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  • Head gasket?

    This is my first engine build, and I've had a few issues. The final issue might be head gasket, but I'd like some guidance. The car is a 1999 Miata with a few bolt-ons.

    When at the track or autocross, I loose some coolant, about a half gallon per day. It doesn't seem to be leaking anywhere under the motor. The exhaust, just headers to straight pipe, does seem to leave some condensation on the ground when running.

    I'm doing a pressure test right now. It took about an hour for it to go from 16 to 15 psi. Seems to be holding at 15.

    So, do I do the head gasket now? Should I just shut up and drive?

    Thanks all!

  • #2
    Check the heater hose clamps. The one on the back of the head (hardest to reach) is often the culprit. Often these hoses will leak vapor when hot if the clamps are bad or not sufficiently tight. Check all the other clamps as well. Many times all will be fine when the car is cold but they will have a slight leak when hot. Since it is vapor and not dripping liquid this can be very hard to find.

    If you run the car with the cap off the radiator are there bubbles in the fluid when the car is running? That would indicate a possible hg issue. If water shoots out of the radiator with the car running for sure you have a hg issue.

    You can use a combustion gas tester to check the radiator fluid for evidence of combustion gas that would indicate a hg issue. UV leak detection is also a good tool for things like this.

    I'd be surprised if it were the hg. My money is on a pinhole leak or bad clamps somewhere.

    BTW - after a finding a aftermarket 'Miata' head gasket with some water and oil passages blocked off (can you say 'instant blown motor'?) I now use only Felpro or Mazda OEM head gaskets.

    Mark


    Originally posted by mdotmurphy View Post
    This is my first engine build, and I've had a few issues. The final issue might be head gasket, but I'd like some guidance. The car is a 1999 Miata with a few bolt-ons.

    When at the track or autocross, I loose some coolant, about a half gallon per day. It doesn't seem to be leaking anywhere under the motor. The exhaust, just headers to straight pipe, does seem to leave some condensation on the ground when running.

    I'm doing a pressure test right now. It took about an hour for it to go from 16 to 15 psi. Seems to be holding at 15.

    So, do I do the head gasket now? Should I just shut up and drive?

    Thanks all!
    AiM Data and Video systems, Suspension Setup, Race car builds, support, and rentals. At your beck and call.

    Mark Nichols
    Iron Canyon Motorsports
    http://www.ironcanyonmotorsports.com

    Comment


    • #3
      Thanks for the additional tests. I've got a felpro ready to go, if it comes to that.

      Comment


      • #4
        Originally posted by markn View Post
        Check the heater hose clamps. The one on the back of the head (hardest to reach) is often the culprit. Often these hoses will leak vapor when hot if the clamps are bad or not sufficiently tight. Check all the other clamps as well. Many times all will be fine when the car is cold but they will have a slight leak when hot. Since it is vapor and not dripping liquid this can be very hard to find.

        If you run the car with the cap off the radiator are there bubbles in the fluid when the car is running? That would indicate a possible hg issue. If water shoots out of the radiator with the car running for sure you have a hg issue.

        You can use a combustion gas tester to check the radiator fluid for evidence of combustion gas that would indicate a hg issue. UV leak detection is also a good tool for things like this.

        I'd be surprised if it were the hg. My money is on a pinhole leak or bad clamps somewhere.

        BTW - after a finding a aftermarket 'Miata' head gasket with some water and oil passages blocked off (can you say 'instant blown motor'?) I now use only Felpro or Mazda OEM head gaskets.

        Mark
        I just saw this happen at the track last month. It's definitely worth investigating. You should be able to see signs of leakage in this area if the clamps are loose or there's a split hose. they'll often split right where the nipple terminates inside them.
        www.TrackHQ.com

        Comment


        • #5
          A leak down tester can also tell you if you have a HG issue amongst other things. ~$30 cheapo tester from HF + modding it with a $7 100PSI gauge from amazon at least gets you in the ballpark for finding a lot of potential problems.

          If you're able to get behind the head, replace the "cursed" water plug at the same time as the hose clamp and/or hoses. cheap insurance.

          Comment


          • #6
            The rule is "test" before teardown.

            If you want to find out now leakdown and compression test.

            If not in a hurry send a coolant sample to Blackstone Labs and they will tell you if combustion gases are in the coolant.

            If there are no gasses in the coolant you then can leak the motor down and compression test to find out where your power loss is.

            Comment


            • #7
              An often over looked idem. But if all of the above test checkout. Also test the radiator cap. I've seen those leak or not hold pressure. Push out coolant so slow you don't really see it, till it's gone.
              That's not a Typo, I just can't spell no so well.

              Comment


              • #8
                Dammit Gian. That is too obvious. Diagnosing engine issues is a black art. Don't be giving anything away.

                Seriously though, good call on the cap. I completely forgot about that in spite of the many times I've run into it. Sometimes a quick squeeze with a set of pliers on the tangs of the cap is all that is required.

                Mark

                Originally posted by Gian View Post
                An often over looked idem. But if all of the above test checkout. Also test the radiator cap. I've seen those leak or not hold pressure. Push out coolant so slow you don't really see it, till it's gone.
                AiM Data and Video systems, Suspension Setup, Race car builds, support, and rentals. At your beck and call.

                Mark Nichols
                Iron Canyon Motorsports
                http://www.ironcanyonmotorsports.com

                Comment


                • #9
                  Thanks, I found some great info on testing. I picked up the 'exhaust in the coolant' tester, and will get a leak down tester soon.

                  I don't have any results yet, because real job.

                  Comment


                  • #10
                    Update: tested with exhaust gas detector. It just barely turned green. I went ahead and put in the mls gasket.

                    Now no more condensation from tail pipe. Holds coolant pressure.

                    Thanks again for all the testing info.

                    Comment

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