Re: Input on running temp. 02 Merc 350 Mag St inboard
LT,<br /><br />Yeah, you're close, but just imagine the system when the thermo is fully open. Typically a 140 may be fully open at around 155 and the 160 at 175 (somebody chime in who knows, but I use about 15 degrees between closed and fully open). So if you are getting above 175ish with a fully open 160 thermo, then the 140 won't help. This is not true with the thermo removed as you get bypass, which messes up everything. When a manufacturer does a cooling system audit they typically use a blocked open thermostat. This way they get the flow the right direction and still have the correct orifice size in play too. That is how they judge the efficiency.<br /><br />If you take a 160 that never runs fully open because it just doesn't get that hot, then yes a lower degree thermostat would potentially reduce your maximum temp too. The point is that a lower degree thermo will not help if the engine/system is truly overheating. If you just don't like how hot it is running AND the current thermo is not required to fully open to cool it, then yes, a lower degree thermo would get you lower min and max temps. But if I take everything in your first post as correct (i.e. gauges are right etc.), then a lower degree thermo is the wrong way to go. The way YOUR boat runs sounds right to me, there is plenty of cold water available, so it stays right at the opening temp . . .<br /><br />I am confused why your '06 has a 140 though. I don't know, but thought that all of the open system Mercs were running 160s now . . .
