hey guys, new to the forum...I been working on this bike for a while now. replaced the cam as the exhaust lobe was worn all new valves etc done by qualified persons. put it back together runs great. however it started overheating. now If I run the bike without the rad cap on it won't overheat it will still there and idle all day long no problem. I have purged the system, tried a different rad cap, put a new impeller on, as soon as I cap the system I can't ride no more then one min and the light comes on. I'm going to flush the rad tommorow but I don't think that is the issue. dosen't make sense that the bike won't overheat when the system is open but as soon as I seal it the antifreeze must boil right away :/ any suggestion to help me as I'm running out of beer trying to figure this out. thank-you.

 

Welcome to the forum! If you didn't open the 10 mm bleed bolt at the back of the head by the sensor to purge any trapped air this could be the reason. Leaving the cap off helps,but you need to bleed the system at the engine before any damage happens. Heads,cylinders can warp and you can seize a piston if you let it go too long. OPT

 

found what I think was the bleed. it was a torx head just above the exhaust manifold. however after opening it and filling the rad no changes so with only understanding that it won't overheat without the cap on it's going to have to take a trip to the shop I've exhausted what knowledge I have.

 

NO,it's a 10 mm bolt toward the rear of the head close to the temp sensor that's mounted sideways in the head. You can open this enough to allow coolant to flow out along with any trapped air bubbles. When nothing but coolant comes out tighten the bolt. OPT

 

as mentioned, it's most likely an air bubble that is turning your light on. it doen't take much air to do either.