An explosion and a flying cable car in downtown San Francisco are shown in a scene from the 1996 action drama "The Rock.”Reuters
My 2001 Pontiac Grand Prix blew up last winter. It was –20 C, and there was a loud explosion that did major damage to the top of the engine, shattering the ABS plastic engine cover and various components. After, the motor was overhauled: replacing plugs, wiring, oil and filter, and one module of the ignition distribution. The car now runs well. What could cause a fuel injected engine to explode in the first place? – Cameron
In movies, cars explode at, almost literally, the drop of a hat. In real life, not so much, says our expert mechanic.
"Generally, there are a few things that may cause a car to explode," says Calvin Feist, instructor at the Northern Alberta Institute of Technology (NAIT) in Edmonton. "These situations are rare, so try not to scare your readers into thinking their cars are going to burst into flames."
Feist says he'd need to know more about your car before speculating on why your car blew up last year.
"How many kilometres were on the car when it exploded? How was it running up to then?" says Feist. "Did the engine really blow up or did a part come flying out of it?"
It might be relatively rare, but motor vehicles do explode and catch fire. In the U.S. between 2003 and 2007, there were an average of 267,600 vehicle fires reported per year, says a report http://www.nfpa.org/research/statistical-reports/vehicles/vehicle-fire-trends-and-patterns by the National Fire Protection Association (NFPA). It breaks down to about 90 vehicle fires per billion miles driven on U.S. roads – and the number of fires dropped each year.
Feist walked us through some of the most common causes of vehicles fires and explosions:
Battery: "The battery could blow up, which would sound and look like the car exploded," he says. "This would normally be caused by the battery or charging system being defective." A battery blast could happen if the battery is overcharged. Also, batteries release hydrogen – freed by electrolysis of the water – when they're being charged or discharged. If a spark ignites the hydrogen, the battery could explode. "Like the Hindenburg," Feist says.
Fuel and oil leaks: If gas leaks and drips onto anything hot enough to ignite it, it'll go "boom," Feist says. Fuel leaks are usually caused by parts – like the fuel tank, fuel pump or fuel line – getting removed or replaced and not reinstalled properly. "These kind of situations are extremely rare but have been known to happen in the movies and in insurance fraud cases," he says.
Leaking oil can cause fires too. In 2009, Transport Canada recalled nearly 129,000 GM vehicles with 3.8L engines – including the 1997-2003 Grand Prix – because of the possibility of an engine oil leak that could start a fire.
Electrical: If the wiring shorts and gets too hot, it can cause a fire. "I have worked on a few vehicles that have had small electrical fires on them," Feist says. "Some of them had been modified with big stereos and extra lights that were not properly installed."
The NFPA says to look out for:
- Cracked or loose wiring or electrical problems, including a fuse that blows more than once
- Oil or fluid leaks
- Oil cap not on securely
- Rapid changes in fuel or fluid level, or engine temperature
Send your automotive maintenance and repair questions to globedrive@globeandmail.com