BMW F30 340i & the B58: The One to Have
If you ask which F30 to buy, the enthusiast answer is almost always the same: the 340i. It arrived with the 2015 LCI facelift and brought the B58 — a 3.0-litre single-turbo straight-six that's become one of BMW's most respected modern engines. Here's why it earns that reputation, and the short list of things to still keep an eye on.
The short version
- The 340i (2016+) replaced the 335i and swapped the N55 for the B58.
- The B58 is widely regarded as one of BMW's most reliable and tuneable modern engines.
- Few real faults — mostly the usual water pump, oil filter housing gasket and valve cover gasket over time.
- Huge tuning headroom: big, safe gains on a simple tune, with strong internals.
- If buying an F30 and budget allows, the 340i is the connoisseur's pick — buy on history all the same.
The B58 (full code B58B30) debuted in the 340i and went on to power the Supra, the M340i, the Toyota GR Supra and more — a sign of how much faith BMW and partners placed in it. In the F30 it makes around 320–326 hp and turns the 340i into a properly quick, smooth, effortless car. Mechanically it's a generational step on from the N55: a closed-deck block, a more integrated cooling and thermal-management system, and a reputation for taking abuse and big power with ease.
Why It's the One to Have
Strength, smoothness and tuning headroom.
Three things put the B58 at the top of the F30 range. First, durability — the bottom end is famously strong, and the engine routinely shrugs off high mileage and tuning. Second, refinement — it's smoother and more eager than the N55, with a broad, flexible torque curve. Third, tuning — a simple ECU flash unlocks large, dependable power gains while the stock internals hold up, which is exactly why it has such a following. For most buyers, the 340i is the F30 that best balances pace, polish and peace of mind.
What Little There Is to Watch
The B58's weak points are minor — and mostly age-related.
Water Pump & Thermostat Wear item
As with every modern BMW six, the electric water pump and thermostat are wear items that can fail over the years. It's the single most likely thing to need attention on a higher-mileage B58. Not a design flaw — just maintenance to budget for, often replaced as a pair.
Watch for: overheating warning, limp mode, temperature swings, "drivetrain malfunction" message.
Oil Filter Housing & Valve Cover Gaskets Seeps with age
Like its predecessors, the B58 can develop minor oil weeping from the oil filter housing gasket and valve cover gasket as the seals age. It's slow, cheap to address, and best caught before oil reaches the belt. Routine, not alarming.
Watch for: faint oil smell when warm, light residue around the filter housing or valve cover.
Carbon Build-Up Slow, DI trait
The B58 is direct-injected, so intake-valve carbon accumulates over time as on any DI engine — but it tends to build more slowly here, and many cars go a long way before it matters. Eventually a walnut blast cleans it up. Maintenance, not a fault.
Watch for: slight rough running or lost crispness only at high mileage.
Charge Pipe (Tuned Cars) If modified
Stock, this isn't really a concern. On heavily tuned B58s running a lot of boost, the factory charge pipe and a few plastic cooling components can become weak links — common upgrade territory for high-power builds, but a non-issue on a standard 340i.
Watch for: boost-related faults only on cars making significantly more than stock power.
340i vs 335i — Which F30 Six?
Both are great; the B58 is the newer, stronger engine.
| 335i (N55) | 340i (B58) | |
|---|---|---|
| Years | 2012–2015 (pre-LCI) | 2016–2019 (LCI) |
| Engine | N55 single-turbo six | B58 single-turbo six |
| Reliability | Good | Excellent |
| Refinement | Strong | Smoother, more eager |
| Tuning headroom | Good | Exceptional |
| Quirks | Wastegate rattle, VANOS | Few — mostly wear items |
Both are excellent turbo-six 3 Series. The 335i is the value play and still a lovely car; the 340i is the newer, stronger, more tuneable engine and the one most enthusiasts would stretch for if the budget's there.
FAQ
Is the BMW B58 really that reliable?
Yes — it's widely regarded as one of BMW's most dependable modern engines, with a strong bottom end and a reputation for handling high mileage and tuning well. It's not maintenance-free (water pump, gaskets age like any engine), but as engines go it's about as trustworthy as modern turbo BMWs get.
Is the 340i better than the 335i?
For most buyers, yes. The 340i's B58 is newer, smoother, stronger and more tuneable than the 335i's N55, with fewer quirks. The 335i is the value choice and still very good, but if the budget allows, the 340i is the connoisseur's pick.
What goes wrong with the B58 in the F30 340i?
Very little by modern standards. The main items are age-related: the electric water pump/thermostat, and minor oil weeping from the filter housing and valve cover gaskets. Carbon build-up comes eventually but slowly. None of it is a design flaw.
Can you tune a 340i?
Absolutely — it's one of the B58's biggest draws. A simple ECU flash delivers large, dependable power gains while the stock internals cope well. Just keep an eye on supporting parts (like the charge pipe) on higher-power builds, and tune responsibly.
Which years are the F30 340i?
The 340i arrived with the 2015 LCI facelift and ran through to the end of F30 production around 2018–2019, when the G20 took over. It replaced the pre-LCI 335i.
The Bottom Line
The F30 340i is the easy enthusiast recommendation: the B58 is strong, smooth, gloriously tuneable and about as reliable as modern turbo BMWs get. The only real "problems" are ordinary wear items — water pump, gaskets — plus eventual carbon build-up. Buy the best-maintained one you can, look after the cooling system, and it'll be a superb car for years. More on the F30 hub, the 335i comparison, and the buyer's guide.