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Head Gasket or Radiator Cap

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  • Head Gasket or Radiator Cap

    Ok, so I know I can buy a new cap and see if it fixes it but...

    The coolant from my radiator is going into my overflow bottle and not sucking back in. I have no smoke out of my exhaust, yet... How can I tell if this is head gasket or radiator cap problem (can't suck coolant back into radiator)?

    Note coolant did come out of the breather hose once but it was in no way shooting out, unless it was and now it has gotten low it is failing to.

  • #2
    Sounds like rad cap.

    To Check for a head gasket, take the cap off when cold and fill right up with coolant, start the engine and look for little bubbles coming out, the odd bubble is alright but if you get something like a fizzy drink you have issues.
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    • #3
      also, run the engine then take the plugs out, if theres coolant on the tips of the plugs, its a head gasket


      • #4
        Fully sick advice, I'm on to it.


        • #5
          Milky oil or milky coolant is also another sign, usually much more extreme than the tiny bubbles.


          • #6
            you have an airlock there mate,system needs bleeding.
            rad cap off, heater on full, leave car running till operating temp , then see what the go is.......... it should bubble up per previous posts , then add coolant and wait for a while.

            Straightline2ten your motorcycle and motor car repairer for smash repairs

            insurance or private work, plastic welding,resprays, restoration and classics

            dianella 93703770


            • #7
              Hrmmm, my bike doesn't have a heater, only one passage for the coolant to go through. Air lock is highly possible since this may have been happening ever since I flushed my system not too long ago. I will take on your advice cheers.

              BTW Wasn't noticing bubbles. Temporary relief.


              • #8
                lol @ heater
                If cleanliness is next to godliness, why was jesus a dirty sandal-wearing beardo?


                • #9
                  If you have done a flush recently my money is on an air lock. Worth noting is some cars and bikes have bleed nipples at high points in the cooling system where air pockets settle, check your service manual to see if your bike has them. If it has them it’s just a matter opening them with the motor running till they pass water (letting the air out) and it should be sweet.

                  If the cap is more than a few years old I'd replace it anyway, they are cheap and a couple of things can go wrong with them that’s hard to pick.. Deformed rubber seals, spring that binds etc.. Also check the hose going from the cap to the overflow for splits or anywhere it can suck air rather than water back into the rad.

                  Oil in water/water in oil ... This is only when the things are real bad, for every 10 blown head gaskets I'd say only 1 (if that many) would have water and oil mixed.

                  What I would try..... From cold, take the cap off and run the bike and let it warm up.. If it has an air lock as it warms it will start to push out coolant, I wouldn't be surprised if it dumps a lot of liquid.. as the thermostat opens you will get a final gush of coolant followed by what sounds briefly like boiling (that your air lock coming thru the system) at this point start adding coolant "slowly" so it can mix in without dropping the temp too much (you want the thermo to stay open to let the air thru and out) until the system is full and hot (hoses going in and out of the motor should be about the same temp) then put your cap on and you should be done.

                  If your still having problem most radiator shops have a dye tester that sucks air from the cooling system thru liquid that will change colour when it picks up CO2 but these can be a bit hit and miss with small/intermittent head problems, but defiantly worth getting them give you a free test if your having no joy getting it sorted.

                  Let us know how you get on.

                  FWIW, I was a radiator fitter/repairer for 10yrs working on everything from small car heater rads thru to large earthmoving and mining rads.

                  Good Luck


                  • #10
                    I had a blockage on the thermostat bypass cause the same problem on a ZX6RR.

                    Like the others have said, radiator cap rubbers/seals might be the problem.

                    I tested the thermostat, but replaced it anyway.

                    Its easy enough to 'burp' the water system when doing these flush jobs.
                    Increasing my carbon footprint - one 500 @ a time...


                    • #11
                      I don't believe the ZZR has any sort of bleed nipple since the radiator cap is the highest point and my bike seems pretty simple in all respects. I let the thing heat up from cool with cap off, no real bubbles, coolant was slowly slowly leaking out the top. Did a little bubble thing periodically like every 5-8 seconds. Was getting real hot so capped it back up. I'm getting a new cap today, the radiator place near home said it is the same as a car radiator only they currently don't have any, they're all on order.

                      I'll let you know if a new cap solves all problems.


                      • #12
                        I wouldnt stick anything other than a genuine Kawasaki one on there - but thats just me.
                        Increasing my carbon footprint - one 500 @ a time...


                        • #13
                          just check to make sure its the same pressure rating
                          Respect is earned, not enforced.


                          • #14
                            Stick a 1.1 rated cap from superchreap or auto one on there.
                            Will be half the price of a genuine kawasaki cap.


                            • #15
                              Show it some love, get the genuine kawasaki cap!
                              Dual sport riders do it in the dirt