if you are lucky, you just fried the innards of your exhaust
hose and impeller. you are lucky your mechanic
caught the collapsed hoses. i have seen situations where the inner wall of the hose partially collapses only at high temperatures. what's happened is that the high heat has delaminated the walls of the hose from each other . the hose seems to be fine at idle but collapses at high rpms . can happen to raw water
inlet hoses if the water
pump supply hose is close to your overhot engine
block. this one is a devil to sort out.so to be safe, i'd also replace the hoses that were closest to your hot engine
block: ie the ones feeding into the front of your heat exchanger and possibly the hoses into /out of your raw water pump. did you say th boat is 30 yrs old? it's likely the hoses are too. to save some mechanic
$$$, you can replace some of those hoses yourself....
it may be time for a valve job .setting the clearances of the inlet/exhaust valves can be done by your mechanic with the boat in its slip. if necessary he could also replace the head gasket
and retorque the head
bolts. knowing mercedes heavy duty construction, it's possible that's all your engine will need. and those are eventual regular maintenance
items any way...
three ideas for you:
(1) put a rope
loop on your engine start key. drape your engine start key on top of your raw water inlet seacock handle when you close the raw water seacock after a sail.. so next time , you cannot start your boat engine without remembering to open your seacock...
(2) there is an aftermarket band- style exhaust alarm
made by borel. it is reasonably priced and sounds a shrill alarm
to wake the dead when your engine temperature gets higher than about 200 degrees. the alarm is very reasoanbly priced about $80 or so as i recall
. it is a self install and the only size you need to know is the circumference of the exhaust hose. i have a temperature gauge and audible temp sending unit on the engine block, but i added the borel as a safety
backup. costs less than 1 hour of mechanic time....
(3) don't be upset about forgetting to open the raw water inlet. most everyone does that sometime. just make it a beginning lesson in your upcoming wonderful years of boat ownership
and NEVER crank your engine repeatedly (ie more than 30 seconds cumulative) with the r w seacock open, as your faithful r w pump will eventually fill up your exhaust with water, which could back in thru your valves and do horrible things to your piston crowns...