The answer to that question is not nearly as simple as non-owners tend to assume, and would depend on details of your definitions. Critic's reply is about as good as any equally brief answer. Should we assume "electric power" in the question means energy coming from the battery, considering part of the power from the engine is handled through an electrical route, even at times when net current to the battery is zero? How are you going to count miles the car is rolling downhill or coasting with no power supplied by engine or battery? Bottom line, ALL the energy to make the wheels go 'round comes from the engine, directly or indirectly. At ~107k, my same-age Prius has had very few problems so far, all minor body issues. I'd consider head gasket failure at only 185k in a well-maintained, non-abused vehicle evidence of inexcusably poor engineering.
Originally Posted by The Critic
Originally Posted by spasm3
How many of those miles were with the engine running vs electric power?
... The gas engine is always running at speeds over 42 mph and during moderate to heavy acceleration at any speed.
Originally Posted by Marco620