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Believe it or not i changed the radiator cap about a month ago, might aswell do that again too? I have a feeling my thermostat is contributing the most, as my top radiator hose gets alot hotter than my lower one. Coolant is brand new, ever since it's been leaking out i've just topped up with water (I was always in town when it happened) but when i take the cap off it's still bright green so there's plenty of fluid in there. The bubbling did only start when i changed the radiator cap actually.. Within 1-2 days, could have never thought it could be a problem?
What radiator cap are you using? I had trouble getting the Trident brand radiator caps to seal properly on my VS, I than went back to the CPC brand radiator caps which work much better.