Maxum did not use Volvo only Mercruiser, what outdrive is on the boat? Volvo and Mercruiser both use GM blocks so swapping is a none issue but I suspect the outdrive is still a Mercruiser Alpha.
A friend of mine had the same expierence as you and a year latter lost the engine due to this overheating expierence. I donít trust the helm gauge much and use a handheld IR temp sensor to take readings at the first trip. I also replace the impeller every two years. The helm gauge only provides the engine temp and not the exhaust components.
Best of luck.
1997 Silverton 362, 7.4 Crusaders
1997 2400 SCR, 5.7 Vortec / Bravo 2