The first thing I would do is get the radiator cap pressure tested. The radiator cap act's like a one way valve and will lift when the pressure gets too high but they can fail and cause the steam you see. Do you know if your radiator fan is working?

 

It's a simple idea really. The liquid expands and pressure builds as the engine heats and some of that gets pushed out into the overflow. That inlet into the overflow is at the bottom of the reservoir, so it's under the liquid level.
As the engine and the coolant inside it begins to cool off after a ride, it contracts. Being a closed system, it's not allowed to vent that vacuum it creates so the vacuum is felt at the inlet at the bottom of the reservoir, therefore it sucks all that coolant back into the system as things cool and contract.
It's really possible for you to get some steam out of the reservoir after a ride on a cool day since when the engine is first turned off, the fluid is probably pretty hot still.
When we top off a cooling system in a cold engine and close it up, some of that fluid gets pushed out but not 100% will make it back into the system. The system will reach a point of equilibrium to the point that it does have a little bit of space at the top of the radiator, an air bubble.
In a properly working system I generally always notice a little air pocket under the radiator cap when I check it, but I always top it off. Usually not much, only a quarter cup or so.

 

When you refilled with coolant did you fill at the radiator cap and purge out the air?

 

Cheers for that Beezer - I now understand! Nicely explained.

And cheers JPR and smilie - definitely on my list to check out

 

Where is the steam coming out of your expansion tank, your radiator, your engine?

 

I think if it were totally pressurised it'd be a bomb eventually.

 

My instructions include "burping the system" does your manual require such???

Unfamiliar with your 1100 though, most require this "burp"

 

I do not see any one way valves on the system.

Then put your radiator cap back on. As jpr1968 pointed out the radiator cap IS the one-way valve.

As I understand it, the coolant system is under pressure - but how can this be if the coolant reserve has an overflow tube?

Are you talking about the reserve bottle located under the bike just in front of the rear tire (as Beezer surmised) or the overflow hose that runs down from the radiator cap opening?

The former would be a matter of serious concern. The latter not so much -- probably a loose radiator cap.

Other questions:
o When you refilled the radiator, did you use new coolant?
o If so, what did you use? If not, why not?
o What instructions did you follow when you refilled?
o Did you put in as much (or more) than you drained?

 

I m guessing you mixed the coolant with too much water and it boiled

 

Caps actually have two valves on them a pressure relief and a vacuum relief. The big spring with the flat rubber face at the bottom of the cap is the pressure relief. When pressure gets above spring pressure it pushes up the spring and coolant flows to your overflow tank. These generally are not prone to failing that often. If you look at the bottom of the cap there will be a small circle in the middle. Take your fingernail and pull it out. It is the vacuum breaker. Its also under spring pressure and when your cooling system cools down, the pressure falls which can cause a vacuum. When the vacuum gets to a certain point it releases to suck the fluid from your overflow back into to rad. This also keeps your radiator from being crushed like an aluminium can. These fail more often than the pressure relief part of the cap. Sometimes the spring will be broken and you will see it hanging there. When this happens, the radiator can not build up pressure and at atmospheric pressure the water will boil at 212* F. The more pressure you have the higher the boling point of the fluid will be. At around 29 inches of vacuum, water will boil at room temperature believe it or not.

So I would either get your cap pressure tested or just get a new one for it.

 

For every pound of pressure the boiling point of water increases 3 degrees. So if you have a 10 pound cap the water would not boil until 242 degrees.