Topped up my engine coolant to the max marker just before an 80 mile round trip, checked it when I'd got home and noticed it had gone down by about a quarter of the distance between the min and max markers. Should I get this looked into? Surely it shouldn't lose that much that quickly

from what I understand about cooling systems with expansion tanks, this system is really different from the reservoir tank systems, our system , the expansion tank system , is a pressurized system, and the tank cap acts as a pressure valve that is designed to keep the pressure constant , about 21 psi according to factory specs, when the engine is cold , the level should be somewhere between the max and min mark , when you top up to max when cold, then you drive, the coolant expands as temperature increases, this expansion will create more pressure, which will be released by the coolant cap valve as vapour, until it is 21 psi again, that's said, when cold the level should be between the two marks, actually close to minimum, when hot, the level will rise to max or may be above max by a little bit , until cold again it will return to the previous level, so if you continued to top up to max when cold, the level will drop again to a level where equilibrium happens, and stick to that level. 

so my advice, don't top up again and watch for the level regularly , if it dropped under the min mark when cold then there is a problem that needs to be checked, if it sticked to a level between the max and min marks , then its ok and no need to worry.

@Eng_Ahmad1986 Thanks for the information, i'll keep an eye on it

If it keeps happening I would get the car in to be inspected, it could be a blown head gasket and the engine could be either leaking or burning coolant. 

47 minutes ago, runamonk said:

If it keeps happening I would get the car in to be inspected, it could be a blown head gasket and the engine could be either leaking or burning coolant. 

Very much doubt it.   If the head gasket was blown the level wouldn't be between the min and max markers it would be well below the min marker.

 

Depends on how much is leaking, if it's leaking internally and burning coolant that could lead to overheating and eventually cracking the block. It's a well known issue. I wouldn't be so quick to dismiss. I would get this checked while under warranty.

Mine had a slow leak through cracks in the expansion tank that only leaked when very hot. New tank and cap fixed it.