I'm talking about 'modern' vehicles here, ones that use a sealed cooling system, have you guys noticed that a particular make/model may require the expansion tank topping up from time to time where other makes/models, the level between the min/max never changes for months or years even. I first experienced this years ago when the wife and I owned a couple of Fiat Cinquecento's, they both needed topping up now and then, not by much by any means but I did wonder where this coolant were going,.....neither cars ever got that hot or overheated and there were no leaks or white smoke etc. I'm currently experiencing similar with a motorbike, again it's only a small amount over say a 3 or 4 month period, the level seems to want to migrate/stay close to the min mark rather than the middle/max. Could this just be down to the height/position of where an expansion bottle is actually placed on a vehicle??