When the coolant gets hot it will 'expand' and any excess will go into the expansion tank, hence the name. 
The reason there is an upper level is because they've guessed how much will expand into this tank on a normal occasion so they've allowed so much space in there for this to happen, but if it's already too full it will simply get chucked onto the floor out of the overflow pipe once the levels rise.
*** When the bike cools down the fluid will get sucked back into the main system. ***
If all is well with your system , as in no air leaks or blockages of the waterways or radiator, then the coolant level should stay pretty much the same level in the expansion tank (when the engine is cool, and levels are settled), with maybe a minor top up every 6 months or so.
I haven't topped mine up for many months now!
Just by keeping an eye on that tank can give you a good indication if all is well with the system though so it's a useful visual tool as well.
If your expansion tank is empty then that means you should immediately check to see if the fluid is okay at the cap end under the front of the fuel tank.
If it's okay under the cap then top up the expansion tank to no more than the upper level.
If the level is low or you can't see any fluid then you need to figure out why?
If for instance you had a leak from a pipe up front then you would lose fluid from up front, but when the bike cools down it will suck whatever coolant it needs from the expansion tank, so you would see the levels were wrong, or decreasing, meaning there is a problem.
If you suspect it's a leak but aren't quite sure where from i've always found it easier to take the bike for a quick blast at night, then use a torch on the engine, it will show up coolant stains or leaking liquid much easier than in daytime, but a dark garage will do the same job too if you have one.
The other one to look out for is what i keep harping on about, when you have a blocked system the waterways will be thinner than normal so the coolant won't flow properly and the engine will get so hot that it will push the fluid into the expansion tank until it literally boils, fills the tank and chucks it on the floor. Remember, it's not just antifreeze, coolant has a higher boiling point than just water so if you see or hear it bubbling away in the expansion tank, or fluid is hitting the floor, then you have a problem.
This is the dodgy one 'cos it will just keep chucking it out until you have dangerously low levels of coolant, then that alone can obviously cause all sorts of grief.
That's why i'm such a big fan (excuse the pun) of keeping the system in good condition, it can only be a good thing and when it's all functioning well it is also very low maintenance.
mokin
The reason there is an upper level is because they've guessed how much will expand into this tank on a normal occasion so they've allowed so much space in there for this to happen, but if it's already too full it will simply get chucked onto the floor out of the overflow pipe once the levels rise.
*** When the bike cools down the fluid will get sucked back into the main system. ***
If all is well with your system , as in no air leaks or blockages of the waterways or radiator, then the coolant level should stay pretty much the same level in the expansion tank (when the engine is cool, and levels are settled), with maybe a minor top up every 6 months or so.
I haven't topped mine up for many months now!
Just by keeping an eye on that tank can give you a good indication if all is well with the system though so it's a useful visual tool as well.
If your expansion tank is empty then that means you should immediately check to see if the fluid is okay at the cap end under the front of the fuel tank.
If it's okay under the cap then top up the expansion tank to no more than the upper level.
If the level is low or you can't see any fluid then you need to figure out why?
If for instance you had a leak from a pipe up front then you would lose fluid from up front, but when the bike cools down it will suck whatever coolant it needs from the expansion tank, so you would see the levels were wrong, or decreasing, meaning there is a problem.
If you suspect it's a leak but aren't quite sure where from i've always found it easier to take the bike for a quick blast at night, then use a torch on the engine, it will show up coolant stains or leaking liquid much easier than in daytime, but a dark garage will do the same job too if you have one.
The other one to look out for is what i keep harping on about, when you have a blocked system the waterways will be thinner than normal so the coolant won't flow properly and the engine will get so hot that it will push the fluid into the expansion tank until it literally boils, fills the tank and chucks it on the floor. Remember, it's not just antifreeze, coolant has a higher boiling point than just water so if you see or hear it bubbling away in the expansion tank, or fluid is hitting the floor, then you have a problem.
This is the dodgy one 'cos it will just keep chucking it out until you have dangerously low levels of coolant, then that alone can obviously cause all sorts of grief.
That's why i'm such a big fan (excuse the pun) of keeping the system in good condition, it can only be a good thing and when it's all functioning well it is also very low maintenance.
mokin
More people are born because of alcohol than will ever die from it.
