark- Back in the 90's, I did reclock my spring... there may have been a slight difference in temps, but nothing significant for me (no IR gun back then). In years following, I recall reading an article (from someone in the business) that refuted the claim of that procedure being beneficial... so I no longer posted and/or recommended that article.

              As usual, your mileage may vary...

              Comment

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