You park your GLC in the garage after a drive across Dublin, and a sharp burning-oil smell drifts up from under the hood. By the next morning, the concrete under the engine is clean. On a GLC 300 with the four-cylinder, that pairing is one sign of a leaking valve cover gasket, and the clean floor is part of the evidence.

At Driven Auto Care of San Ramon, we trace that smell to where the oil leaves the engine, because on the 2016 through 2019 GLC 300 the camshaft adjuster magnets are a known leak source in the same area as the valve cover gasket. We repair whichever part is leaking, and we find it by following fresh oil back up the engine. When oil has reached the magnet connectors, the wiring comes into the job as well.

Why The Smell Comes Before Any Drip

Oil splashes across the underside of the valve cover, the cover bolted to the top of the cylinder head, whenever the engine runs. The valve cover gasket is the rubber seal between that cover and the cylinder head, and it keeps the oil inside. Years of engine heat harden the rubber until its edge no longer seals tightly.

Seeping oil doesn't fall straight to the ground, because oil that seeps from the cover above the exhaust side runs down onto parts hot enough to cook it into a thin smoke. Oil that reaches the hot exhaust parts burns off on its way down, before it can drip onto the driveway. Air moving under the car carries the smoke away while you drive. Once you park in a closed garage, the smell rises through the hood and lingers.

The oil level can also drop slowly between changes as the leaking oil burns away. Topping up brings the level back, but the leak stays in place and keeps feeding oil onto hot parts. When you call, mention any oil you've added, so we know how fast the seep is moving.

Is It Safe To Keep Driving?

A faint smell after a drive is a repair to book soon. Oil on hot exhaust parts is a fire risk, and that risk grows as the leak does. If you see smoke coming from under the hood, pull over and shut the engine off, then have it towed to us.

A Second Leak Source Beside The Cover

On the M274 four-cylinder in those GLCs, the camshaft adjuster magnets sit on the front face of the cylinder head, close to the valve cover. These magnets are small electric actuators that change the camshaft timing as you drive. Their seals are known to leak, and oil can travel from a magnet into its electrical connector.

Oil in that connector changes what the repair has to cover. That oil can wick along the wiring harness and disturb the signals the engine computer uses. This puts the inside of the connectors at the cam magnets and cam sensors into the inspection on these engines. The M264 engine that replaced it for 2020 uses the same style of magnetic cam adjuster, and leaks toward the engine wiring have been reported on it too.

Following Fresh Oil To Its Source

Old oil spreads across the upper engine, so the wet area you see can sit some distance from where the leak begins. We clean the area around the cover, run the engine up to temperature and follow fresh oil back to the highest point where it appears. Whatever part sits at that highest point is the source, and it's the part we replace.

A slow seep takes time to show, even on a freshly cleaned engine. Tracing it with UV dye is a standard way to confirm it. Under a lamp, the dye glows along the exact path the oil took, up to the gasket or the cam magnet it left from.

Tracing The Oil On Your Dublin GLC

Call Driven Auto Care of San Ramon at (925) 830-4701 when the burning smell starts. Drive your GLC over to our San Ramon shop from Dublin, and we'll follow the fresh oil back to the point where it first appears. We'll let you know whether the gasket or a cam magnet started the leak and whether oil reached the connectors.