250-500cc 0/10 300 boiling

A mate had his 300 boil a couple of weeks back,its heading into Summer down in OZ.I sugested looking at fitting a Y into the Rad hoses like the 4 strokes,anyone done this.

Mine boiled once after I had been stuck for a while with the motor running and not moving. I rode it a lot in Queensland during the summer on tight and slow technical hills etc without a problem. They don't seem to have any real overheating issues and once you are moving even slowly they stay cool.

My 10 mod blows some steam ever now n then I though I had a hole but on inspection all is good so I forgot about it se wot happens next ride

Well, what made it boil? Was he stuck on a hill and working the clutch? Pinning it to get it unstuck from something? Anything will boil over if you make it...
I am curious because my bike boiled over once. It was a super steep hill that I started in 2nd gear by accident. I abused the hell out of the clutch because if the split second of a downshift would have lost all momentum and I would have been stuck and had to go all the way back down and run it again. It was H.O.T hot when I was done. Boiling and hissing and spewing steam. Not happy with me at all. BUT, no fault of the bike...I abused it and it let me know.
I will say this....that bike -09 300- got up that damn hill in second gear ALL STOCK except tires (tr 038 in American Fork Canyon, UT) It was amazing!! Even the KTM 525 I was with had to run it a couple times to make it up.
Also...They will also spit out coolant if you overfill the radiators.

Mine boiled once when it was still pretty new and had the original coolant in it. It was early spring and we were dealing with a lot of fallen trees and miles of slow speed crawling, so its to be expected. Other than that (and the story below) I've had no issues with overheating.

Just this summer I spent a month riding it at high elevation with a hole in the rad. I had no idea there was a hole and chalked it up as heat, elevation, no humidity and riding in sand making it hiss and steam from the cap. I probably put a few hundred miles on it and ran it bone dry more than once without ever knowing there was a leak. It wasn't until I got home, filled the rad and saw a puddle on my garage floor did I find out about the hole.

I've also drowned it in a river by sucking water through the intake.... just flipped her over, drained the cylinder, wrung out the air filter and put in a new plug to get back to camp. This is one tough motor.
I take care of my stuff

He is on a ride at Bulladela this weekend,I hear he has changed the coolent from one that doesnt corrode to one that supresses boiling so will see what effect that has.

hay zim i ride the other side of the highway at bulla in the walangat/bacholor natinal park exllent spot.
hay pc i sunk my 300 twice in 2 days the hole in bottom of the air box is way to big for a drain bit of duck tape fixes it with a small hole to let any water out

We run evans npg in all our bikes, we never have a problem with boiing over no matter how hot or tight it gets.

Check the jetting, mine would boil in tight slow hilly stuff, I put a richer pilot in and it rarely boiled, i have a JD jet kit in it now and runs better also.

put new coolant in the big rig rode the weekend still bubled over 3or4 times havent chek it but i could smell it wash it 2moza and chek level

I have an 09 300 that I had problems with it boiling over a few rides. I changed coolant, and put some 2cool in the engine oil. Still had the problem. Found that one of the radiator hoses had a tiny hole in it that only leaked when engine was running and it had pressure on it. Changed the hose and ridden and raced since with no problems.