yeah I too have the 15hp version, looks the same, but lighter. Same tell tale behaviour. Many take the stat out and run a fast telltale but then it doesnt reach the right temp when operating
Completely normal on these mercury-built mariners. I have a 15hp and it’s exactly the same. Just watch for water getting into the cylinders through the exhaust baffle gasket- the gasket burns through over time. Enjoy the motor 👍
