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You can always count on the brakes to stop

I was taught to never put an automatic transmission in neutral when the vehicle is in motion. The other night at a party there was a discussion as to how to react if the throttle sticks open. One of the people involved, who is widely acknowledged to know about cars and driving, says the best solution is to put the automatic transmission in neutral. Others argued, saying the engine would blow up while a third group said to use the brakes to stop the car. Your thoughts? – Heather

Yes, no and yes.

The fellow who recommended putting the transmission in neutral is correct. That would prevent further acceleration. No, the engine will not blow up because there are automatic limiters on most modern engines to prevent this from happening. Yes, the brakes will stop the car. Even if you do put the transmission into neutral you will still have to use the brakes to stop the car.

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When training instructors, we show them how to take control should a student panic or freeze up and a crash appear imminent. Among other things, it may involve flipping the transmission into neutral. But it is important to realize the brakes will still stop the car.

I've done some instrumented testing on a variety of cars to determine if the brakes will overpower the engine. In every single case with the throttle held wide-open – i.e. my big, heavy right foot pressed firmly into the carpet – the vehicle was brought to a complete stop from 100 km/h with the brakes. It took approximately 5 to 8 per cent longer than without the open throttle – or with the transmission in neutral. But the brakes will stop the car.

Two added thoughts here:

  • Despite all the media attention, throttles very rarely stick open. Research after these well-publicized incidents has consistently proven the driver had pushed on the throttle when they thought they were using the brakes.
  • I am a firm believer that regardless of what we are taught, the average driver will revert to a sudden and violent application of the brakes in an emergency situation, unless he or she has repeatedly practiced any other method. For example: It is great to teach people to look and steer in the direction of intended travel when dealing with a skid. But that same driver will automatically slam on the brakes and stare at the threat when surprised by a loss of grip. For this reason alone, I believe ABS and stability control to be the most significant safety advances in the last half century.


I've rear about turbocharged engines and often there is mention of intercooling in the same sentence. What is that? – Graeme

An intercooler is a device – a radiator of sorts – used to cool the air the turbocharger is forcing into the engine.

The turbocharger consists of two sides with an impeller or set of blades on each connected by a common shaft. The exhaust gases leaving the engine turn the blades on one side, which causes the blades on the other to turn as well.

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Some of the heat from those exhaust gases is transferred to the intake or cold side. An intercooler is used to lower the temperature of that intake air. This increases the density of that air, which results in more power, because more fuel and air can be squeezed into the same area (combustion chamber) to be ignited.

Intercoolers can be air- or liquid-cooled, but air-to-air is almost universally used on production vehicles. In most cases the intercooler is a second radiator placed directly in the air flow separate from the coolant radiator.

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