Q. Lately I’ve noticed my car is emitting a slight burning odor from under the hood. What could be the cause? Could it be dangerous if not fixed right away? I notice it most when driving in stop-and-go traffic.

Jackie Bowman,

San Rafael, Calif.

A. The most likely cause of the odor you’ve noticed is a fluid leak from the engine or transmission. A loose accessory drive belt also can cause an odor, but it would likely be accompanied by other symptoms such as squealing, stiff steering, poor A/C performance, engine overheating or a discharged battery.

What could be leaking? My first hunch is a faulty valve cover gasket, allowing engine oil to seep or drip downward into contact with the exhaust manifold. This gasket seals the valve cover, a tin or aluminum removable housing atop the engine’s cylinder head(s).

Most six- and all eight-cylinder engines will have valve covers, one staggered slightly to each side. With the engine stopped and cool, search around the perimeter of the cover(s), using a flashlight, looking for shiny fresh oil residue.

In most cases renewing a valve cover gasket is a minor job. Covers over V-6 and V-8 engines can be a bit more challenging to remove than that of a four-cylinder, as access can be impeded.

Other leaks are possible as well. A leaking crankshaft or camshaft seal also can release oil to a hot area, as well as a leaking oil filter, oil pressure (gauge) sending unit, or transmission seal or gasket.

Have you noticed oil or coolant leakage on your driveway? The color of the puddles and location beneath the vehicle can be helpful clues as to the source.

How critical is it to have the leakage repaired? Moderate to severe engine or transmission oil leakage to the hot exhaust system could result in a fire. Minor leakage is usually more of an annoyance than a hazard. Coolant leakage, regardless of how slight, should be looked into right away, to prevent the possibility of an engine-damaging overheat condition. I’d recommend having the car inspected.

Brad Bergholdt teaches automotive technology at Evergreen Valley College in San Jose, Calif.