OK, I went and helped a friend change the oil and winterize his boat today. He has twin 525sc's and was told by the previous owner that he didn't run thermostats. The current owner says the water temp takes forever to warm up and tops out at about the 130-140* mark on both engines. We both seem to think these engines should have a 165-185* thermostats but not sure. What are your opinions on this? I'm gonna check with a few techs at work tomorrow but figured I will get opinions from here also. Thank you in advance!
Brandon

They are supposed to have 140* T-Stats. Same as all the Merc BBC carbed engines. Mine always ran about 145* on the gauge.

I can't remember, does the boat have cross overs or circ pumps??????

Thank you, and it has cross overs.

I wouldn't worry about water temp too much as long as the water pressures are in the 15-30psi area at WOT. Crossovers often run very cool water temps. Its the oil temps that are more important.