Changing thermostat 1992 43L

"Last week my battery was dead

"Last week my battery was dead and after charging and re-installing it in the boat i neglected to attach the second ground which worked the trim. i went to beach it at out local spot and realized a little too late about the battery cable issue. once i realized the trim was not going up i shut off the engine, but i think i sucked up some sand into the water intake because the thermostat will not go above 135 deg. other than replacing the thermostat is there any thing else i should do before running hard? Flush? if so how?"

"When cold, you could try star

"When cold, you could try starting it on the hose, and once you have water flow out the back, pull the block drain plugs alternately for 10-20 seconds. This should give any sand in the block and heads a chance to flush out. It will also tell you if there is any significant amount in there.
Only run it for a minute or two, as the manifolds will not be fully cooled, nor will the heads. You could repeat the whole process 2 or 3 times after letting it cool down in between runs.
Sand will also settle in the manifolds, so you should flush them by removing the top pipe plug on the elbows, and flush down through to the bottom manifold drain with a garden hose as vigorously as possible (engine off).
If you find a bunch of sand, you should consider replacing the pump impeller; very easy job and good insurance. You can then remove the main water inlet hose at the T'stat housing, start it up, and flush the pump and inlet line into a bucket for a short while to clean it out.
Rod"