What causes Car Fires?

Every few days on the traffic station, I hear of a “traffic jam due to a car fire”, which I take to mean where a car catches on fire without some external cause (accident, etc.) The other day I happened to see one in progress - a car, just parked on the side of the highway, engulfed in flames.

In a certain way, it’s not surprising to me that this happens. After all, a car is full of various flammable liquids, around which we purposely set off thousands of explosions per second. It’s actually somewhat amazing that they don’t catch on fire more often.

But it struck me that the burning car I saw was a recent model and didn’t externally look like a beater or anything. Now it has me looking at my car thinking “So, what does it take to set one of these things off?” I’ve never seen anything on car maintenance that says: check your X every Y miles, if it develops a Z it might result in a fire.

Is it generally an electrical problem? Timing problem causing a misfire? Excess friction on moving parts? Gas Leak? Oil dripping on a hot exhaust? Etc.?

Oil leaking onto the hot exhaust is a biggie. It can be a steady seep that finally hits critical mass on the one day that someone takes their grocery getter onto the highway for a long drive, or a sudden squirt out of a blown hose or fitting - nearly lost one car myself when the power steering line blew. Happily (?) I was half a block from home and a fire extinguisher when it happened, so the only lasting damage was a mess on the street and fire extinguisher powder everywhere.

User stupidity is another - I saw a car come to smoking badly after the driver topped off the oil, but forgot to put the filler cap back, so oil was splashing out.

I’ve also seen cars catch fire from the actions of animals. I saw one car that had a bird nest in the air cleaner, judging by the remnants of charred twigs that were in there. Another car was the unfortunate victim of a squirrel that jammed nuts into (again) the air cleaner.

I had a Buick Skyhawk catch fire once. Apparently, a part of the EGR system broke loose and allowed hot exhaust gas to impinge on grease-covered plastic parts. No doubt that exhaust issues are the main reasons that cars catch fire. I’ve heard of cars catching fire from parking on top of dry leaves–the heat of the exhaust pipes is enough to touch off a blaze under the right (wrong?) conditions.


In each & every case that Phlogiston has been placed inside a car, it has caught fire.
Darnedest thing.

Lots of things cause car fires. In no particular order
[li]electrical short circuits[/li][li]Engine oil leaks[/li][li]A/C leaks (the lube oil is flamable)[/li][li]Power steering leaks[/li][li]foreign objects (rat nests, bird nests, etc)[/li][li]Converters can overheat and radiate enough heat to set something else on fire[/li][li]You can can run over or park on a flamable item and the exhaust can catch it on fire.[/li][li]Craptacular accessory installation casues and electrical short circuit and causes a fire.[/li][/ul]
hose can crack and leak. Hose can get holes rubbed into them. nests can get built on things that get real hot. Wires get damaged and short out.

Older cars used to have the fuel pump on the engine, and they “sucked” gas out of the gas tank. If the fuel line ruptured, you could get a fire since some fuel would go splattering, but mostly the fuel pump would just start to suck air. On a modern car, though, the fuel pump is inside the gas tank, and if the fuel line ruptures, the pump continues to spray fuel all over the place. If fuel sprays on something hot (exhaust, hot engine block, etc) you’ve got plenty of opportunity to start a fire.

My mother in law’s Dodge van was good at blowing its fuel line. It did it three times before she finally got rid of it. Fortunately, nothing caught fire. I believe Dodge ended up recalling a bunch of vans and trucks because of the problem.

Many years ago, I was coming home from a college class and a car pulled off the road ahead of me. I stopped to see if they needed help, and they had some sort of electrical fire inside the car. When they first stopped, they just had a bunch of smoke inside the car. A couple of minutes later, the car was comlpetely engulfed in flame. It’s amazing how fast a car goes once it starts to burn.

The catalytic converter on my truck got clogged a couple of years ago (just due to old age, and the honeycomb inside started to fall apart and blocked the exhaust). One of the tubes on the EGR valve assembly broke and was spewing hot exhaust gasses into places where hot exhaust gasses weren’t supposed to go. Melted a bunch of plastic, but fortunately, no fire. With all the wiring in that area, though, I guess I just got lucky.

We had an unusual car fire here a couple of years ago. It was an early winter morning and a semi tanker hauling LOX tipped over on a freeway off ramp. Those tanks are pretty well designed and shouldn’t leak in a simple accident like this one, but this one did.
There was a cloud of LOX/air mix spread out from the tank. A woman in a late model SUV ran through the mixture while using a nearby on ramp and her car stalled, authorities speculated that the engine sensors detected the oxygen rich air and increased the fuel flow, stalling the engine. I have no idea if this could be correct, but that was on the news. When she tried to restart the car she heard a loud pop and then saw smoke. Fortunately she got out and then saw flames and moved away from her car, which was fully engulfed in a matter of minutes. Fire apparatus was already on the way to the truck rollover so they arrived very soon, but even then it was too late for the car.

Design flaws can’t be overlooked. The PT Cruiser (2001-2002 I think) had a fuel line that rested in the engine compartment in such a way that the motion of driving would wear a hole in it. Fuel fire ensued.

Other causes I’ve seen include: plastic bag/litter hits a hot catalytic converter and starts burning; sparkplug wire fails/disconnects and that cylender starts flushing fuel into the exhaust system; poorly installed/adjusted carbureator; mounting screw bored through high-output stereo wiring; short circuits under the dash caused by age/manufacture/handyman modifications…Mostly electrical and fuel are the causes, naturally. And since those are some vast systems in a lot of cars, there are plenty of places for something to go wrong.

