Didn't hear previously about heat exchanger, doesn't change that 
shouldn't overheat at slow speeds. Concur what's said below, and yes 
it's usually exhaust valves that swallow, also due to many have hollow 
stems with sodium for cooling the valve head. The engine does have a rev 
limiter that can be set by the shop. Engine shouldn't of over revved to 
float valves, operator should have set for conservative RPM, points to 
either rev limiter not set/functioning properly, defective valve spring 
or something sticking in the valve train, or of course a defective 
valve. All of this points to the renter. Rev limiters are very common 
today, being easy to implement.

We can talk all we want, and it's going to end up with who has the 
biggest lever, but may be too late with credit card, many have a short 
time (2 days) to protest, should check out with credit card, if later 
you end up paying, there may be interest, etc. Might want to protest, 
pay bill, then get credit later, find out proper procedure.

Bob Blick wrote:
>> Vitaliy wrote:
>>     
>>> Carl Denk wrote:
>>>   
>>>       
>>>> Does this unit have a sealed cooling system,
>>>> or circulate sea water?
>>>>     
>>>>         
>>> I believe it circulates the lake water, based on what I was told and also 
>>> because it's relatively common for the "oil hot" light to come on at low 
>>> speeds.
>>>       
>
> Two things come to mind -
>
> The cooling system is sealed, with coolant in the engine, and connected
> to a heat exchanger to the lake water. So you can overheat the engine
> under any condition if there is low or no coolant. But the lake water
> can also boil when the coolant is fine and not boiling because the
> coolant is under pressure and it's propylene glycol(safer for the
> fishies than ethylene glycol) so it naturally has a higher boiling point
> than water.
>
> Also, you have a broken intake valve. Intake valves break when they
> stick open and get hit by the piston. They stick open because they are
> bent. They bend if you over-rev the engine, the valve floats a little
> and gets knocked closed by the piston. Do that a few times and the valve
> starts sticking and the whole thing goes south in a hurry. 
>
> If it was an exhaust valve it could be something else, but it's an
> intake valve, which run cooler but are heavier and float first when
> over-revved.
>
> Just my 2 cents and general experience blowing engines.
>
> Best of luck with it. I would guess you have a losing fight in court,
> your only hope is if your credit card company can rescue you.
>
> Best regards,
>
> Bob
>
>   
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