Economical driving

[SCCheshire]

Does switching the engine off at traffic lights make for good economical driving? The car is a Corsa diesel.

[Toureman]

Won't realy make any difference at all to your MPG as the petrol you saved will be used charging your battery up to the state it was before you started your engine.

All it will do is annoy impatient drivers behind you waiting for you to start your car.

[SCCheshire]

Thanks Toureman. Your answer serves as amunition against my husband!!!!

[chas2008]

er, sorry ...but there is or was a vehicle for the life of me i cant remember the manufacturer, but it did turn off when stationary and restarted when the throttle was depressed, the object being economy....

[SCCheshire]

Oh no Chas2008 that is not the answer I wanted!! We females should be allowed to win some of these motoring debates!!!!

[SlackAlice]

Citroen C3 Stop/Start

[chas2008]

C3!..knowing Citroens history of electronic problems bet that was a reliable car.
going back to the original question though, just look at all the cars sitting in traffic jams with the engines running..all that fuel wasted..probabaly millions of gallons

[sara3]

tell your husband to stop being so tight! if he wants to save money buy him economy beer next time you're shopping :o)

[david1702198]

apparently tesco sells value beer for 12p a can!!!! tesco value lager!!!

[DungeonJayne]

"Economical" drivers bug the @rse off me.

GET A BL00DY MOVE ON !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[SCCheshire]

Great banter from everyone but no ANSWERS!!!!!! This is serious - I need to know to settle an argument! There has to be a time when it IS more economical to turn the engine off eg when you call to pick someone up and they tell you they will be a couple of mins, but my husband thinks it is a much shorter time eg at traffic lights, NOT THAT HE WOULD ACTUALLY DO IT!!!!!!!!! Are there any car mechanics out there who might know?

[shero101]

I heard that it is more economical to switch off and restart if you are stationary for longer that one minute but it's really not worth worrying about in every day traffic especially as you drive a diesel.

[david1702198]

can some local councils not fine you now for pollution if you leave your engine idling?

[NORMANTHEDOG]

turning your engine on and off,would use as much if not more than waiting for the lights to change,with it left running.

[MrBiggles]

Looks like I need to split my response across multiple entries as it errors;

The short answer to the original question is - yes. You do save fuel on switching the engine off.

A longer answer would be:
Turning an engine over, i.e. keeing it running, uses a certain amount of energy per unit of time. The amount of energy used is the same (or as shall see, very similar) whether the engine is turned over by its normal combustion power or by an electric motor (starter).

So from this notion it is reasonable to assume that switching the engine off is economical as long as it will remain off longer than it takes to start the engine again. The average modern car engine will need about 2 seconds on the starter motor to start. In theory this means that you need to leave the engine off for 2 seconds or more save fuel.
In reality we should of course allow for some losses in a: the starter motor b: the alternator. This may add up to 20% losses. That means if you need to leave the engine stopped for say 3 seconds or more (50% longer). For practiclity we can say 5 seconds(150% longer).

continued>>>

[MrBiggles]

>>>continued from above

The above is the theory why several car makers go through the trouble of installing stop-start technologies in their cars. Toyota (and Lexus) and Honda base their hybrid technologies around this function. BMW (and Mini) has spent plenty of money investing in implemting their "BMW Efficient Dynamics" technologies which includes stop-start. Many other car manufacturers also use similar methods.

While it does save fuel to stop the engine there are some aspects worth considering:
1. a normal starter motor may not be as durable as one made for stop start.
2. an engine does wear slightly for every time you stop and start it
It may very well be that these two factors are void with the modern engines and oils we have nowadays. The manufacturers who have implemented stop start seems confident enough to put this inproduction.

So conclude my ramblings I would say providing your car isn't exceptionally difficult to start and you can be bothered to switch the engine off and on, then there is fuel to be saved. Then you need to weigh that saving against whether you want to keep the pease in your house!

[SCCheshire]

MrBiggles you are wonderful!!! I knew someone out there could come up with a reasoned explanation! Thank you very much for the lesson (I had to read it twice tho' to understand it!) The only down side is that my husband was much closer to the answer than I was so I may have to keep my new found knowledge to myself!!!

[MrBiggles]

Pleased to have been of help.

I realise I did leave something relevant out of my answer.
Depending on your driving situation the amount of saving you can expect to gain from this may not be that significant. Comparing the amount of energy used by an engine on idle with an engine that accelerates (even moderately) shows a big difference. So you are only likely to see any real or measureable improvement in fuel economy if you religiously turn the engine off or a large amount of your driving is spent queueing (some real life research would be very interesting here).

But I guess as they say... every little helps!

[oldhamfan]

There are much better ways to save fuel that we're all familiar with, keeping the tyres at the correct pressure, removing all your rubbish from the boot and non-aggressive accelerating and braking!

I would suspect that any fractions of a penny saved in fuel stopping and starting the engine would be lost in wear and tear on the starter anyway.

Wife 1-0 Husband ;)