I ride extensively in the Philippines where it is damn hot, probably hotter than Cambodia.
My WR450 will boil sometimes on long slow technical sections and once it cools the radiator is always
full. If not to the very top, very close. Never do I open the cap and NOT see coolant. The critical
thing is the catch bottle must have coolant in it, and the hoses between the tank and radiator must
be in good condition with no leaks or kinks.
If all that is as it should be and you still boiled enough coolant out of the radiator to not see any
you must have got it really really hot... If the system is tight and working as it is supposed to
it SHOULD eventually draw the coolant back into the radiator after a few normal heat/cool cycles.
Of course, you can also just top it up manually and avoid the wait as you did.
I've been to the Phils and it's about the same as Cambodia: hot and humid as hell.
To be honest, I usually never had this problem with my old radiator cap. If I noticed I had boiled over, I'd wait a bit and the coolant would get sucked back in. However, that old WR radiator cap's seal conked out a few months ago. With no OEM in sight, I replaced it with a Yamaha R1 cap... 1.1 Bar and fit is the same. Seemed to work alright. Maybe a week or two after I started using the R1 cap, theTusk 1.6 I had ordered arrived, so I switched to that. I don't recall ever boiling over with the 1.6 on. When I removed the 1.6 cap a few hours after a ride, the radiators would always be full.
Then two weeks ago my waterpump seals gave out. I was worried the 1.6 Tusk might have caused the seal leak (more internal pressure?), so I switched back to the R1 cap before last week's ride. Maybe the used R1 cap is also toast, so it didn't suck it back in? Should I put the 1.6 back on and see how it goes? It seems like tons of people run the Tusk 1.6 with no problems at all, so perhaps the seals weren't installed properly and the 1.6 has nothing to do with the blown waterpump seals.
Good post DPB it also gets hot in baja. In our Wrs we run 100% car coolant no water.They may run slight bit hotter,but don't loose coolant or boil over ever. We have done this on all our bikes since 1987.
That's weird... I've heard about people doing this before. I've also heard about people only running water... A guy I know informed me that since coolant/antifreeze is thicker than water, it doesn't circulate as well, nor does it carry heat away as well as water. So running more water has better cooling properties than simply adding more green coolant... Thus I've been told two things: some people run ONLY antifreeze, while others run a way higher water-to-coolant ratio. I've tended to stay in the 50-50 range. I'm not arguing with your years of experience, but wouldn't a car or bike on 100% coolant actually run way hotter than if it had some water in there?