Stop Start Technology

[PlaySchool]

Does it save petrol? It sounds like a lot of energy is used to restart the engine. Would it be better to keep the engine ticking over at the lights? I'm confused!

It depends how the system works, I should think. If done properly, the engine is stopped with one piston just before top dead centre on the compression stroke (so there is an air/fuel charge in the cylinder). When the starter is engaged, that cylinder fires almost instantly meaning less load on the starter compared to when normally starting the engine.

Given that cars with stop start tech are the eco-conscious sort, they are likely to have some sort of regenerative braking system that will power the starter (which is often a combined starter and alternator).

Overall, it should use less fuel; how much depends on how often in a journey you spend at standstill.

Thanks, mittens. I'm just wondering if I should disengage it or not but your explanation makes more sense to me now.

Can't comment from a professional level, but can say that since we switched to a car with Stop-Start, our petrol bill has plummeted!

Really? Do you have a smaller engine than before?

slightly smaller,not something that will account for SUCH a difference. we used to fill a tank of petrol every week, now we drive roughly 1.5 times MORE than with the older car and we fill a tank once every three weeks. It's really good if you have a trip which includes stop-starts (ie- lots of slow traffic/traffic jamms)

I have a hybrid with stop-start technology and we fill up the car once a month rather than 3 times a month.

Thanks MooMe and Babydude I will switch my stop start back on. I have a Fiat 500 which I got after having a Ford Focus. I'm seriously hoping my fuel bills will be less.

MooMe and babydude

How big were the fuel tanks in your old cars, and how big are the fuel tanks in your new cars?

The size of engine is not (on its own) an indicator of fuel economy, there are too many factors that affect it. In general, newer engines are more fuel efficient (so therefore for a given driving style, give better fuel economy) than older engines.

So, a smaller, newer engine should show better economy than an older, larger engine. E.g. the Fiesta ECOnetic claims 85mpg (1.6 diesel) and Polo Bluemotion claims 80.7mpg (1.3 diesel), up from 67ish and 75ish from the earlier models respectively. A 1.5 diesel Qashqai gets 47ish (from the trip computer). My Honda's trip computer suggests just over 50mpg from its 2.2 diesel, with my driving style.

My BMW with stop/start gobbles fuel at an eye watering rate. Love it though!

My old car was a Honda Accord 2.1l fuel guzzler.

My new one I have no idea of the engine size, but its the old style Honda IMS with stop start.