Which BMW Inline-6 Is More Reliable, B58 Or M54?

In an age when most car companies have shifted toward building the more compact V6 or a turbocharged inline-4, BMW has kept a candle on for the venerable inline-6, the best six-cylinder engine. In constant production at the Bavarian manufacturer since the 1930s, the straight-6 allows for greater balance and fewer parts than a V-engine. It provides for smooth power delivery and can handle a range of uses, from off-roaders to performance hounds.

One of BMW's more popular offerings in this layout was the M54 (in production from 2000 to 2006). While BMW engines are generally considered pretty solid, the M54 was stood out for its great balance of power and efficiency when stock, and it was extremely modder-friendly to boot. Even better for long-term owners, it has developed a fantastic reputation for reliability, too. So while it's not as advanced or powerful as its modern offshoot, the B58, might it be a better choice?

Fortunately, the B58 has also proven to be a dependable piece of machinery over the long haul, and across its 10-year (and counting) lifespan, it does not appear to have developed any major problems. So in terms of reliability, which of these two engines you have matters less than making sure you bring it in for maintenance regularly.

In 2000, BMW didn't just wave goodbye the last millennium, but also to the cast-iron blocks of its earlier engines. The M54 engine of that era upgraded to an aluminum block, which was far lighter, increasing both fuel efficiency and performance. As a naturally aspirated engine, it didn't have to worry about turbo lag, so putting your foot down meant instant joy. At standard spec, it could make up to 235 horsepower and 222 pound-feet of torque.

It was also famously reliable, making for a much-loved engine that was both quick and resilient. Still, the M54 was known to see issues with the oil filter housing gasket and overheating generally. It also used BMW's VANOS, a variable valve timing system. Given its complexity, it's not a surprise that it can be a relatively common point of failure. None of these issues were all that frequent, however.

The B58 is a 3.0-liter inline-6 featuring an aluminum block with a closed-deck design, making for a very lightweight engine that's still strong enough for a truly impressive compression ratio of 11.0:1. It's only got one turbocharger, but it is twin-scroll, meaning that it keeps its power better as you go on and off the accelerator. All that can add up to 382 hp at standard spec, though given the strength and resilience of the engine overall, tuners can take that up much, much higher.

While its reputation is that it's dependable, it does see a few issues now and again. The B58 sometimes has coolant levels drop suddenly in the primary reservoir, which in turn leads to overheating. Perhaps not as a coincidence, some other common issues involve the valve cover and cylinder head gaskets failing, in both cases caused by overheating. Additionally, the modern B58 version of the VANOS variable valve timing system is more advanced and slightly harder to repair than the older M54 version, but this really shouldn't be a dealbreaker if you're thinking about the newer engine.