[subxero]

Sounds like your bike was overheating due to an issue with the cooling system.

Do you know does the bike have a safety feature where it shuts down if it gets too hot?

Just my thoughts

So your cooling system wasn't working 100% which made it unable to keep the bike at a stable temp. Low on coolant is definitely a possible issue. In my experience coolant doesn't just disappear with out an underlying issue. It either gets boiled off but is typically very obvious when it is spewing out the over flow, you can also lose it if you drop the bike and it flows out the overflow, other than that, water pump seal is bad and you r losing it out the weep hole (if it has one) if no weep hole you will see it in your tranny oil or whatever is on the other side of the water pump shaft seals. other possibility is head gasket leak, coolant could go either way and lastly a hose leak.

When coolant looks black in my experience it can be head gasket leak, deteriorating hoses, oil seal and water seal on the pump shaft, and finally if the pump propeller is black and it comes loose it can rub on the cover/case whatever and it can turn the coolant black.

The change in idle could be an air leak caused by a bad head gasket, it gets bad enough when it gets overheated and that is when you notice it.

I would monitor the coolant like a hawk, check level before every ride, if you notice it getting low you know you have an issue.

Keep an eye for any coolant leaking, if it is on the head it will most likely evaporate off when the bike is quite warm but sometimes it leaves a residue stain. Keep an eye on the overflow tube and the weep hole (if there is one) If you notice the coolant getting low and see nothing wrong with what is mentioned, drop the oil into a clear container and look for coolant and or milky color.

Good luck