Why Are So Many Parked Cars Catching On Fire?

When I was about nine years old, I was riding in the back of my family’s old ’68 Volkswagen Beetle when the car started to lose power and slow down. My mom, who was driving at the time, began to pull over to the side of the road, and at that moment I looked behind me, out the back window, to see an ominous column of smoke emerging from the back of the car. That was my first car fire!

And while I haven’t really had a full car fire since then, I have had plenty of cars that seemed more than willing to give fire a chance. A Volvo P1800 with twin SU carbs that loved dumping fuel on a hot exhaust manifold, brittle fuel lines hiding under braided fabric covers just waiting to drip onto a hot muffler, and so on. Basically, when it comes to older cars, they almost always seemed like it wouldn’t take all that much to get them to ignite, really.

Except, of course, for when they were off. And that’s what’s so different about what’s happening now to over 3.2 million cars that have been saddled with NHTSA “park outside” warnings. Because those cars, be they Jeeps, Kias, Hyundais, Chryslers, BMWs, and more, are all at risk of catching on fire while they’re off. So what the hell is going on?

Well, I talked about this in at least a little bit of detail with Flora Lichtman of Science Friday, who was kind enough to give me some leeway to rant like the cranky old bastard that I am:

That’s the whole episode, which includes a compelling interview with a food safety expert, for those of you interested in avoiding long, languorous drives down the Highway of Hershey, but if you want to be rude and just jump to the segment about cars, I guess you can jump to timestamp 14:18.

If you’re opposed to listening to that at all and prefer to listen with your eyeballs, using an exotic technique called “reading,” then I suppose I can recap the essence of what I was going on about.

So, why are all these cars catching on fire when they’re not even on? They’re all fuel-injected, so no leaky carbs, and they’re all relatively new and modern – you’d think this would be a very solved problem! But the problem is more complicated than it seems, and it’s from our own doing, really. The reason cars are catching fire when off and parked is mostly because modern cars are never really “off.”

If you want your car to, say, detect your keys when you approach and illuminate its lights seductively and unlock itself, or protect itself from intruders when it’s parked, or use its cameras, or get over-the-air software updates or any number of other things cars do when not being driven, then you have to accept that your car is still on, at least electrically, when it’s been turned off.

The engine may be off, but modern cars still have plenty going on, powered by their 12V battery (or a larger battery in the case of hybrids or EVs), meaning that there are many, many circuit boards and wires crammed deep within these cars that are hot, electrically. And components in cars are packed together incredibly tightly, especially in the case of hybrids, which means that there’s a lot of opportunity for parts and fluids and other bits to interact in unexpected ways.

For example, the issue with Jeeps has to do with the power steering system, an Electric Hydraulic Power Steering Pump (“EHPSP”), that can have electrical connections of very high resistance that can generate heat, and it’s close enough to other components that it can catch things on fire. The Kia recall is focused on a power seat motor that can be stuck on and generate heat and set things on fire, others have wiring that is hot and in the path of potentially dripping brake fluid that can cause a short and create sparks or resistances that can set things on fire, and so on.

While these details differ, the fundamental causes are all essentially the same: cars that are “off” are full of flowing electricity, and whenever you have that near flammables like fuel, a risk of fire exists.

If all this makes you nostalgic for a time when you turned a car off and it was really “off,” you’re not alone. But, like so much in life, we’re here because of tradeoffs and compromises. You want the convenience of keyless entry and security systems that work? Then the car needs to run sensors and computers and RF transceivers and more while parked. The reason we haven’t seemed to fully solve the problem of keeping cars non-aflame while parked is because we’re constantly making the problem harder.

Of course, that’s no excuse! Car makers should absolutely be able to make cars that don’t spontaneously combust while just sitting there! That feels like a pretty mild ask, really.

Anyway, thanks to Science Friday for indulging my ranting.

Top graphic images: Stellantis; DepositPhotos.com