Swede

Have have a pair of 502's putting out about 550hp(30' Spectre). We just put them back in the boat with 160 T-stats. The water pressure was 25+ at 2500rpm so I have ordered the Mercury water relief valves discussed in previous post to hopefully solve this problem.

My other problem. I was getting to 200 degrees on the temperature gauges without the T-stats opening. On occasion when I pulled back to idle they appeared to open sometimes as the temp would drop to 165. We drilled one 1/8" hole in each T-stat. Was the excess water pressure causing this or something else? Both motors were doing the same thing.

racinbird

If you have a crossover style cooling system then you do need holes in the T-stat. As with the high pressure I'm not too sure what it can do, I have some pressure issues to work out myself this spring.