>Since the owner was driving in a rapidly flooding
>parking lot in water nearly up to the door sills when the car
>stalled, and the engine never ran again (actually, never turned
>over again), I  accepted the bottom breathing, water ingestion
>diagnosis.

This sort of problem also afflicts motor boats. In this case what can happen
is a misfire in the engine makes the crankshaft kick in the reverse
direction, typically when starting the engine. This in turn can suck water
up the exhaust pipe into the engine, which then tends to cause damaged
pistons, valves and crankshaft when another cylinder does actually manage to
fire.

The standard method of avoiding this problem is to have an expansion chamber
somewhere in the exhaust system which has a volume greater than the total
swept volume of the engine. The incoming exhaust pipe needs to be above the
water level in this chamber if the engine did manage to complete a full
revolution in reverse so it does not suck any water back into the cylinders.

Needless to say this chamber should be above the waterline when the boat is
at a mooring so it is not full of water before you even try and start the
motor!

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