Aaron Turpen: Why Cars Struggle to Start In the Cold

Automotive columnist Aaron Turpen writes, "Why does your car have such a tough time starting when the weather is cold? I can explain. In about 800 words or so. Without once using the word 'shrinkage!'"

Aaron Turpen

January 12, 20245 min read

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(Cowboy State Daily Staff)

Winter is upon us. I know this because I got my first head cold of the season. And Don Day says that a bitter cold front is coming. Which I believe since I’ve been wearing a jacket or flannel for a few days now.

This is the time of the slow, cold crank in which we sit in the driver’s seat and begin sweating (despite the freezing temps) as we wonder if the car is going to start. We then breathe a sigh of relief when it does. Then the long wait for the engine to heat up and the windows to defrost.

But there’s always that chance that the slow crank will turn into a clicking instead.

If you’ve ever wondered what is going on to make your gasoline-powered vehicle have such a tough time getting going in the cold might be, it’s not very complicated.

The first problem is the battery. Unlike the advanced batteries of electric cars, whose chemistries are less affected by low temps, the lead-acid battery still common in most combustion vehicles is deeply affected by the cold.

The lead-acid chemistry takes longer to react when tasked with power release and so less energy is sent to the vehicle’s solenoid and starter. This is why the engine cranks so much slower in the cold.

Then there’s the fuel. Unlike diesel, gasoline doesn’t turn into a viscous jelly in the freezing cold. That’s why diesel engines often have block heaters or are just left running through the cold. Some of us have not-so-fond memories of literally starting fires underneath diesel vehicles to warm up the fuel.

What gasoline does do in the cold weather, however, is take a lot longer to evaporate. Gasoline itself is not actually flammable. It’s the vapors it produces that are.

Even with the fuel injectors of modern cars, which spray the fuel to hasten vaporization, there is still less vapor in the combustion chamber when it’s extremely cold. Less vapor means less stuff to catch fire when the spark plug ignites.

Less fire means it’s harder to produce enough energy to turn the engine and keep it going. Add in that a gasoline engine only “fires” each cylinder once every four cranks (turns)--meaning it must overcome its own friction through the cycle–and it’s clear why a slower-cranking engine takes longer to get going.

Most modern vehicles attempt to overcome this cold weather phenomenon by adding more fuel when the ambient or engine temperature is below a certain point. This helps, but doesn’t really solve the vaporization problem. Instead, it just hopes that more fuel will result in more vapor. Which is generally true, but not always the case.

Putting the cold battery problem and the four-stroke engine issues with low gasoline vapor together is most of the reason for starting problems in cold weather.

Then there’s cold oil (lubricant). This can cause problems over time.

Imagine your car’s engine, bathed in oil as it runs, the oil pump doing its job and the various ports and such allowing warm oil to move around to all those moving parts and keep things lubricated.

Now imagine shutting that engine off in the driveway and leaving it overnight. The warm oil drips down the still-hot engine and into the oil pan, eventually leaving the engine mostly dry. As temperatures drop and the engine cools, that oil gets thicker. The colder the ambient temperature, the thicker and more viscous (“sticky”) the oil becomes.

The next morning, you head back out to your car and turn the engine over. It struggles, cranking slowly before finally catching and beginning to chug. It’s still cold and it won’t reach operating temperature for at least another 10 minutes at idle. Probably longer.

Meanwhile, that cold, thick oil isn’t easy to move. So the engine is running with less lubrication (likely a lot less) than it was designed for. Much of this is alleviated today by the use of much lighter weight oils.

As modern engines have gotten more compact, so have their oil viscosity needs lowered greatly. With control of oil movement in the engine being more precise and less dependent on gravity and engine heat, many of the problems with older engines in the extreme cold have been eliminated. At least where lubricant is concerned.

For most of us, the extreme cold is not a long-term issue. We’ll have a few days of it, then it will break. Then come back. And break again. Wyoming, as far north as we are, still has sunlight through the winter.

So block heaters for gasoline vehicles aren’t a necessity here. Having spent a winter in Prudhoe Bay, Alaska, I can assure you that we have it pretty good by comparison.

Our best defense against extreme cold and our gasoline-powered vehicle not starting is a good battery. As soon as your battery begins showing signs of struggle in cold starts, go get a new one. You’ll thank me for that advice when you see the next person in a parking lot begging for a jump start.

Aaron Turpen. can be reached at: TurpenAaron@gmail.com

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Aaron Turpen