Which BMW 4 Series Is the Most Reliable? Full Engine Comparison
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The BMW 4 Series has been around since 2013, when BMW split the 3 Series coupe into its own line. Two generations later, the F32 (2013–2020) and the G22 (2020 onwards), there is now a reasonable spread of used examples on the UK market at various price points. Which one to buy comes down, more than almost anything else, to which engine is under the bonnet. Here is an honest comparison of every significant engine option across both generations.
F32 BMW 4 Series (2013–2020) — Engine by Engine
N20 — the one to avoid
The N20 2.0-litre petrol went into the early F32 420i and 428i. It is not a terrible engine, but it has a known timing chain problem that has affected enough owners to give it a poor reputation in the BMW community. The chain and its plastic guides can wear and crack, particularly on cars that have been run on extended oil change intervals. The symptoms, a rattle at cold start that clears after a few seconds, are easy to miss until the damage is already done.
A chain replacement on the N20 is not cheap. If you are looking at an early F32 420i or 428i, check specifically for this history. Without it, and without a clean bill of health from a specialist inspection, the N20 is a risk worth pricing in.
B48 — the sensible choice
From around 2016, BMW replaced the N20 with the B48 in 420i and 430i variants. The B48 is a meaningfully better engine. BMW redesigned the timing chain system, moved to a closed-deck block construction shared with the B58 six-cylinder, and addressed most of what the N20 got wrong. It is generally considered one of the more dependable modern turbocharged four-cylinders available in the used market.
The main things to watch on a B48 are oil leaks from the valve cover and oil filter housing gaskets, both common on higher-mileage examples, and carbon buildup on the intake valves, which is standard for any direct injection engine. Neither is a reason to avoid the car, but both should be checked on any B48 over 60,000 miles.
N55 — smooth and capable
The N55 3.0-litre straight-six went into the F32 435i and early M4 variants. It is a well-liked engine with a strong reliability record when maintained correctly. The main known faults are oil leaks from the valve cover and oil filter housing gaskets, same as the B48, and charge pipe cracking under sustained boost, which is a relatively common and inexpensive fix. Oil changes every 6,000 to 8,000 miles keep the N55 in good shape for a long time.
N57 — the diesel pick
The N57 diesel went into the F32 420d and 430d. Unlike the earlier N47 diesel that plagued the previous generation of BMW diesels with rear-mounted timing chain failures, the N57 has a front-mounted chain, a significant improvement in terms of both accessibility and cost of maintenance. Turbocharger wear is the main concern on higher-mileage N57 cars, particularly twin-turbo variants. A pre-purchase boost pressure check is worthwhile on any N57 over 80,000 miles.
B58 — the best of the F32 range
The B58 3.0-litre straight-six appeared in the M440i and some late F32 440i variants. It is widely regarded as one of BMW's best modern engines, a closed-deck block, front-mounted chain, strong reliability record, and enough power to make the 4 Series properly quick. If you can find an F32 440i or M440i with the B58, you are getting the most capable and dependable engine in the F32 range.
Confirm which engine is in any F32 you are considering using the full engine code on the block or via RealOEM.com with your VIN. The model badge alone, 420i, 430i, 440i, does not tell you whether you have the older N-series engine or the newer B-series replacement.
G22 BMW 4 Series (2020 Onwards) — A Simpler Picture
The G22 arrived with a cleaner engine lineup. All petrol variants use either the B48 four-cylinder or the B58 six-cylinder, both of which are B-series engines with the reliability improvements that came with that generation.
B48 — 420i and 430i
The G22 420i and 430i use the B48 throughout the generation. Same engine as the later F32 variants, in a slightly more refined state of tune. The same maintenance points apply: valve cover leaks, oil filter housing, intake valve carbon buildup at higher mileage. All manageable.
B58 — M440i and 440i
The G22 440i and M440i use the B58 in M Performance tune, producing 374hp (or 386hp on the LCI). This is the engine most enthusiasts would choose in the 4 Series range, and for good reason. It is smooth, powerful, genuinely reliable with regular oil changes, and has enough headroom to feel effortless in everyday driving.
The Verdict
For the F32: avoid early N20-engined cars unless chain history is documented. The B48 is a solid choice from 2016 onwards, the N55 is well-regarded with the right service history, and the B58 is the pick of the range. The N57 diesel is fine if the turbocharger.
For the G22: both available engines are dependable. The B48 is competent and economical. The B58 in M440i form is the best all-round 4 Series you can buy, and if you need BMW spares for either engine, the used genuine parts market for G-generation BMWs is now well-stocked and accessible.
If you are buying a used F32, always confirm the engine code, not just the badge. A 420i built before 2016 has the N20. A 420i built from 2016 has the B48. They are different engines with different reliability profiles.
If you own a BMW 4 Series and need BMW engine parts, gearbox components, suspension, or anything else, MT Auto Parts is worth a look before you head to a dealer. We are a BMW breakers yard in Thurnscoe, South Yorkshire, and we break F, G, and U generation models daily. That means B48 engines, B58 engines, N55 units, N57 diesels, and the parts that come off them, all with the donor car's mileage documented and a 30-day warranty (T&C apply). We have been doing this since 2020 and have over 15,000 five-star reviews from BMW owners and garages across the UK. Most parts go out the next day. If you are not sure what you need or want to check fitment before ordering, send your registration on WhatsApp, and we will sort it from there. mtautoparts.com.
Disclaimer: This article is provided for general information only and does not constitute professional mechanical or legal advice. Reliability assessments are based on widely reported owner and workshop experience and may not reflect every individual case. Always have a used vehicle inspected by a qualified BMW specialist before purchase. MT Auto Parts accepts no liability for decisions made based on information in this article.