I had my old '86 4-beater Mustang catch fire one time. Ironically, it was while I was on the way to the mechanic’s place to get the engine looked at. Far as we can tell, some gidget inside the car dissappeared (no idea WHERE it went, it just ceased to be there) and we had our mechanic drive out to our house to replace it. For whatever reason, he didn’t do a test drive (I’m not even sure if he normally did house calls, he might have just done it because we were a frequent customer of his) and so the next time I drove it, the timing was all wacked out, with the engine rattling along noisily while I cruised at a break-neck speed of 20 miles per hour on the access road.

A block short of the access road, my dad (driving behind me) starts blinking his lights and tapping the horn at me, but since we’re a block from the mechanic’s shop, I just keep going and then pull into the lot. Apparantly my dad saw smoke billowing out from under my car, and as soon as I parked, it started billowing out from under the hood (which is when I first noticed it). I pop the hood, and soon after the engine compartment is a-burning, and my dad and I extinguish it by gathering up hands ful of dirt and gravel from the parking lot and tossing them into the engine compartment.

We get the car back the next day, and it runs like a charm. Apparantly all we needed to do to make the damn thing work right was to adjust the timing and then set fire to the engine, thus melting and/or burning away three or four un-neccesary components such as the air intake hose the breather box, and the insulation on the inside of the hood.

I think it was 3 or 4 months later that finally the car blew a piston on the one icy day of the year in Dallas and left me stranded at school, so we gave the car to our mechanic as a “get this damn thing away from us” gift (I wanted to sieze the oppertunity to rip out the old 4 cylinder engine and replace it with a V6 and a working air conditioner, but my parents veto’d the idea).

IIRC, this has also been the cause of a number of plane crashes as well, since on many large jets they run the electrical wiring through the fuel tanks as an efficient way to keep the wiring cooled (amusingly enough, to prevent fires). That’s not a problem unless the fuel level gets low enough in the tanks that the wires come into contact with fuel vapors (as opposed to liquid fuel, which is relatively inert, from what I understand). When I took ground school so many years back, while we were learning about circuit breakers on airplanes, our instructor made it a point to tell us a story about some Air Force jet that blew up because some guy reset a tripping circuit breaker too many times (IIRC, you’re supposed to reset it the first time it trips, then if it trips again, leave it tripped). He seemed to have a different story about a plane crash to go along with a LOT of the stuff we were learning about (which I suppose is what happens when you fly bombers for 20+ years).

Also along the lines of design flaws, ISTR the Ford Pinto is rather notorious for it’s tendency to burst into flames if it was rear-ended in traffic. The Ford Crown Victoria police cruiser has also had some fire problems, though in that case I’ve heard it may have been due to accessory mounting screws used to attach police equipment penetrating various things they shouldn’t inside the car.

Wires run through the fuel tanks to keep them cool? :dubious: This is not the case on airplanes built by the large commercial jet airplane company I work for.

Maybe cars containing the deadly phlogiston should by law be filled with dihydrogen monoxide to counteract it’s deadliness.

First off fuel vapors by themselves are not dangerous. It is when fuel vapors are mixed with oxygen in the correct ratio that they become dangerous. Very dangerous.
Next I doubt that anybody would run electrical wires through a fuel tank except for what was needed for the level sensors and pumps. Why in the world you you need to keep electrical wires cool? If you are running so much current through them that they are getting hot, you need a larger wire. Duh.
Lastly a fuel tank on an airplane is way different enviroment than the fuel tank on a car. As the plane acends and decends the pressure changes in the tank drawing oxygen into the tank (and the tank has to be empty for this to be an issue) Then if you manage to get just the correct ratio of air and fuel in the empty tank AND you get a spark, the airplane goes BOOM. This is what probably caused the TWA flight 800 crash.
so the differences are:
[li]Cars don’t routinely climb and decend to 30,000 feet[/li][li]Cars don’t drive around with empty fuel tanks.[/li][/ul]

You’re not a were-charizard by any chance are you? Had any weird dreams lately?

[slight hijack]Heh, I did this to my Mustang, only it was a '74 and the engine I shoe-horned in there was a 289HP out of an old Galaxy. I could spin the tires in the first three gears.

Just to add another data point, a friend of mine’s car caught fire when an improperly-fixed fuel line leaked onto something hot (presumably the exhaust).

And another data point: I was watching one of those COPS-style shows on CourtTV last night, where a car had caught fire because the driver fell asleep at the wheel.

With his foot on the gas pedal. :eek:

There was a wall in front of the car, preventing it from moving anywhere, and friction took its toll.

Result: roasted car and rather shocked driver. It was mentioned the driver fell asleep because of some medication they were on.

<< Who’s General Failure & why’s he reading my disk? >>

It happened to two friends of mine. One had a gasoline leak where the fuel line hooked up the recently rebuilt carburetor. At a stop light, the vapor-to-air ratio was finally right, and it lit up. It burned everything from the dashboard forward. He didn’t have fire insurance. I asked him, “Who rebuilt the carb?” He had tears in his eyes as he said, “My dad.” :smack:

By the way, if you ever have a car fire, don’t try to rebuild it. It’s a nightmare, and the wiring will never be right.

The other fellow threw a cigarette butt out the window of a convertible just before he got to a shopping mall. When he got back to his car, he saw the FD putting it out; the whole interior was gone. His cigarette had blown back into the back seat.

There are also cases of people carrying extra fuel cans and incompatible products carried in the vehicle. I was following a fellow who had pool chlorine in his trunk (he’d forgotten about it) and the cardboard container became wet with a leaking container of brake fluid. Smoke seeping from the trunk lid and back seat immediately preceded his meeting with the big dog-WOOF!

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