Mercedes-Benz C-Class (W203)

Mercedes-Benz C-Class (W203)

This isn鈥檛 unusual. Often, newly released products have some problems. It takes a while for the manufacturers to sort out design flaws and quality issues. This is true not only for cars but many other products. A bit of an extreme example is the Samsung Galaxy Note 7 with its batteries catching fire. In my opinion, corrosion was one of the top problems with Mercedes-Benz vehicles produced between 1993 and 2004. This is because around 1993 Mercedes-Benz implemented a more environmentally friendly, water-based paint. Only in 2003/2004, Mercedes-Benz started galvanizing their cars, which improved the corrosion resistance significantly. Therefore, I recommend getting one of the post-facelift W203 models as they all have galvanized bodies. The facelift took place in 2004 (2005 in the US). The early W203 models, manufactured before 09.2003, might have been fitted with radiators that can cause expensive automatic transmission failures. The transmission oil cooler in these cars is integrated with the radiator. The faulty radiators were made by Valeo and had a problem with an internal seal that was supposed to separate the coolant from the transmission oil. A failed seal would release the coolant into the transmission oil circuit.

This oil/coolant mixture can ruin the transmission if not flushed quickly. Cars with manual transmissions are not affected. The coolant in the transmission is not a good thing and causes severe clutch surface wear, among other issues. The typical symptoms of a failing radiator seal are harsh gear changes and humming/droning noise during light acceleration up to 2500 RPM. The majority of the C-Class vehicles on the road today would have had the faulty radiators replaced by now. If you do buy a car with a Valeo radiator, consider having it replaced as there is still a small risk that it could fail. It鈥檚 much cheaper to replace a radiator as a precaution than it is to replace a dead transmission. Only cars manufactured before 09.2003 are affected and newer Valeo radiators are fine. You can identify a Valeo radiator by the crimping method i.e. how the metal core is joined with the plastic sides. In my opinion, the head gasket is the weak point of these engines.

Considering head gasket replacement is inevitable at some point, often around 150k miles. Before the gasket fails completely, these engines often develop an external oil leak from the head gasket at the back of the engine. Make sure to inspect that area when buying one of these cars. Once the head gasket fails and is replaced, the new one should be good for another 100k - 150k miles. This issue mainly affects the inline-6 engines, because of their long cylinder heads. However, the 4-cylinder M111 engines are also affected, but to a smaller degree. These engines are fitted with superchargers. The superchargers are reliable but have a finite lifespan. I estimate that they will need to be rebuilt after around 150,000 miles. The engine and other components under the bonnet will last a lot longer, so it鈥檚 very likely that the car will need to have the supercharger rebuilt or replaced at some point during its lifetime.

Generally, when a timing chain is used, the intention is for it to last the 鈥渓ifetime鈥?of the engine (very roughly 200k miles). Leaving it for this long in the M271 engine is very risky, in my opinion. There have been cases of premature chain stretch in these engines. As the chain stretches, at some point it will reach the limit of what the chain tensioner can compensate for. The tensioner uses oil pressure to apply tension to the chain when the car is running. There is also a spring that applies some tensions when the engine is off and there is no oil pressure. What happens is that when the chain is stretched too much, the spring alone cannot apply enough tension, and it becomes possible for the loose chain to jump some teeth on the timing gears. I believe this is why most of the M271 failures occur during engine start up. When the chain skips, major engine damage can occur if the valve timing goes out of sync far enough for the valves to hit the pistons.