Engine heat: a math lesson that could save your life this winter

Easy numbers to calculate how long you can idle if you need your car to heat up

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Let’s turn your car’s fuel gauge into a clock.


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Weird, isn’t it?

But consider this: do you know how long your car’s engine can run on one liter of gasoline? And do you know how much gasoline is in your car’s tank?

If you do, you are a very simple math lesson away from being able to calculate how many hours of heat you can generate from your vehicle’s current fuel supply during survival idling – that is. ie running your engine to keep you warm if you are helpless or stuck in the cold and trying to stay alive until help arrives.

Whether you experience a mechanical breakdown, an accident, or any other setback that gets you stuck in the cold, this little exercise can help you navigate more serenely by removing an important unknown from the situation: How long can you stay warm?


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Two caveats before our math lesson. First, it applies to modern fuel injection gasoline engines. Second, nothing I’m about to explain is more important than being properly prepared for winter driving emergencies, which includes keeping emergency survival equipment and supplies working in your vehicle. at any time.

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Here is the calculation:

Take the displacement of your engine in liters and multiply by the number 0.6. The resulting number is the number of liters of gasoline your car needs to idle for an hour.

Take the Lexus IS300 AWD for example. It has a 3.5 liter engine. Multiplying 3.5 by 0.6 gives us the number 2.1. That’s about the number of gallons of gasoline you need to generate an hour of survival heat, by idling the engine. In other words, every hour of engine operation to warm up reduces the fuel level by 2.1 liters.


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Now let’s turn the fuel gauge into a clock. For this you need the size of the fuel tank. It’s a quick web search, just like your engine displacement, by the way.

The Lexus has a 66-liter fuel tank and every hour of heat consumes 2.1 liters of fuel. If we divide 66 by 2.1, we come to the number 31. This is the number of heating hours you have, if your fuel tank is full. From there, check your fuel gauge. Half full means about 15 hours of heat. A quarter of a tank means less than 8.

Toyota's winter event
Toyota Canada Photo

In a GMC Yukon with the 6.2 liter engine, the calculation gives us 6.2 x 0.6 = 3.7 liters per hour of idling. With a tank of about 91 liters, that’s 91 / 3.7 = 25 hours of heat on a full tank.

Ford Mustang with 5 liter engine and 61 liter tank? The calculation gives us 3 liters per hour of heat, and about 20 hours of heat on a full tank.


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So if you drive something sporty – say, with a big engine and a smaller fuel tank, your clock can have relatively less idling time, compared to something with a smaller engine and a smaller fuel tank. (relatively) larger.

For example, the Honda CR-V. With a 1.5 liter engine, that’s less than 1 liter of fuel required per hour of heating. If its 53-liter tank is full, that’s good for 59 hours of heat.

So whether your car has a big tank and a small engine, a small tank and a big engine, or something in between, you now know how to do the math on your own, eliminating a stressful stranger if you ever find yourself struggling. get stuck in the cold. Think of this as your annual reminder to keep those fuel tanks (and batteries) full for your winter trips.


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