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Comment by Jonathan Porter on April 24, 2011 at 11:23am

Stay with the 50/50 - better cooling - honestly.  Try to use Glysantin or BMW motor car coolant (it is the same thing) - it will be greeny coloured...  To purge air, I pump the hoses with the tank cover off, you can see and hear the bubbles coming out.  Once as full as you can get, run the engine for 10 minutes, let it cool and then top up on the tank itself, making sure the overflow is about 50% - it will sort itself out after that!

Comment by Bob McDonald on April 24, 2011 at 8:20am

It is probably not the radiator itself. Usually its a simple tighten of the radiator hose clamps. You can buy (automotive store) a higher quality of gear clamp with a stainless liner sleeve to prevent the clamp from cutting the hose when tightened. These clamps are "spring" tensioned and called a constant tension gear clamp. I would recommend changing the radiator hoses every 5 years as they tend to harden with age.

Comment by Gary Buster on April 24, 2011 at 7:16am

Thanks Bob... I'm doing just that on the bleeding... but I'm still using the rotax recommended 50/50 ethylene glycol...   and of course, now I've found a weeping spot on my radiator... Dang... deconstruct yet again!!

Comment by Bob McDonald on April 24, 2011 at 6:57am

No secrets... its as simple as draining it, re-filling and letting the overflow bottle top up the volume of any trapped air as it bleeds off with the heat of the engine being run then allowed to cool. When you changed out the coolant I assume you installed the recommended EVANS NPT waterless coolant recommended by Rotax? EVANS is a lifetime "waterless coolant" that cost $50 for a gallon, you dont not mix with water, it takes about 2/3 of a gallon for the Rotax 912 coolant system....unless you have the larger belly radiator?