Why does my coolant level keep rising above the maximum line?

I have a new Ford Fiesta Ecoboost turbo 140PS. After a 400 mile journey the coolant level had risen to above maximum. I removed some coolant so that it returned to the maximum level. After another journey the coolant was again above maximum. 0.5 litre coolant has now been removed. The dealer is adamant there is no fault. What is the cause and what has replaced the coolant?
The turbo of this engine is watercooled and there have been reports of the coolant pipe to the turbo fracturing. The rise in the expansion tank will be due to an airlock, so the engine will currently be running on very little coolant. This needs urgent attention.
Answered by Honest John on

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