Coolant draining from overflow tube

OK - to be clear, I’m dealing with a motorcycle, but is has a car-like engine (block, 2.3 liter/140 cubic inches). The motorcycle is a Triumph Rocket III. The issue is that after I ride for a distance and park the bike, coolant leaks out the overflow tube when it’s cooling down. Anyone have an idea of why this would happen?

If it was a car I would say a weak radiator cap. Don’t know if you have a cap on radiator. I am also assuming the reason you don’t see coolant when the engine is hot is that it just evaporates.
Had the same problem on my Minivan last week. Loosing coolant but everything looked fine with no leaks noted. The only hint was a bit of crud around the radiator cap. Changed that and all is fine. A $6 repair in my case.

Actually that is when the engine is the hottest. Radiator cap would be my guess too.

Make it 3 votes for a bad radiator cap.

Ditto on the bad radiator cap. The pressure increases when you shut off the engine and the hot spots heat it up with no circulation, increasing pressure. In the days before cars had coolant recovery tanks, the coolant would just go on the ground.

Does it have a coolant recovery tank? If not, you may be overfilling the radiator. Cooling systems without an overflow tank need a little headroom in the top of the radiator.

Is the overflow tube coming out of the radiator or out of a coolant recovery tank which you may be over-filling…??

I’ve owned 3 or 4 Triumphs over the years but my knowledge of water cooled ones is around zero.
Other than a weak pressure cap as mentioned, maybe the radiator cooling fan is not cycling on or running on after the engine has been shut off. If so, maybe the heat spike is causing coolant to puke out past the cap.