hey all i have one for you. i have an 81 mercruiser 120 with a prealpha outdrive. last year i was having an overheating issue. on a hot day my engine will overheat but never really get to full hot. it gets to about 3/4 hot maybe a hair over that. i changed the impeller after this happened and it made no difference however when i run it on muffs at home, it can run for hours without even getting to the middle of the guage. i figured maybe it was because of the 110 degree wether being that i live in phoenix and the water temp is usually pretty high. i also noticed on a lot of other posts about overheating people mention a heat exchanger. does every sterndrive have one and if so how is it tested?
