Q: My 2008 Toyota Camry Hybrid has been giving off an odor of mildew or mold since last November. The dealership couldn't find what was causing this issue, nor could an independent auto repair shop. I did find dampness on the mat behind the driver's seat. I cleaned and dried it and put it back in, but it hasn't helped. The trunk does not smell moldy.

S.S., Chicago

A: If the dealership and shop both eliminated the air conditioning system as the source, there may be a small water leak into the interior. You will have to find the source of the leak, but that is not always simple. We once owned a pickup that leaked from a seam at the back of the roof and water puddled in the driver's foot well. After the leak is fixed, find a detailer with an ozone machine. Detailers are often located in conjunction with full-service car washes. The ozone should eliminate the smell, but if it comes back, you may have to hire Sherlock Holmes.

Q: I leave my 2010 Subaru Forester in my New England garage for three months and have a friend start it up, roll it out of the garage for 10 to 15 minutes once a month while I am away. You recently mentioned a battery maintainer. Can you explain? My friend found the battery dead this past week after two months in the garage.

K.S., Simsbury, Conn.

A: A battery maintainer is simply a battery charger, or trickle charger, that turns itself off when the battery is fully charged and then back on as needed. Continually charging the battery after it reaches full will damage it. A battery maintainer will switch itself to a "float" mode and keep the battery from both over- and undercharging.

Q: Recently, my wife's 2003 Toyota Highlander passed 150,000 miles. No sooner had it done that than the timing belt snapped and, in so doing, damaged and froze three pulleys and knocked out the water pump. Our longtime service person repaired the damage and said it could have been worse had the car not had a "noninterference engine." The internal engine parts were not damaged despite the severity of the occurrence. He further indicated that if our vehicle had an "interference engine" he'd be telling us that the engine was totaled because such damage to an interference engine would wreak havoc on the inside of the engine as well. Since the repair, the Highlander runs perfectly. Can you please explain more about interference versus noninterference engines, and how one can tell which kind of engine is installed when purchasing a vehicle?

P.M., Deerfield, Ill.

A: A noninterference (free-running) engine will not be damaged if the timing belt breaks. Despite the valves being out of sync with the pistons, these components will not collide with one another. There is adequate space between them, even when the pistons reach top dead center. Interference engines, on the other hand, have little space, so if the belt breaks, valves and pistons crash into one another, bending the valves and damaging the pistons. Fixing the damage is expensive. The simplest pre-purchase tack is to ask the service manager.

Bob Weber is a writer and mechanic who became an ASE-certified Master Automobile Technician in 1976. He maintains this status by seeking certification every five years. Weber's work appears in professional trade magazines and other consumer publications. His writing also appears in automotive trade publications, Consumer Guide and Consumers Digest Send automotive questions along with name and town to motormouth.tribverizon.net.