The most reliable BMW Engine of the last 20 years

Of all the car manufacturers out there, few have a stigma attached to them in regards to reliability quite like BMW. The Bavarian marque is often associated with catastrophic failures, astronomical repair costs and empty bank accounts, with owners left sobbing into their invoice for a laundry list of expensive repairs. While this is indeed sometimes the case, to let this somewhat unfair misconseption cast a shadow over all of the brand's products would be an unfortunate mistake. You see, although there are a handful of BMW engines out there that are better suited to automotive masochists than those who want dependable transportation, there are also some absolute gems that are genuinely more reliable than what you'll find under the bonnet of a Toyota.

The N52 six-cylinder is a perfect example, and gets our vote as the most reliable engine you'll find in any modern BMW. Produced from 2004 all the way through to 2015, the N52 was the last naturally-aspirated engine that BMW built before completing their transition to turbocharging across their entire lineup, and marked the end of nearly a century of NA inline-six production since BMW's first ever engine back in 1917. Available in both 2.5 and 3 litre configurations, there were numerous variants of the N52 such as the N51 SULEV (Super ultra-low emissions vehicle) that was sold in parts of the United States with stricter emissions requirements, and the updated N53 which introduced direct-injection and ditched Valvetronic (variable valve lift) but was not sold in the US, Malaysian or Australian markets due to high sulphur content in these countires fuels. However, of these variants the N52 has proven the most reliable, hence why it stayed in production for the longest period.

BMW N52 inline-six (Picture: BMW)

BMW N52 inline-six (Picture: BMW)

Inline-sixes are BMW's bread and butter in the same way V12's are for Ferrari, and for this reason they tend to be the most well-sorted. While BMW's four and eight cylinder engines, especially in older models, are often plagued by issues, the sixes rarely experience any serious problems that will financially scar you. What makes the N52 more reliable than other six-cylinder BMW motors though? Right off the bat, being the last naturally-aspirated inline-six sold by the company it is inherently less complex than the turbocharged units that replaced it and therefore has less components that could potentially fail. Although the latest turbocharged BMW engines seem to be fairly relaible (for now, at least) early attempts such as the N54 demonstrated that the jump to forced induction was going to take BMW's engineers some time to completely sort out.

So what about the older engines then, surely they are less complex still, right? Correct, however as they age their tendancy to have issues increases. The N52's predecessor, the M54, is a brilliant engine and some would likely argue it is more deserving of the 'most reliable' accolade. However as they grow older and clock up higher mileage things like worn out piston rings, loss of compression and others problmes commonly associated with ageing engines are of greater concern. The N52 is at an age where cars to which it is fitted have depreciated to very affordable prices, yet they are still relatively modern and have a significant amount of life remaining, especially if you get a more recent one. Having said this, the lifespan of the N52 is quite long and it is not uncommon to find examples out there with over 300,000 miles (or nearly 500,000 kilometers) that are still running flawlessly. These engines are workhorses and can take a beating, they're in the car you take out to run errands while your V8 or 4 pot BMW is at the mechanic getting fixed.

BMW inline-six engines (Picture: Wikimedia Commons)

BMW inline-six engines (Picture: Wikimedia Commons)

Obviously, even the best engines aren't perfect and still have certain areas that may need attention at some point, so what problems can you expect to encounter during N52 ownership? There is only one issue which is likely to actually require you to pull over, that being the water pump. Unlike most engines which use a mechanical water pump, the N52 uses an electric one. The benefit of this is it can communicate with the ECU which adjusts flow rate depending on driving style to offer better cooling capability when you need it, yet better fuel efficiency while cruising. Unfortunately these factory water pumps were somewhat poorly built and tended to fail around 80,000 miles (130,000 kilometers). The good news is that many replacment units are built to a higher quality and will last substantially longer, making it a one time job for most engines.

The most common failure of all on the N52 (and one I've experianced myself) is the VANOS solenoids. These control the flow of oil to the actuators which move both camshafts thus altering the valve timing. When they cease to function correctly the car will still function, however it will be down on power and may idle poorly and experiance other rough running characteristics. Thankfully they are very easily accessible and only take around 5-10 minitues to replace. While they can be found very cheaply online, you're best off spending a little more for genuine BMW units as cheaper ones often cannot perform as the ECU asks of them and will leave the engine down on power. Many people think cleaning the solenoids is a solution however this generally has no result, or only offers a temporary fix.

BMW E90 330i (Picture: BMW)

BMW E90 330i (Picture: BMW)

Other than these two things and the usual gasket oil-leaks you'll find on all ageing European cars, the N52 is a bulletproof motor that offers a delightful driving experiance to boot. Buttery smooth and with swathes of low down torque available, it is one of the great BMW inline-sixes and deserves a place in the Bavarian engine building hall of fame, if such a thing existed. So if you're new to the world of BMW and are looking for a car that will be dependable, or perhaps have had bad experiances in the past with other BMW's, N52 powered models are a fantastic choice and our recommendation to those who want the most trouble-free ownership experience possible.