I got my first bike in 28years this past June,an 05 CRF450.I don't get to ride much so the bike has appx. 8hrs on it,and up until this point it has been great.I have done normal prep before and after each ride with no problems at all,however I fired it up today to let it run a bit(I live in very cold weather) and after maybe 8 or 10 min. it started to spit antifreeze out the overflow tube and started to get very hot.The only thing I could think of that was different was that I had changed the oil and filter,although the flow looked good I let it cool down and replaced the filter just to be safe.I refired it and after maybe 10 min. it was spitting some out of the overflow tube and showing some signs of steam as well so I shut it down.As I said this is my first bike in 28yrs so my knowledge of the 4 strokes is very limited,I thought maybe the rad. cap might have gone bad.I figure when in doubt ask,so if anyone could give some input on this it would be great.Please help an old dirt eater with some new knowledge this will probably be the last bike I get so I really want to take good care of it and avoid costly repairs.Many Thanks ahead of time.ALB