Hopefully it's something simple/inexpensive. Water temp can be deadly on a outboard. Running to cold can be as bad on one as running to hot. Need to really make sure to let them warm up before running them at higher rpm's. I have as smartcraft gauge on my Merc so it's easy to tell when it reaches the right temp and thermostat kicks in and cools it back down. Takes about 3 minutes or so in the colder water and air temps to get to 140 and then kick in and take it back to the 130's.