Joint 7 On Your Side / ABC Investigation: Experts struggle to find cause of non-crash car fires

SAN FRANCISCO (KGO) -- A joint investigation by 7 on Your Side's Michael Finney, ABC's Brian Ross and a team of ABC reporters has found reports of dozens of fires across the country in the last five years.

In two fires we identified in San Francisco alone, combined property damage was estimated to be $200,000. Why the fires started in the first place remains a mystery.

It was just three years ago that one such fire broke out in San Francisco. Darla Edwards says she and her 6-year-old son, Antonio, were fast asleep when a neighbor banged her gate. She looked out her bedroom window and says she discovered the front of her 2001 BMW SUV on fire.

It blew out big portions of the hood and windshield. Intense heat melted portions of the front grill.

"I just saw some flames and then when my mom started crying, I start crying too," said Antonio.

His mother remembers flames as high as the middle of the letters on a stop sign.

"It was doing like a 'pop' noise, like 'pop pop pop' - as if something was going on under the hood," Edwards said.

Her neighbor, Arthur Emerson, was the first to spot the fire and alert Edwards.

"I was mostly afraid it was going to blow up myself. That's why I tried to react real quickly," Emerson said.

Damage to Edwards' BMW was estimated at $9,000. She said BMW offered her $2,500 toward the purchase of a BMW, but she declined the offer.

Part of an iconic group of historic Victorians in San Francisco's Haight-Ashbury was the scene of another fire just 15 months earlier.

A 2007 BMW SUV was parked in the driveway when it erupted in flames. Firefighters say it started on the hood of the vehicle. The heat was so strong, that the BMW's engine dropped to the surface of the driveway.

Flames quickly leaped to the home next door. A mother escaped with the couple's two children, who were 7 and 8 years old.

Both families declined to talk on camera.

Total damage to the two houses and the 2007 BMW X3 was estimated at $190,000.

Nearly 600 2007 X3s were recalled in 2012 because an aftermarket part for the motor on the engine cooling fan could overheat, possibly causing a fire. ABC7 News was unable to determine if that recall included this particular car.

According to investigators, both this fire and the one that destroyed Edwards' car are believed to have started in the engine compartments.

The battery in her BMW had recently been replaced prior to the fire. She told investigators a power issue with the ignition interlocking device caused the battery to discharge.

Arson is not suspected in either case. Electrical failure has not been ruled out.

In addition to the fires in San Francisco, our team from ABC found dozens of other parked-car fires in some new cars, as well as older cars. Some of these cars were under recall for non-crash, fire-related issues. But most were not.

Experts tell us the age of the cars, issues about maintenance records and where the cars were serviced make determining the exact cause of the fires difficult.

One expert says the fact that cars are never really off might be an issue.

"When a car is off, and it catches fire, obviously you have a problem and most of the time they're coming from an electrical system," said Sean Kane of Safety Research and Strategies. "A lot of power to these electronic systems is going to remain on in the vehicle even when the vehicles off."

The automaker said, "We have investigated, and in some cases, inspected the vehicles identified by ABC News. These vehicles span an age range of one to 15 years. We have not seen any pattern related to quality or component failure. Vehicle fires can result from a wide variety of external issues unrelated to product defect."

Such external factors could include poor maintenance, aftermarket changes and even rat nests.

ABC's Brian Ross asked Kane if the answer to the cause of these fires was somewhere in there.

"The answers going to be there, sure, sure. And you know it may not be an answer. It may be many answers."

The National Highway Traffic Safety Administration says, at this time, there is no evidence pointing to a safety defect, but is urging anyone who's experienced a non-arson related, parked-car fire to report it to them.

Brian Ross will have a lot more on this investigation later tonight on Nightline.