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you & your car

I'm hoping you can settle a disagreement I have with my fellow taxi drivers regarding whether it is better to leave the taxi running solid without turning it off in a standard 12-hour day shift. On average, the drivers who turn the car off and on will do so about 30 times a shift. My argument to leaving the car running solid during the shift is that it is less wear and tear on the engine and all other moving parts than if you turn it on and off between fares. I know there is a carbon footprint to doing this and also increased fuel costs (actually, the fuel cost is minimal; I kept track doing it both ways, and I would argue that every time you start a car there is a large output of exhaust so the carbon footprint is also minimal). Another reason I prefer to keep my taxi running is all the electrics with the onboard computer dispatch screen, taxi radio, roof light, etc. This is a drain on the battery when the car is off and, if you don't keep track of the time that the car is off, the computer system shuts down when the voltage level gets too low. This means you have to reboot after starting the car up and you lose your position in the rundown and go to the bottom of the pack and maybe wait an hour to get a fare. I would be grateful for a definitive answer to settle the debate. – Don in Brampton, Ont.

Ah – the great debate! And a request for a definitive answer! The two are at odds.

The fact there is much debate is a result of the lack of a clear answer. My answer? If idling for more than 15 seconds or so, shut it down.

But there are a number of factors that would cause me to alter that view, not the least of which is your business information system shutting down after a set period. I'd address that by learning what that time was and using a timer of some sort to remind you to restart the engine.

Generally speaking, the issue is one of exhaust gases and their effect on the environment. An idling engine is consuming fuel and producing harmful emissions. Not much in comparison to engines of the past, but there is a carbon footprint.

Older carbureted engines required a great deal of raw fuel and battery power to start. Stop-start systems would not have worked with them. But modern engines with electronic control systems use very little fuel and draw very little from the battery on a normal start, especially when the engine is warm.

Tests show that an idling engine, depending on size, uses between 0.025 and 0.05 litres of fuel per minute. For every minute of idling you use enough fuel to go about one kilometre. Idling for more than 15 seconds or so will use more fuel than restarting the engine.

Throttle response

I suppose my 1996 Toyota Camry accelerator mechanism was a traditional mechanical system but I believe my present 2009 Toyota Corolla is a "by-wire" system for the accelerator. I found one had to have a very soft touch on the pedal to avoid starting with a jerk. – John

The difference you notice is not due primarily to the difference in throttle control systems, rather in the way they are set up.

Many manufacturers "dial-in" an inordinate amount of throttle input to the initial pedal application. For example, the first 10 per cent of pedal travel – whether by wire or cable – may result in the throttle opening 25 per cent. This gives the impression of lots of power – but it is obviously a false impression as the remaining 90 per cent of pedal movement yields only 75 per cent of available power.

Correction: An earlier online version of this story contained incorrect information about the use of fuel while idling. This has been amended.