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Turn off the engine

Have you noticed that quite a few of the car manufacturers have brought out cars which turn off the engines to save fuel under certain conditions?  BMW I think were the first to start marketing these.  There is actually quite a complicated computer program involved to make sure the engine is not damaged or will restart.  For example, it won’t cut out below certain temperatures, or when the battery charge is below a certain voltage.  It also checks the engine temperature as well and all parameters before cutting out or not.

This has really got me thinking.  Is this a proper way to save fuel?  What about the extra fuel required to restart?  Does it actually help to reduce pollution?

Apparently there have been loads of research about the cost of letting the engine idle.  The point at which fuel is saved is about ten seconds for a typical family diesel car and eight seconds for a petrol verison.  The times reduce by 25% if air conditioning is turned on as well.  So in pure fuel terms, turning off the engine sounds good.

Just think of all of those 6-8 seconds when the engine was left idling.  Do you, as I do, start the car and then put the seatbelt on, adjust the radio and do other things before moving off?  I’m going to try to be more aware of the idling time for my car.

Waiting at railway crossings is a very obvious place, but you have to make a judgement about how long you are going to have to wait.  But there are clues, did you see the gate/barrier closing?  Are you first or near the front of the queue?  Chances are that you’ll be waiting much longer than 8 seconds.

Traffic jams and accidents, it is actually quite rare that you’ll be in a traffic jam, where the traffic is stationary for long periods.  Usually it just creeps along and that is no help.  But I’ve certainly been behind accidents, where nothing moves for ages while a vehicle(s) is recovered.  In fact the average normal traffic lights cycle can take much longer than 8 seconds.

Doesn’t it make you think?

What about wear on the starting components?

It takes a lot of power to start a car’s engine, and with that in mind, it is only natural to question whether “unnecessary” restarting is a good idea.  The extra strain on the starter motor, the battery, ignition and the fact that oil will have begun to drain back into the sump.  Also, as mentioned above, the leading car manufacturers have quite complex programs to decide when and more importantly when not to stop their engines.

I am not an expert by any means and therefore, I don’t feel qualified to answer the above question.  But I would not recommend going over the top or becoming obsessed with this.  I’m really suggesting a few extra starts per week.  I can’t imagine that a few extra starts would make that much difference.


  1. Stop start technology is becoming popular
  2. Manufacturers use tight parameters to control stop/start
  3. A car uses more fuel when idling for 6-8 seconds than a restart
  4. There are lots of times when we all idle our cars for much longer than 8 seconds
  5. It probably does wear out some components faster
  6. Don’t over do this

I’m certainly going to give this some more thought and think more carefully about the situations when I leave my car ticking over.  I really suggest you do the same.  After all fuel is now at a record high in terms of costs.  If we add this to the other well documented advice, we might all save.

Good for your wallet, good for the environment and not so good for the fuel companies.

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