Hybrid engine starts / stops (Score 1)

Starting a regular engine is a scary proposition. A starter motor is mechanically connected to the engine, and forces the engine to turn at maybe 500 rpm. Fuel is injected into the cylinders, and ignited, forcing the pistons down. The engine suddenly finds itself jumping from 500 rpm to 1500 rpm. The starter motor must immediately disengage from the engine. The engine block, initially quite cold, finds itself rapidly heating due to the fire inside it. Parts rapidly expand.

Starting the Prius's Internal Combustion Engine (ICE) is a more gentle operation. A hot water bottle injects the hot coolant into the block, preheating the engine block. The power is applied to the electric motor connected to the "sun" gear of the planetary gear system, which in turn causes the ICE engine connected to the planet gears to start turning. Once the ICE has been gently spun up to 1000 rpm, fuel is injected into the cylinders, and ignited ... but only a little fuel is required, since the engine is being spun by the electric motor. As more fuel is added, the ICE takes over responsibility for turning itself over, and eventually providing the power to turn the electric motor as well ... turning it into an electric generate which recharges the battery. It is complex ballet, but the result is significantly less stress on the engine components.

When the Prius's ICE shuts off, the hot engine coolant is shunted off and stored in the hot water bottle ... to be used to pre-heat the engine block the next time it is started.

True, the Prius's engine is more complex. But much of that complexity goes into prolonging the life of the engine.