Mercury 225 promax not sure of year.

by Roger
(Maryville Tn. )

I purchased a bass boat with this motor. The previous owner blew up the 260 that was originally on it ,He dropped on a 225 powerehead but left the cooling system configured for the 260 with no thermostats, just restrictor washers , one piece exhaust adapter plate and no poppit valve. The motor will never warm above 100 degrees in cold water. At idle, the water temperature will reach 170 deg. And more. As soon as I accelerate to cruising speed the water temp immediately drops to 100deg and below. I've been told to change to a 2 piece exhaust adapter, and put in thermostats and poppit valve. I've not run it in warm water yet to see what the temps are. Thoughts are greatly appreciated.