Keep a check on the fluid level, because it is normal for the coolant to be agitated in that bottle while the engine being ran, but if you see it fill or over flow it could just be the level of coolant in the radiaton leveling out & over flowing what is expanding.
The key when watching that over flow bottle, is when it fills or even over flows when the engine is hot, then once the engine is completely cold & you start it back up, IF that coolant in the bottle not being sucked back into the radiator, that is a good indication the cooling system not a closed system & theres a leak somewhere.
This is why it is so important, to do the cooling system pressure test Carlos has mentioned several times, to see if the system is closed to be sure of no leaks.
One way I have found over the years, to tell if a head gasket is leaking. When you first start the engine up cold, remove the radiator cap & look at the flow of coolant down in the radiator, if it is calmly flowing not all agitated, you can pretty much figure the gasket is sealed, but if its all agitated like when you look at it, it is because compression is being blown past the gasket into the cooling jacket & causing the fluid to be agitated.
That coolant catch tank, all of you that still have one, it is a tattle tail of sorts, to let us know when something is wrong with the cooling system to alert us to check the engine over.
Neil
