BMW 3 Series Problems

The engine in the car you’re looking at has the codename N42. It has a timing chain rather than a rubber timing belt, so that should not need to be changed for the life of the car. However, life is not always that simple and the N42 has a bit of a reputation for developing wear in the tensioners that keep the timing chain taut. If that happens, you could have a chain loose enough to jump a few teeth on the timing gears and destroy the engine in the process. So a service record and close inspection of the engine is called for before any purchase.

This model BMW was also caught up in the Takata airbag recall debacle. As a result, many BMWs of this era were actually bought back by BMW and scrapped as the cost of fixing the airbag woes was greater than the value of the cars themselves. Make sure any car like this has had the airbags replaced and is not a candidate to be crushed rather than fixed. Quoting the car’s VIN to a BMW dealership should reveal all.

I've used the last versions of both those models for this comparison, which means a 2019 BMW 320d and a 2021 Mercedes-Benz 220d (I'm also assuming you're comparing diesels with diesels).

As such, the BMW holds a slim on-paper advantage with an official combined fuel consumption number of 4.4 litres per 100km, compared with 4.7 litres for the Benz. In the real world, that difference is a very, very small one and means the two vehicles are more or less line-ball for fuel economy.

Real world fuel consumption has a lot more to do with your driving environment and style than it does these laboratory-produced numbers. But the official numbers are valid on the basis that both vehicles were subjected to the same strict test regime, so they do provide a direct comparison, even if you'll almost certainly never match them in real life. Both, however, will surprise you with how frugal they can be.

The 330e is a plug-in hybrid (PHEV), so it has a petrol engine and a smaller battery pack than a full EV (which runs exclusively on battery power). That means the BMW’s battery should be less expensive to replace if it ever needed to be.

At the moment, the world is waiting to find out how long EV batteries last, but it’s looking like between 10 and 20 years is going to be the magic number. A lithium-ion battery like this one will last longer if it’s never over-charged and is cycled regularly rather than left sitting for long periods.

That’s quite low mileage for a 2012 vehicle and, on the surface, suggests that it has led a pretty easy life. but you’d still only buy it if it is presented with a fully-stamped service book to prove that all the critical preventative maintenance has been carried out. These are complex, high performance cars and they won’t tolerate neglect in terms of skipped services.

The major mechanical problems with these cars were found in the engine’s variable valve timing (VANOS) system. Any 'Engine Malfunction' message or 'Check Engine' light in the dashboard could quite easily be caused by a fault in this system. The VANOS arrangement was also the first system to show the effects of poor servicing, so make sure it checks out before you hand over the cash. Fundamentally, though, these cars are not low-maintenance units, so make sure you budget for the necessary ongoing servicing.

Don’t forget, also, that this series of BMW was caught up in the Takata air-bag debacle. So make sure the car has been attended to as part of the global recall and don’t take a chance on any car with no proof of this air-bag replacement being carried out.

There are two likely suspects here. The first is a blown head gasket which is allowing the oil and coolant to mix. Sometimes this shows up as oil in the coolant, sometimes as coolant in the oil. Sometimes both.

But before tearing the engine to pieces to change the gasket, it’s worth checking if the car is fitted with either an engine or transmission oil cooler. These often use the engine’s coolant to keep the oil or transmission fluid cool, and a failed one can allow the two fluids to mix, showing up as oil in the radiator or header tank.