replaced a new impeller on my 2008 H190 Mercruiser 4.3 Gl-J SX-A (first time its has been replaced). The first time it was on the lake sounded like no water was flowing through the system and sounded like it was running hard (this lasted only a few minutes and only this one time), then saw that the fresh water flush cap was off, after i screwed it back on, water started pumping through the engine and normal operating temp lasted all day, does this need to be an entirely closed system for the water to pump through?
Since then every first run of the day it overheats until running speeds where normal operating temps maintains the rest of the day (even after sitting after 2-4 hours). Does the impeller swell that much where the shaft wont turn when it sits for a few days? Does this sound like a water pump issue? All other fitting are tight and no water is in the bilge after all day.
So not sure why the engine overheats when we take it out every 3rd day on the first start, then at running speeds it cools and lasts all day at normal temps and engine sounds great. We run in very clean lake water. Any help would be appreciated
(First start of the day the engine warms up and starts to overheat, once the gauge starts to overheat i get the boat up to running speed almost 1/2 to 3/4 throttle and then cools down and for the rest of the day it runs an operates perfectly even after sitting for up to 3-4 hours before starting again).