If you have comprehensive coverage it will be covered. 'Flood' is a named peril listed in all auto policy contracts and most likely will be covered without a deductible.
No. Insurance does not cover mechanical problems.
Only if it was caused by a collision or sabotage.
Auto insurance covers damage caused during an accident. If the engine is damaged during an accident that's covered. If it's damaged for any other reason then that isn't covered.
Possible internal engine damage.
No. But if you have proof positive that the mechanic caused the damage, HIS insurance will cover the repairs. Call your local office of the State Attorney General.
perhaps failing oil pump caused engine damage
The cost to fix a flooded engine can vary widely depending on the extent of the damage and the vehicle's make and model. Minor issues may only require a few hundred dollars for repairs, such as replacing spark plugs or draining the fuel system. However, if the flooding has caused significant damage, costs can escalate to several thousand dollars if major components need to be replaced. It's best to get a detailed estimate from a qualified mechanic for an accurate assessment.
engine implodes
Engine, not motor, and that depends on your insurance policy. If you don't have flood insurance specifically, flood damage is typically not covered.
Oh yes!
Blown head gaskets.
the engine is flooded with gas