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1968 Overheating

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  • Rolly Carlson

    1968 Overheating

    I have a 1968 427/390 that overheats. So far I have

    replaced the termostat
    run it without a termostat
    made sure the water pump is working
    replaced the radiator cap
    made sure it was completely full of coolant
    tried Wetter Water
    replaced the radiator (the car sat for 32 years so I thought it could plugged)
    removed the fan and clutch and replaced it with a flex fan and spacer

    Some of these things have helped but it still overheats when it's above 80 degrees and it's driven below 40. It cools down some on the highway but eventually gets to hot. The car has had a body off restore and most of the parts are original. I'm trying to keep it that way. I'm not happy with the new radiator and fan. I'm out of ideas except for another heavy duty radiator with front mounted blower fans. Any other ideas?
  • Robert S.
    Very Frequent User
    • July 31, 2004
    • 377

    #2
    Re: 1968 Overheating

    Seems to me you have done everything correct thus far. Except as you said "replaced the radiator (the car sat for 32 years so I thought it could plugged)" I would bet there is a far amount of gunk/rust built-up in the engine water-jackets too from sitting so long. Did you reverse flush the the system as well? That might loosen up some of the stuff in the engine, just hope it doesn't block other passages.

    Do you have the correct fan, shroud and especially the radiator seals?

    One other option for you to try is a high volume water pump. Check JEGS or Summit for what is available for your car.
    Bob

    Comment

    • Rolly Carlson

      #3
      Re: 1968 Overheating

      Thanks for the response. The engine was totally rebuilt at the time of restore, so it should be free from all gunk. Only around 500 miles on it. Yes, I do have all the orginal equipment and will put what I can back on. But, I'm afraid It's going to take some aftermarket 'stuff' to fix it. I'll look in Jegs.

      Comment

      • Wayne P.
        Extremely Frequent Poster
        • August 31, 1975
        • 1025

        #4
        Re: 1968 Overheating

        Don't forget to make sure the timing and advance are correct.

        Comment

        • Mark #28455

          #5
          Don't buy non-stock stuff yet

          I own several BB cars and they ALL run totally stock cooling systems - and work OK. That includes my 489 cu in L89.

          You have to remember that the oval port engines were totally streetable and were factory designed for reliable day to day use. You are missing something!

          Is the fuel/air mixture correct? Is there a vacuum leak? Is the exhaust heat riser valve opening? Is the ignition advance working? Is the timing correct - both initial and total? Is the vacuum advance working and attached to manifold, not ported vacuum? Has the engine been "hot rodded" or is it stock? Are all the radiator/fan shroud seals intact? Is the fan shroud intact? Is the spoiler under the nose of the car intact? Etc.

          Once you find the glitch, it will work fine.

          Mark

          Comment

          • Clem Z.
            Expired
            • January 1, 2006
            • 9427

            #6
            was not there a call back on 68s to cut open

            the front of the car for more air,was that done?.

            Comment

            • Terry F.
              Expired
              • September 30, 1992
              • 2061

              #7
              Re: 1968 Overheating

              Rolly,
              It is possible that the engine has a head gasket leak. Compression that pushes past the head gasket and into the water jacket will make it look like it is over heating. You can watch for air bubble in the radiator when the engine is running and warmed up. I would take the radiator cap off when cool and run it untill it gets hot. Watch the water/antifreeze in the tank for continuous bubbles. You will need to make sure it is fairly full so you can see the bubbles. Just a possibility depending on the condition of the deck surface and type of head gaskets used. Seen it before. Terry

              Comment

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

                #8
                Re: was not there a call back on 68s to cut open

                Clem,

                I remember the TSB that GM sent on the over heating problem and the modification that you mentioned. I don't know much about C3 but seems I remember some early C3's originally had no holes in the lower front panel? The TSB included templets used to cut the rectangular shaped holes.

                Comment

                • Terry F.
                  Expired
                  • September 30, 1992
                  • 2061

                  #9
                  Yes, early cars were recalled to have the

                  front valence panel cut open to improve air flow. Not sure if it was an actual recall or not. I also read that the front end would get light at high speeds and this would help that a bit also?? I have the templates for the cut-outs that were issued back then in a dealer tech bulletin. Take care, Terry

                  Comment

                  • Terry F.
                    Expired
                    • September 30, 1992
                    • 2061

                    #10
                    Re: 1968 Overheating

                    Rolly,
                    Does your car have its original lift brackets still in place? If so, any chance you could send pictures of them or tell me what part numbers and marking are on them? Thanks, Terry

                    Comment

                    • Terry F.
                      Expired
                      • September 30, 1992
                      • 2061

                      #11
                      Re: 1968 Overheating

                      The problem with a seeping head gasket is that it may not leak untill the engine is fully warmed up. So, it can be a pain to catch. Thereb have been a lot of suggestions made that are good. Each system needs to be in place. I have an original 390hp. If you need a picture of something, let me know. Terry

                      Comment

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

                        #12
                        Re: 1968 Overheating

                        Rolly,

                        I may be completely wrong on this but I seem to remember the first engine lift brackets coming in on the new 69 models? Could it be that big block had these in 68 but not small block? My new 68 Z28 Camaro definitely did not have the lift brackets when delivered. In fact, I vividly remember scrounging a set for my 68 from a replaced complete warranty engine assembly from a new 69.

                        Comment

                        • Jack H.
                          Extremely Frequent Poster
                          • April 1, 1990
                          • 9906

                          #13
                          Before you go too far...

                          DEFINE 'overheat'. If it's not popping the rad cap and spewing coolant while you're driving, you may NOT have a case of bona fide overheating. Many simply see the cockpit temp gauge reading higher than they believe to be safe and then declare their car is 'overheating'...

                          There are MANY prior threads in the archives that address the inaccuracy of the temp guage with suggestions on how to approach the issue. Basically, you start by getting a 'second opinion' of the actual temperature of the engine coolant (use an external IR thermometer, duct tape wrap a meat thermometer onto the upper rad hose, Etc.) and compare that to the reading shown on the temp gauge.

                          Lots of folks have 'chased their tails' believing the dash guage was accurate when it wasn't!

                          Comment

                          • Terry F.
                            Expired
                            • September 30, 1992
                            • 2061

                            #14
                            Re: 1968 Overheating

                            For the most part I believe the engines had the lift brackets on them. It is possible that some dealers removed them when the car arrived as part of the dealer prep. I have pictures of several 68 corvettes with them but the pictures don't shoe the details like part number and symbols and small holes. The forward bracket on some big blocks had a small hole drilled through it. Looked like a throttle spring might have attached there?? Terry

                            Comment

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

                              #15
                              Re: 1968 Overheating

                              I suppose it's possible that the brackets may have been a mid 68 addition and early cars had no brackets? (my new 68 was a December 67 build) Also, could it be that big block started using these before small block?

                              The brackets would have had nothing to do with new car delivery, or "prep", so if they were installed at Flint/Tonawanda, they remained on the car.

                              Comment

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