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Help with overheating

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  • Bill Richards

    Help with overheating

    My 66 SB has an overheating problem. When driving in temperatures around 50 to 60 degrees the car runs at about 160 to 170 until I start to climb a pass, then the temp. starts climbing up to around 200. When driving in warmer temps. the car gradualy gets hotter and hotter up to 250, until I shut it down. It is not boiling over at this point because of my antifreeze mix, about 70-30, antifreeze to water. I have a 160 degree thermo. that is working properly. A new water pump and fan clutch. The timming is at 6 degrees and the motor is not running in a lean condition. I have no idea what has been done to the motor in the past. It is a 300 hp, 327, and it uses no oil. Any ideas.
    Thanks, Bill
  • Duke W.
    Beyond Control Poster
    • January 1, 1993
    • 15610

    #2
    Re: Help with overheating

    Radiator specs and age?

    Vacuum can ID no.? Does it meet specs?

    The higher the concentration of antifreeze the lower the heat capacity of the coolant; 70 percent is the upper limit of the OE recommended concentration, but if the cooling system and ignition map are to spec, it should not be the problem.

    I usually shoot for a 50-55 percent antifreeze concentration.

    You should take an manifold vacuum @ idle speed reading, which will help determine if a high overlap cam has been installed. If so, the OE spec vacuum can may not be properly matched to engine vacuum characteristics, which is a common cause of high coolant temps.

    Duke

    Comment

    • Michael H.
      Expired
      • January 29, 2008
      • 7477

      #3
      Re: Help with overheating

      Bill,

      It sounds as if your radiator isn't doing it's job. If your not loosing coolant and don't have vacuum leaks or have some other mechanical problem, the radiator is certainly suspect. Is it original, or at least very old?

      Comment

      • Gerard F.
        Extremely Frequent Poster
        • June 30, 2004
        • 3803

        #4
        Re: Help with overheating

        Have you checked for vacuum leaks (carb, base gasket,other leaks). Something could be leaning out your mixture under load, or your secondaries maybe are opening with no or reduced fuel flow.

        Just a thought. But it does sound carb related.

        Jerry Fuccillo
        #42179
        Jerry Fuccillo
        1967 327/300 Convertible since 1968

        Comment

        • Joe C.
          Expired
          • August 31, 1999
          • 4598

          #5
          Re: Help with overheating

          Bill:

          The original radiator, even when brand new, was not overdesigned with very much margin for error. The slightest deterioration, with time and scale buildup, will cause the radiator to be marginal, at best. If you run hot, at speed, then that sounds like a radiator capacity issue. Other factors, such as vacuum advance, and fan clutch operation should have little effect as long as the car is moving and the engine is under load. As mentioned earlier, a 50-50 mix will transfer heat somewhat better than your 70-30 mix. Also, the 160 thermostat will have no effect on the upper limit of your engines operating temp, but will only affect the lower limit when operating in very cold ambient temps. Change back to a good quality 180 degree stat, like Robertshaw, Stant, or the like.

          oe

          Comment

          • Rick #42561

            #6
            Re: Help with overheating

            Are there any other signs of overheating?

            Could the gauge or sending unit be malfunctioning?

            Comment

            • David M.
              Very Frequent User
              • September 30, 2004
              • 515

              #7
              Re: Help with overheating

              Dont forget about the radiator support gaskets/seals. You do have the rad fan shroud intact? Check for lower rad hose collapse. Try a 190* T-stat, even 195* see what that does. Simple stuff first. Changing from 160 to 180 didnt help me. I changed to 195 cured my problem when going up the hills to Lake Tahoe, big block car. Water Wetter works well too. If freezing isnt a concern where you live go even lignter on the mix 40 coolant 60 h2o. Above all as others stated the radiator core must be clean and free of scale and obstruction or everything else will be a bandaid.

              Comment

              • Joe C.
                Expired
                • August 31, 1999
                • 4598

                #8
                Re: Help with overheating

                Rick:

                The entire discussion assumes that your temp gauge readings are fairly accurate. That is another entire subject in itself. Get yourself an infrared temp measuring device and read the temp of the thermostat housing. Further, the temp gauge is by NO MEANS linear, even if it is properly calibrated at, say, 180 degrees. You must take readings at different temps, and compare to gauge readings. The gauge can be calibrated by wiring in a "t*******" resistor.

                You should NOT NEED the radiator shroud rubber seals (used after 1965) unless you have a 427, and/or air conditioning.

                A 195 degree, 180 degree, 160 degree, or ABSENT thermostat will not give your radiator more cooling capacity. Different variants will only make the engine operate at different temps during cold weather, and will affect warmup time. The only time that a thermostat change cures an overtemp problem, is if the replaced thermostat was not opening fully, and the new one is.

