How do cars catch fire when they haven't been in an accident?

Dear Car Talk

Dear Car Talk | Oct 01, 1998

Dear Tom and Ray:

I don't have a car, so I take the train to work every day. Between the train station and office building, my company runs a shuttle bus, which is a modified passenger van. After getting off the train this morning, I spotted the shuttle bus pulled over to the side of the road, flames leaping -- yes, leaping -- from the engine and passenger compartment, and gray and black smoke billowing out of the windows. The driver hadn't crashed. He just noticed the smoke and fire, pulled over, and got out.

Something similar happened to a friend of mine who had a used Dodge car.
I'm curious about just how such a thing can happen. How do cars catch fire?
-- Alan

TOM: Great question, Alan. We asked our Uncle Enzo, who lives in New
Jersey, how a particular car catches fire, and he said he could arrange it
for us. But I don't think he correctly understood the nature of our inquiry.

RAY: I'd say in four out of five cases, car fires are electrical fires. And
they're often caused by exposed wires that went unnoticed after an accident.

TOM: For example, someone will have an accident, and a bunch of wires will
get pinched when a fender gets dented in. The body shop will fill up the
fender with Bondo, but won't notice that some of the insulation has been
scraped off some wires. After a while, the wires start touching and rubbing
together and cause a short circuit.

RAY: You may not notice the smoke right away because you're driving 40
miles an hour, and the stuff is blowing right by you. But you're also
fanning the flames by adding oxygen as you drive. And before you know it,
everything under the hood, including the wire's insulation and all the
spilled oil, is burning, and you've got to hurry up and run to the trunk to
get marshmallows.

TOM: Sometimes short circuits can be caused by other factors: a repair job
where a mechanic connected the wrong wires together or didn't adequately
tape up a wiring job, a bad "home repair" (i.e. using the wrong fuse) or
even a factory defect in the car's electrical system. But accidents are the
most common cause of electrical fires.

RAY: Then there are oil fires. More common than gasoline fires, oil fires
can start under the hood when a large amount of oil has been spilled or has
leaked onto the hot exhaust manifold. And if the engine gets very hot or
overheats, that oil can sometimes ignite.

TOM: Of course, car fires have also been known to start at gas stations,
when people leave their cars running and a spark ignites some vapors, or
some knucklehead insists on smoking his Tiparillo while refueling. But I
assume you were really asking about non-moron-induced car fires, Alan.

* * *

Are you inadvertently wrecking your poor car? Find out by reading Tom and
Ray's pamphlet, "Ten Ways You May Be Ruining Your Car Without Even Knowing
It!" Send $3 and a stamped (55 cents), self-addressed, No. 10 envelope to
Ruin, PO Box 5541, Riverton, NJ 08077-5541.

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