I have an Indmar 350, and the normal engine temperature runs between 180-200 degrees. It usually takes about 5 minutes or so to warm up to normal operating temperature.
Also depends on water temp. I noticed that in March it took 5 minutes to get to 160 and it stayed there. Last week, it took 2 minutes to get to 160 and never got above 180.
Temperature should sit at your thermostat reading unless running under a heavy load. If you have a head exchanger and closed cooling with glycol you'll have a 180° or higher thermostat. If you use Lake water for cooling the engine directly you will have a 160° thermostat.
The engine runs less effeciently when cold so you get more plug fouling and gas mileage is down. You might be able to get more raw power out of it though for a short sprint because the cylinders could fill with a colder mixture. It's better to find the right one but nothing is going to blow up.
nacho. If you run in cool water with no thermostat the engine (at least EFI engines) will run very rich. Even so much as to pump gas into the oil. It happened to me.
It seems that my thermostat is not working properly. Engine temperature stays low (full left on the indicator). And uses an awful lot of fuel. (is it also possible to lean the engine???)
Parts are very expensive here in Holland. Does anybody know a store in the US where I can order parts?