                Joe

                Comment

                • Michael H.
                  Expired
                  • January 29, 2008
                  • 7477

                  #9
                  Re: Help with overheating

                  Joe,

                  I'm glad you mentioned that the thermostat has little to do with engine run temps. (this oughta get a buncha replies) Several of the guys that cruise with me have also mentioned that you MUST have a thermostat in place to maintain a proper coolant temp. Without it, the coolant passes through the radiator too quickly to transfer heat into the coils. The opposing arguement is that, without a thermostat, the coolant also passes through the engine faster, picking up less heat per unit. (coolant volume) It does pick up less heat per unit but there are more units (more coolant flow) so it comes out even. The debate continued so... at the next car show, I drove the 22 miles to the event with a 180* stat in place. The ambient temp was aprox 85*. The highest temp reading was aprox 220* in traffic. One week later, I removed the stat completely and drove to the same show. The conditions were near the same with slightly higher ambient temp. The highest temp observed on the trip was 220*, the exact same thing as recorded with a thermostat.

                  That's nothing!! Wait till I tell you about the test with and without the vacuum advance connected. Coming soon. Still one more phase of the test to complete.

                  Comment

                  • Bill Richards

                    #10
                    Re: Help with overheating

                    Thanks for all the tips guys. I did check my temp with a ray gun and it was the same as the temp gauge in the car. Think I will reduce my mix to a 50/50 ratio. It looks as if this car has a replacement radiator. Would a back flush help? What hose would be used to back flush, top or bottom? Dont think I have an intake leak however the engine does have a noticable miss at 2000 rpm in park. Not sure why.
                    Thanks, Bill

                    Comment

                    • Rob A.
                      Expired
                      • December 1, 1991
                      • 2126

                      #11
                      Re: Help with overheating

                      Bill,

                      I realize you said the thermostat is working properly. Did you check it out of the car or in? If you checked it out, you might want to check its' operation installed by starting the engine cold, and feeling the upper radiator hose, which should warm up as the thermostat opens allowing H2O to return to the radiator. Good Luck...

                      Comment

                      • Bob R.
                        Extremely Frequent Poster
                        • June 30, 2002
                        • 1595

                        #12
                        Re: Help with overheating

                        You menntioned that you have a replacement radiator. Is it aluminum as the original? The aluminum radiator disapates heat better then a copper brass radiator.

                        Comment

                        • Gerard F.
                          Extremely Frequent Poster
                          • June 30, 2004
                          • 3803

                          #13
                          Check the carb

                          I think the guys are getting caught up on the radiator. I have a 67/327/300/3.08 with it's orginal radiator with 62K. Everything in the engine is original. The only overheating problems I've had, have been carb related.

                          Too lean jets or a vacuum leak, will give you overheating problems.

                          With a restored carb to stock specs, 160 degree thermo(which is stock), original distributor vacuum can, 17" vacuum at 650rpm idle, I rarely get over 200 degrees (and that's on a hill). Normally, I will cruise at under 180 in hot weather. Slow down in traffic and it goes to 200-210, and with the Vintage Air blasting.

                          The overheating problems which I've had in the past were all carb related, vacuum leaks at the base gasket or throttle bushings, undersized primary jets,and maybe also related to timing. Best thing to do is try to bring everything back to original stock. Maybe the previous owner changed the cam and screwed up everything.

                          Jerry Fuccillo
                          #42179
                          Jerry Fuccillo
                          1967 327/300 Convertible since 1968

                          Comment

                          • Gary #41345

                            #14
                            Re: Check the carb

                            Jerry, I have a vacuum leak under the carb perhaps the base gasket or adapter is warped, but I do run hot when idleing or slow run like a parade etc. I bring that up cause I was asked to use my 66 SB in a local parade and had to decline because for sure I would have overheated. I get a high pitch whistle at times from below the carb area and the actual cause is still underdetermined, I was close to changing everything a few times but when I tighten down the carb nuts it seems to go away for awhile then eventually it comes back to haunt me again. I replaced the gasket and would have changed the adapter but I think the last owner used cement to adhere it to the intake so I left it alone. Was going to change out the radiator but now that you say that leak could be the source of my overheating I'll take another look at that area. Thanks

                            Comment

                            • Duke W.
                              Beyond Control Poster
                              • January 1, 1993
                              • 15610

                              #15
                              Re: Check the carb

                              Check your AMA specs. The OE '67 thermostat begins to open at 177-183 (180 nominal), and thermostats typically aren't full open until 20-30 degrees above the initial opening point. (With AIR the thermostat was 195)

                              No one ever envisioned that these cars would still be in operating condition after 40 years.

                              Over time radiator tubes slowly build up deposits, which reduces heat transfer efficiency. There is no specific test to determine the loss of efficiency without testing the radiator in a laboratory, so if everything else in the cooling system is functional and the spark advance map is suitable for the engines vacuum characteristic, the last suspect standing is the radiator.

                              Nothwithstanding the above, operating temperatures of 210 or more may be considered "normal" under severe opeating conditions (stop and go traffic in hot weather, especially when using A/C), and with a 15 psi cap and 50 percent antifreeze concentration the boilover temperature is 265.

                              Duke

                              Comment

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