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Puzzling overheating

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  • #16
    spark advance

    Originally posted by bezhawk View Post
    If the timing is off, it will cause it to run hot too. Check the vacuum advance, the diaphragm can rupture without any visual clues.
    Just a technical discussion not a criticism. My understanding of the spark advance system is, the vacuum advance, aka spark modifier, is that it offers an advanced spark earlier at lower speeds and if it failed ie hole in diaphragm, there would be no advance at lower speeds and therefore the spark would remain somewhat retarded for the speed. I don't think this condition would cause overheating. The secondary level of advancement is the centrifugal weights and counter springs. There are two forces working against each other centrifugual ie the weights and the springs to counter the weights to control the amount of advance. If a spring is broken the remaining spring cannot counter the forces of the centrifugal weights and therfore an excessive advance condition is created, and therefore the excessive advance condition will cause overheating. This is my understanding Dave

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    • #17
      Originally posted by K Russell View Post
      Thank you for that part number. I can't find any other vendors who sell a sending unit for this engine. S.I. doesn't list it either but I'll call and hope.
      The engine isn't the issue because both the 6 and the 8 cylinder engines used the same guage, the guage/sending unit and voltage is. I don't recall reading anywhere in the posts the voltage of your system. If it is 12 volts and was originally 12 volts, and your existing sending is the 3/4 NPT, the 3/8 NPT could be used with 3/4 to 3/8 bushing.

      On your previous question regarding the exaust gases in the system without the loss of coolant, pressure from highest to lowest is the answer. The combustion gases are over 100 psi while the coolant pressure is maybe 8 to 12 psi. The gases can be forced into the cooling system while the coolant may never leak back past a bad gasket. I don't think you have a blown head gasket however as you lack other crucial symptoms of the diagnosis.

      The issue with the lower radiator hose is not its age but rather the existance of the anti-collapse spring. It needs to be there, new or not.

      I think you are on the right track though with the defective sending unit. Borrow the wifes cooking thermometer and carefully remove the radiator cap. Insert the thermometer and take a reading. Compare to inside temperature reading.

      Dave.

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      • #18
        Just a note that might only show up on 1 in a million. I got my 59 Lark and went through it, only because I had never had a six before, but to my surprise the head gasket was on backwards. Yes it can be done. If one does not read the direction on the gasket it's self. This puts a smaller hole in the wrong spot and inhibits the proper flow through the head. I didn't have any problem before but I had not put many miles on it. After owning it for almost ten years not it still has under 35K miles.

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        • #19
          Originally posted by altair View Post
          Just a technical discussion not a criticism. My understanding of the spark advance system is, the vacuum advance, aka spark modifier, is that it offers an advanced spark earlier at lower speeds and if it failed ie hole in diaphragm, there would be no advance at lower speeds and therefore the spark would remain somewhat retarded for the speed. I don't think this condition would cause overheating. The secondary level of advancement is the centrifugal weights and counter springs. There are two forces working against each other centrifugual ie the weights and the springs to counter the weights to control the amount of advance. If a spring is broken the remaining spring cannot counter the forces of the centrifugal weights and therfore an excessive advance condition is created, and therefore the excessive advance condition will cause overheating. This is my understanding Dave
          Excessive retarded timing can also cause overheating. I have seen many people set the timing with the advance hooked up. Since there is high vacuum @ idle, the advance does come into play. Take away the advance, and the timing will be set too slow. The centrifugal advance comes into play as the engine is at a higher rpm than when you set it.(the timing). It's easy to plot with a timing light and a tachometer.
          Bez Auto Alchemy
          573-318-8948
          http://bezautoalchemy.com


          "Don't believe every internet quote" Abe Lincoln

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          • #20
            Has anyone mentioned thermostat? I had a similar problem in my '53 Commander: it would get hot on the highway and then stay hot. Turned out to be a faulty thermostat!
            Joe Kresse

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