BMW M Performance Buying Guide: What to Check on the M340i, M240i and the 40i Range
BMW’s “M Performance” cars (the 35i and 40i models like the M135i, M240i and M340i) sit between the standard range and the full M cars. They deliver most of the pace for less money, with lower running costs, and they’ve become some of the best all-round performance buys around. They’re also frequently modified and, increasingly, misunderstood at point of sale.
The single most important thing to understand before buying one: a car’s history is not the same as its condition, and neither is fully visible in the car advert. There are also two naming traps that matter for value: an M340i is not an M3, and the “35i” badge has covered two completely different engines. This guide explains the range, what tends to need checking, and what a car advert won’t tell you.
At a glance: the engines behind the badges
| Badge | Examples | Years | Engine | Drive |
|---|---|---|---|---|
| 35i (early) | F20 M135i, F22 M235i | 2012–2016 | 3.0 single-turbo six (N55) | RWD |
| 35i (modern) | F40 M135i, F44 M235i, X2 M35i | 2019–present | 2.0 turbo four (B48) | FWD / xDrive |
| 40i | M140i, M240i (RWD); M340i, M440i, X3/X4 M40i, Z4 M40i (xDrive) | 2016–present | 3.0 single-turbo six (B58) | RWD / xDrive |
Two things stand out. The “35i” badge changed engine entirely: the early M135i/M235i were rear-drive N55 straight-sixes; the modern ones are front-drive-based B48 fours, very different cars, so be sure which one a car advert is. And the 40i cars use the single-turbo B58 six, one of BMW’s most respected modern engines (40i cars from late 2020 added a 48V mild-hybrid system). Note that the M550i and X5 M50i are a different animal, twin-turbo N63 V8s, and aren’t covered here.
Common problems by engine
Early 35i: the N55 six
The early M135i/M235i share the N55 with the first BMW M2, so the same checks apply: the plastic charge pipe can split, the oil filter housing gasket can leak, the plastic valve cover/PCV can crack, and the electric water pump can fail with little warning. See the M2 guide for more on the N55.
40i: the B58 six
- Heat-management module / coolant. The B58’s main known weakness is around the heat-management module: a plastic coolant connector can degrade and crack, causing a slow, hidden coolant leak, a tell-tale is a sweet, “burnt-sugar” smell under the bonnet without an obvious puddle. Check for it.
- PCV in the valve cover. The PCV diaphragm is built into the plastic valve cover and can split over time: symptoms include a squeal at idle, blue smoke and oil-fouled plugs; the fix is the whole valve cover.
- Early oil pump. Some early (Gen-1, roughly 2016–2018) cars have been reported to suffer oil-pump issues: worth checking the service history and any oil-pressure warnings on an early car.
Modern 35i: the B48 four
- Coolant vent pipe. A brittle plastic vent pipe between the expansion tank and the cylinder head can snap (even during routine servicing), dumping coolant: check it’s intact and there’s no overheating history.
- Oil filter housing gasket. As on other BMWs, this composite seal can leak; on the B48 the oil can drip onto the alternator and cause charging faults: check for leaks at the front of the engine.
All: modification and “is it really standard?”
These tune readily and many have been mapped: establish what’s been done. Because they’re cheaper than full M cars, they’re often modified to chase M-car pace, so a clear, evidenced account matters. Confirm the infotainment, cameras and driver-assist features work on the test drive.
Beyond the mechanicals: history and provenance red flags
Two cars with identical engines can be worth thousands apart on history alone. Before you focus on mechanical condition, the paper trail has to stand up:
- Service history gaps: especially around major-service intervals. Missing stamps aren’t automatically disqualifying, but they change the price.
- Mileage that doesn’t add up: MOT records should tell a consistent story year-on-year. A jump or a stall is worth understanding before you view.
- Outstanding finance: a car can’t be sold cleanly with money owed against it. This is a five-minute check that prevents a very bad day.
- Accident or write-off markers: a recorded repair isn’t always a deal-breaker, but you need to know it’s there and price accordingly.
- Specification that doesn’t match the car advert: claimed options that aren’t actually fitted are common, and the exact model badge matters (a 40i is not an M car; an early 35i is not a modern one).
None of these require you to be in the same room as the car. All of them are checkable in advance.
What a car advert and a test drive won’t tell you
It helps to think of the purchase as three layers of truth:
- What the seller says: the car advert, the description, the conversation. Useful, but unverified.
- What the records say: MOT and mileage consistency, finance, stolen and write-off markers. This is data verification, and it can be done before you travel.
- What only a physical inspection reveals: compression and leak-down results, suspension and bushing wear, transmission and driveline health, the things you can only find with the car on a ramp.
Most buyers do layer 1, skip straight to a test drive, and only reach layer 3 (a proper PPI) on the one car they’ve already half-committed to: sometimes after a long drive to see it. Doing layer 2 first is what stops you wasting a Saturday on a car whose history was never going to check out.
To be clear about the limits: data verification confirms a car is what it claims to be on paper. It does not replace a physical, mechanical pre-purchase inspection. The two do different jobs, and a careful buyer does both: in that order.
How Chequered Past helps
Chequered Past is the layer-2 step. You give us the registration; we check the official records on that car: the factory spec, MOT and mileage consistency, outstanding finance, stolen and write-off markers, keepers and the value, and we’re explicit about anything we couldn’t confirm.
What it does: tells you, before you travel, whether a car is what it says it is. What it doesn’t do: replace a physical inspection of mechanical condition. We’ll always tell you where that line is.
Run a history check on an M Performance car you’re considering →
Frequently asked questions
Is an M340i the same as an M3? No. The M340i is an M Performance car with a single-turbo B58 six; the M3 is a full M car with a twin-turbo S-series engine and far more focused hardware. The M340i is superb value, but it’s a different (and cheaper) car: make sure you’re paying M Performance money, not M money.
Why do two M135is have completely different engines? Because the badge spanned two generations on different engines: the early (2012–2016) M135i is a rear-drive N55 straight-six, while the modern (2019-on) M135i is a front-drive-based B48 four-cylinder. They drive very differently: be sure which one you’re looking at.
Do I need the car’s registration? Yes. The free check and the £10 vehicle history check both run on the registration.
Can you check a modified M Performance car? Yes. We surface the signals; you decide what they mean for you. The goal is an informed decision, not a pass/fail.
Other BMW M guides: BMW M buying guide hub
Chequered Past is an independent analysis service and is not affiliated with, endorsed by, or connected to BMW AG or any vehicle manufacturer. Data is drawn from licensed DVLA and DVSA records via our data provider.