Owning a diesel car in America is definitely an unusual experience. Besides panicked gas station attendants running towards me yelling “No, miss! That pump is diesel!” and me saying “No shit, idiot,” I am most often asked if I’m worried about starting my diesel in the cold.
Along with “change your oil every 3,000 miles” and “use premium gas to get more horsepower,” the idea that diesels don’t start well in cold weather is an old myth that just won’t die. That was definitely true of much older diesels, but today’s cars are so high-tech they won’t suffer such problems. (Ask any of our diesel-driving friends in the cold parts of Europe about this if you don’t believe me. There are plenty of them.)
But we have ton of cold in Michigan right now. It was -13 degrees in Detroit this morning when I went to fire up Jolene, my trusty 2015 Volkswagen SportWagen TDI. It’s the coldest it has ever been in my life and definitely in my VW’s existence. As such, I wanted to see if my modern diesel was really up for the task, or if that old myth really had some legs.
And to make sure things were fair, I also opened the garage door for an hour, since the garage still had some residual heat trapped in it from when my fiancé came home from work the day before.
This is science we’re talking about. We’re not about to half-ass science.
But to my total lack of surprise, she started right up. As you can see, Jolene is much more reliable than her name suggests.
So how did diesels get such a bad rap?
The way newer vehicles overcome cold days is by using glow plugs, which are second only to the check engine light on my dashboard.
Glow plugs are just heated wires that work by warming both cylinder and fuel, leading to the sweet throaty grumble I’ve come to love. They’re like little space heaters for the cylinder, making the cylinder so warm it combusts easily. In the SportWagen, the glow plugs are located inside the cylinders and are powered by the car battery.
Now, glow plugs are not the same thing as spark plugs. Spark plugs are used to ignite the fumes of gasoline fuel during the combustion process. Glow plugs just warm up the compression chamber and the atomized fuel so that compression can happen almost instantaneously. Glow plugs start working before the fuel is even flowing, while spark plugs are only useful when gasoline and air are in the mix. Diesel cars, as you probably know, do not use spark plugs. Instead the engine is powered by compressing the air in the cylinder, causing the air to heat up. The atomized fuel is then injected in the cylinder and it’s the compression of gas and diesel that causes the engine to run. So while glow plugs are important for ignition, they don’t play exactly the same role as a gas car’s spark plugs.
Glow plugs have been around since the late 1920s, but it wasn’t until the 1970s when manufacturers started having luck with them in diesel car engines. Plug manufacturer Etecno1 has a weirdly comprehensive history on them, and they say the glow plugs of the 1970s revolutionized diesel engines with a—wait for it, wait for it—17 second long start time. From there the technology got better and better.
Turbo engines allowed the glow plugs to move from the prechamber inside the engine head to the actual cylinder, making the starting process even shorter. In modern diesels like mine, with the glow plugs inside the cylinders, the onboard computer can determine how hot to make the plugs and then turn over the engine automatically after only a slight delay.
So forget the diesel cold-start myth if you drive a modern one. And thank you, glow plugs, for doing the work humans don’t want to and for allowing me to enjoy my wagon—even in the depths of a miniature ice age.