Coolant leak at side of the road

[Dr. Zed]

Here's a tip I heard from more than one BMW mechanic - never fill your coolant tank to full!
Just keep it at the lowest indicated level possible, especially in summer.
You'll thank me later.

Well I assume without anything resembling an overflow tank, any coolant passed max is just going to result in over expansion of the tank. But the level was definitely not more than the max at cold, that's for sure

[Chris_D]

Here's a tip I heard from more than one BMW mechanic - never fill your coolant tank to full!
Just keep it at the lowest indicated level possible, especially in summer.
You'll thank me later.

Well I assume without anything resembling an overflow tank, any coolant passed max is just going to result in over expansion of the tank. But the level was definitely not more than the max at cold, that's for sure

No I think the point is that the expansion tank is too small to compensate for expansion when running hot if the reservoir is kept topped up to max. Hence if you keep it at the lowest indicated level there is more room in the system for expansion.
There is a relief valve / vent for over-expansion but it’s obviously not effective enough to prevent the expansion tank from splitting when hot.