99 searay sundancer cruiser, dual 4.3 efi, alpha outdrives..190 hrs total, stored mostly but ran once or twice a year....i bought it and went through it completely, from outdrive pumps to everything on engine, plugs, wires, fuel systems, filters etc...was having a bit of vapor lock down at Lake Powell, pretty normal for down there, no matter the boat...put 140 thermostats in it and vapor lock went away, i was also being more careful about overall heat management with daytime temps going over 100 F....i've put about 20 hrs on engine since thermostat change-out with no problems...getting ready for tomorrows trip back to L. Powell and ran engines on hose...left engine would come up to temp about normal, but would then would fall off back to 100 F and then come up or down seemingly independent of throttle setting (up to 2500 rpm with good water pressure on hose)..no water leaks in boat or outdrive, engine temps were cool everywhere to the touch, including thermostat housing and all hoses...after shutdown and heatsoak stabilized, engine was only slightly warm...no startup problems, or any run problems up to the 2500 rpm previously mentioned....i'm thinking temp sensor sender, maybe ?...the water temp warning horn doesn't actuate
