Is the hit-or-miss mechanic doing better than you can do? Is he charging
hourly to run your boat for this effort?
The reported effort / results are at the DIY
level, unless I'm missing some "magic".
The mechanic "progress" would make me INSANE (more insane than usual).
The boat needs to be operated under the problem conditions, then those conditions changed to discover when the problem fails. Doing things like changing throttle position is just one example.
Opening the hatch once the problem occurs, to cool the engine so the problem clears, is not very useful. Soaking the engine in the problem condition, so it doesn't clear once the hatch opens would permit using freeze spray on a component to better understand the problem. The systems that could be targeted are: the ECM; the distributor base and the exhaust temperature sensor.
Has it been confirmed that the operational exhaust may be continuously hand-held? Has the raw water
impeller been confirmed to be good? Have the raw water
passages been back flushed? Has the raw water intake screen
/ strainer been cleaned?
Did the mechanic operate w/ the DDT connected, or connect afterwards to determine if fault codes existed? If so, what faults were detected. Note the DDT tool has been discontinued
although used examples pop up on eBay.
The correct FSM is invaluable when analyzing the problem. As was stated, there are diagnostic tables to pinpoint the possible causes.
All this beats the heck out of the current
Your boat should be capable of proper operation w/o extra cooling added. IMO adding the proposed extra cooling modification is just another shotgun repair attempt. I would guess the implementation by this "mechanic" would result in totally unacceptable audible noise
in the cockpit
. First locate the problem, then determine the solution.
Note, my southern Florida
boat now has a custom thermostatically-controlled heat exhaust system that I designed, fabricated and installed to resolve a vapor lock problem that occurred after stopping for an hour, then being unable to restart until the fuel rail cooled. Now my heat exhaust blowers kick on and off, maintaining my engine room temperature, I now never get vapor lock and can always restart my engines. My implementation adds ZERO extra audible noise in the cockpit
. This heat soak vapor lock was never a problem when operating in New England