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  • Thanks TSB. I'm not sure that is the answer however. I had about 120 miles of normal operation and rock solid steady temps. There is plenty of coolant in the overflow and the radiatior is full to the top. Not sure how I can check for a bubble. Any ideas on that?

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    Last edited by 74NovaMan; April 26th, 2015, 07:15 AM.
    Chris - HRPT Long Haul 03, 04, 05, 13, 14, 15,16 & 18
    74 Nova Project
    66 Mustang GT Project

    92 Camaro RS Convertible Project
    79 Chevy Truck Project
    1956 Cadillac Project

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    • Is that a picture while running? If the temps are pogo'ing between 160 and 220+ in a short period of time, that screems to me low on coolant. If it took ten minutes to go from 220+ down to 160, then that's a different story. When you overheat, it goes over 220 (or pick your number) and stays there for tens of minutes at a time, or for a good half hour with the engine off.
      Escaped on a technicality.

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      • That pic is when cold. The temp seemed to creep up over a couple of minutes and when it dropped it went very quickly and was about 20-30 degrees below normal and seemed to hold there. I'm not honestly sure it is getting that warm based on the rapid cooldown. I am starting to suspect the guage but i would not think that it would shoot up like that in a failure.
        Chris - HRPT Long Haul 03, 04, 05, 13, 14, 15,16 & 18
        74 Nova Project
        66 Mustang GT Project

        92 Camaro RS Convertible Project
        79 Chevy Truck Project
        1956 Cadillac Project

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        • Not the gauge. What happens is a steam pocket forms and the steam is at 212+ as it's easy to heat steam, hard to heat water/coolant, also steam is a poor conductor of heat, so it's against the thermostat too, but slowly heating it enough to open. Once it opens though the water pump can pull the cold water from the radiator in, which pushes the steam out to the radiator and the temp sensor get's hit with cold water as does the thermostat that then slams shut and the process repeats.

          I'd top off the coolant with the heater hose removed, then fire up the car with the cap off and watch the coolant level in the radiator. It'll probably spill over right around the time the thermostat opens, but then the coolant level will drop like a rock. At that point you have to be fast to fill the radiator. It's a good practice to leave the level an inch or two below the fill neck, it keeps it from spilling or blowing into the overflow bottle more often. I've had good luck with the heater hose removed method, and the coolant level NOT dropping like a rock but very clear when hot water was starting to enter and flow fast through the radiator. Usually only drops an inch or two then.

          Follow up check is on the functionality of the radiator cap. If it's weak it'll allow the steam pockets to form more easily versus having pressure to keep the coolant in liquid form.
          Last edited by TheSilverBuick; May 21st, 2013, 12:53 PM.
          Escaped on a technicality.

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          • Any thoughts on why it would not do that for 120 miles and start now?
            Chris - HRPT Long Haul 03, 04, 05, 13, 14, 15,16 & 18
            74 Nova Project
            66 Mustang GT Project

            92 Camaro RS Convertible Project
            79 Chevy Truck Project
            1956 Cadillac Project

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            • Different driving pattern? Highway driving? Staying above idle rpm keeps the water pump moving the water more efficiently and the system under more pressure to keep the steam at bay and the coolant higher up (against the sensor and thermostat). Stop and go will start and/or aggravate the oscillation and continuous rpm/speed will dampen it and make it go away over a couple miles.

              I don't know if you have a heater control valve or not, simply using versus not using the heater could of done it if you have a valve.

              A possible leak in the system some where?

              And lastly, IMO, 120 miles isn't much driving time, especially around town driving where it never really heats up.
              Escaped on a technicality.

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              • I'm open to hear other ideas, but I really doubt it's the thermostat and even less so the temperature gauge. When thermostat's fail, you either get really really hot and no cool down or the engine simply does not warm up.
                Last edited by TheSilverBuick; May 21st, 2013, 01:07 PM.
                Escaped on a technicality.

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                • Thanks for the ideas. I had a good mix of driving in town and freeway. I don't seem to be losing coolant anywhere. I did check for heat when it was reading hot and that seemed fine. I'll try heating it up to temp with the cap off and see what happens.
                  Chris - HRPT Long Haul 03, 04, 05, 13, 14, 15,16 & 18
                  74 Nova Project
                  66 Mustang GT Project

                  92 Camaro RS Convertible Project
                  79 Chevy Truck Project
                  1956 Cadillac Project

                  Comment


                  • Fan clutch failing? Had a 231 in a '78 Buick Regal do that once......
                    Of all the paths you take in life - make sure a few of them are dirt.

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                    • No fan clutch. Maybe I should get one?
                      Chris - HRPT Long Haul 03, 04, 05, 13, 14, 15,16 & 18
                      74 Nova Project
                      66 Mustang GT Project

                      92 Camaro RS Convertible Project
                      79 Chevy Truck Project
                      1956 Cadillac Project

                      Comment


                      • Only if you are chasing MPG or reducing engine noise. I personally like things simple - never much cared for clutch fans.

                        Is your fan a solid or a flex? Looks like a flex from the picture?
                        Last edited by STINEY; May 21st, 2013, 01:18 PM.
                        Of all the paths you take in life - make sure a few of them are dirt.

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                        • Flex
                          Chris - HRPT Long Haul 03, 04, 05, 13, 14, 15,16 & 18
                          74 Nova Project
                          66 Mustang GT Project

                          92 Camaro RS Convertible Project
                          79 Chevy Truck Project
                          1956 Cadillac Project

                          Comment


                          • I remember some flex's getting a bad rap for performance.....maybe you have one of those?
                            Of all the paths you take in life - make sure a few of them are dirt.

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                            • It has worked fairly well in the past. It has got to be the thermostat or an air bubble.

                              Thanks for the ideas guys.
                              Last edited by 74NovaMan; May 21st, 2013, 01:53 PM.
                              Chris - HRPT Long Haul 03, 04, 05, 13, 14, 15,16 & 18
                              74 Nova Project
                              66 Mustang GT Project

                              92 Camaro RS Convertible Project
                              79 Chevy Truck Project
                              1956 Cadillac Project

                              Comment


                              • I don't believe a fan can cause rapid temperature oscillations. Either slowly heat up or slowly cool down over a period of a few minutes.
                                Escaped on a technicality.

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