Stop Start in new cars

[sonarbell]

Just some thoughts on the above..

1. Engines only run at there maximum effiency when hot. So how can they ever reach optimum temperature when stop/starting in traffic all the time ?
2. Catalytic converters only work when hot. So how can they ever reach optimum temperature when stop/starting in traffic all the time ?
3. Engine wear increases with repeated thermal cycling. What will this do to engine reliability on cars as they age ?

Anyone any thoughts ?

[feelluckypunk]

Efficiency is the key point .
You can use stop start to shut down some of the cylinders. Engines don't necessarily work better when hot, you make be thinking of oil temps when warmer are less viscous, better mechanical efficiency, oil cools slowly. But with no combustion thermal efficiency increases instantly as less heat lost through cylinder walls. Reactivating cylinders at first will cause high carbon monoxide levels, I think this is largely eliminated with BMWs valvetronic system as the valves throttle with variable lift, air fills quicker as inlet at ambient pressure. compared to conventional butterfly throttles when under part load there is a vacuum which the engine works against so higher CO levels.

[sebhaque]

The stop-start system in a 1 series I recently drove wouldn't kick in until the engine had reached its operating temperature.

As far as I'm aware the starter motors are also beefed up, although I read this in TG magazine and could be wrong.

[EDLT]

It only starts stop-starting once the engine is up to temperature. Even then you have to have the handbrake on, be in neutral and have your foot off the clutch. As soon as you press the clutch (on BMWs, anyway) the engine starts.

[kambites]

Yup, I think they've thought these things through, somehow.