M273 5.5/4.7L Engine - In-Depth Look at Design and Reliability (2024)

The 5.5L and 4.7L V8s are completely aluminum engines. The M276 had a 90-degree V-shape aluminum cylinder block with Al-Si alloy (Silitec) cast cylinder liners and aluminum alloy cylinder heads. Inside an aluminum crankcase, there is a forged steel crankshaft secured by reinforced bearing caps. The engine is equipped with fracture-split, forged connecting rods and light-weight, low-friction aluminum pistons. The engine block of 4.7L M273 46 KE has 92.9 mm (3.66 in) bores and an 86.0 mm (3.39 in) stroke. The 5.5-liter version (M273 55 KE) has 98.0 mm (3.86 in) bores and a 90.5 mm (3.56 in) stroke. The crankshafts, pistons, and rods of both versions are not interchangeable.

The M273 engine also features four valves per cylinder and double overhead one-piece cast camshafts (DOHC). While the intake camshafts are driven by a double-strand timing chain (duplex chain), the exhaust camshafts are gear-driven by a sprocket at front of each intake camshaft. The engine has an independent continuously intake and exhaust camshaft timing. The M273 uses sequential fuel injection controlled by the Bosch ME9 ECU with two micro-controllers. The cooling system is also managed by ECU - a mechanical thermostat was replaced by a new electronically controlled thermostat for optimum control of engine temperature. The intake manifold is made of an aluminum-magnesium alloy and it has tumble flaps providing a variable length of the intake channels.

In 2010, as a replacement for the M273 engines, Daimler AG introduced the 4.6-liter V8 twin-turbocharged Mercedes-Benz M278 engine.

Engine Specs

Mercedes M273 Engine Problems and Reliability

Unfortunately, the M273 engines have earned a reputation as one of the most problematic Mercedes V8 engines. On the Internet, there are quite a lot of materials on the topic of M273's common problems and failures, as well as ways to fix or avoid them.

A weak place is engine timing. Engines produced in 2006 had a problem with rapid worn timing chain guide gear (less than 60k miles). This failure could cause a wrong positioning of the camshafts. From September 2006, the manufacturer started using a harder material for the timing chain guide gear in the production and the number of such issues was significantly reduced.

A cam plug oil leak is another widespread problem of this engine family. This is typical for engines manufactured before June 2008. Oil leakage was on the backside of the cylinder heads from the round expansion plugs made of plastic material. Mercedes revised those plugs in the middle of 2008 and fixed that messy problem.

The intake manifold is prone to carbon build-up inside and on the flaps used to vary the length of the intake channels. Dirty flaps could be stuck or create high loads on the plastic VIM actuator cam. In both cases, that will lead to actuator cam breakage. Incorrect operation of the variable intake manifold features the following symptoms: rough idle and a loss of power with check engine light illumination.

Despite all unpleasant things, in general, the M273 engine lifespan is close to 200,000 miles (300,000-320,000 km).