Never had a prob with the Yanmar 50hp diesel till today.

Two coolant systems - raw water (OK) and closed system - lost all
coolant - refilled - lost it all again about an hour later. Found one
small leak - the top vent hole in the vented loop.

Why is coolant dribbling out of the top of the vent loop?

Luckily the win was beam reach all the way home!

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Molesworth