Coolant expansion tank cap leaking?

Almost all the people I see use 5/16" I.D. fuel hose and use DexCool 50/50 extended life coolant. In the US the cap on the DexCool container is orange.

5/16 in. = 0.3125 =  7.9375mm

 ".........using a common auto parts store national brand name .................."

I would suggest that you double check its compatibility with the Rotax (mixed metals) cooling system.

Roger Lee's recommendation/experience for the USA market is excellent.

As for "..........antifreeze 50/50 premix" - I don't trust premix's,  much prefer to measure out the concentrate and the same volume of good quality pure water (eg distilled / demineralised / revers osmosis) - depending on system, we are only talking about 3L capacity, not a big cost/effort.

Roger Lee wrote:

Almost all the people I see use 5/16" I.D. fuel hose and use DexCool 50/50 extended life coolant. In the US the cap on the DexCool container is orange.

5/16 in. = 0.3125 =  7.9375mm

 "....fuel hose..."   - Yeah! I at a pinch.

I prefer to use a hose actually rated by the manufacturer (go Gates?) as heater hose, therefor compatible with coolant. We are only talking small diameter, short length, low cost here.

Its great the way you smile (photo) through all the comments from picky illegitimates, like me.

Sean, please direct me to the "mixed metals" Rotax engine coolant “compactivity" table in the Rotax technical data, I can't seem to find any such data.  I have found the Rotax guidance to use conventional coolant including 50/50 premix for Suffix 01 engines such as mine in CH. 75-00-00 of the IM.

Roger, I considered using fuel hose but could not find any with manufacturer's specifications that demonstrated compatibility with coolant and temperatures of 257 degrees F or higher, or, as the IM states, suction "strong enough" (whatever that means) so I passed.  If you know of any I'd much appreciate a link to the data as I do need to replace my overflow line next year- if not sooner. I'd really like to find a source for clear tubing that meets the temp requirements. 

Don't recall ever actually seeing a Rotax coolant specification, however almost all coolants rated for modern European cars with aluminium radiators should be okay.

Go for a  long-life coolant based on monoethylene glycol with advanced organic acid inhibitor technology free from amines, nitrites, phosphates, silicates or other inorganic inhibitors.  Mix at manufactures maximum ratio (usually 50:50)  with pure water - see Roger Lee's earlier recommendation.

Overflow/return hose does not need to be clear/transparent - any good quality coolant hose of the correct ID will be satisfactory (I use Gates products but there are many others).