Coolant loss / expansion tank (B58)
The low temperature cooling system, expansion tank, and water pump are the typical B58 weak spots. Loss can be slow.
How to check
Inspect the expansion tank seams, ask owner about coolant top-ups.

2023 to 2026SedanM Performance
Photo: Harvey Bold, public domain, via Wikimedia Commons
The G20 M340i post-LCI brings new sharper headlights with the inverted L daytime graphics, a redesigned kidney grille (mesh on the M340i), new bumpers, and inside the move from iDrive 7 to iDrive 8 on the Curved Display, plus a toggle gear selector.
Each part is scored from 0 to 100 on a fixed outside scale. Acclaim comes from published expert lists, launch reviews and awards; the more acclaimed a car, the less its ownership cost counts in this all-time score (its dollars below are unchanged). A part marked not measured carries no weight for this car, and the others share its weight.
8 prices from sources that allow this use (driveway.com), read October 27, 2026: the middle one is $57,523, about 99% of the price new (92% once the price new is put in today's dollars). Asking prices sit above what cars sell for.
Long-term value starts to count in the score once 75% of the 69 generations have permitted prices. Today 43 do.
About $1,986 a year to own ($1,356 to $3,127), about $8,661 over five years, bought at five years old or its own age if older, kept five years.
Expect about $1,400 to $3,100 a year; the bills that decide it are oil filter housing and valve cover gasket leaks, high pressure fuel pump and coolant loss / expansion tank. Ownership risk: low.
Guide Score method v5-final.14, an editorial score built only from permitted, sourced data. How it works.
Colors it came in, most wanted first. Pick one to see the page in it.
2026The best year to buy, reading 66 of 100, about $1,986 a year to own.
No year to think twice about: none reads 3 or more points below the 2026, and no logged fault separates them.
From our log of the changes between model years, each with its source. Only changes the score reads count as reasons; recalls BMW fixes for free, options and tuning notes do not. The cost a year is for a car bought at five years old, or its own age if older, kept five years. How the score works.
The 48V mild hybrid carries over from the 2021 and 2022 cars.
The drivetrain is the pre-LCI car's for 2023 and 2024; the 2025 update brought a revised six with port injection, 386 hp and 398 lb-ft, plus iDrive 8.5.
What goes wrong on this generation, roughly what a fix costs at an independent shop, and how to spot it before you buy. Every M340i generation compared.
Look for oil or coolant residue at the oil filter housing and the valve cover, and ask about coolant top-ups.
Ask about tune history and fueling upgrades, listen for HPFP whine at idle.
Pre-purchase scan for PCV and misfire codes, check idle quality.
NHTSA files some of this car’s recalls and owner complaints under the 3 Series, so they are missing here. Check recalls by VIN, and read complaints by year, make and model, at nhtsa.gov/recalls.
The low temperature cooling system, expansion tank, and water pump are the typical B58 weak spots. Loss can be slow.
Inspect the expansion tank seams, ask owner about coolant top-ups.
The engine-driven high pressure fuel pump and the injectors it feeds can wear, bringing poor running and fuel pressure fault codes. A parts seller says the pumps and injectors on the updated version of this engine, in 2023 and 2024 cars, no longer fail regularly, but that owners will in time replace both; it gives no mileage or rate, no source we read covers the 2025 revision yet, and BMW has issued no bulletin on pump wear.
Ask about tune history and fueling upgrades, listen for HPFP whine at idle.
The plastic oil filter housing and its gaskets can leak oil or coolant, often from about 60,000 miles, and the valve cover gasket can weep. A proposed class action filed in January 2026 covers 2014 to 2021 BMWs with this engine family; BMW has moved to dismiss it, and no class has been certified. Both jobs take many hours of labor.
Look for oil or coolant residue at the oil filter housing and the valve cover, and ask about coolant top-ups.
The crankcase ventilation (PCV) valve's diaphragm in the valve cover can split, as on the earlier B58, whose valve BMW covers for 15 years or 150,000 miles; no BMW bulletin covers this engine version. Signs are rough idle, a whistle at idle and stored codes.
Pre-purchase scan for PCV and misfire codes, check idle quality.
Intake valve carbon deposits build up over time on the direct injection engine and are removed by walnut blasting; one repair shop that sells the service says cleaning is typically needed every 50,000 to 70,000 miles, and BMW schedules no such service. The 2025 update added port injection, which keeps the valves clean.
Ask whether walnut blasting has been done, budget for it on higher mileage cars.
BMW of North America, LLC (BMW) is recalling certain 2023 330i, 330i xDrive, M340i, M340i xDrive, M3, 330e, 330e xDrive, 430i Convertible, 430i xDrive, M440i, 2022-2023 430i, 430i xDrive, M440i xDrive, i4 eDrive40, and i4 M50 vehicles. During a service visit, a replacement electronic control unit (ECU) may have been installed with incorrect programming, which can cause the automatic door locking (ADL) function to not lock the doors as intended.
NHTSA files some of this car’s recalls under the 3 Series, so they are missing here. Check yours by VIN at nhtsa.gov/recalls.
Live from NHTSA, across the 2023 to 2026 model years.
Our estimates at an independent shop, parts and labor; fuel from the EPA.
Pricing tires for this car? Compare the factory sizes at Discount Tire, and ask a local shop to match it.
Fuel from EPA fueleconomy.gov: its yearly cost is for 15,000 miles with 55% city driving, moved here to the miles a year the two-year budget uses. The rest are our estimates at independent-shop and retail prices from September 2026. Service is a year of routine maintenance at 10,000 miles: one or two oil changes, brake fluid, filters, and spark plugs spread over their interval. Repairs are separate. Tires are a mounted set of summer tires; brakes are pads and rotors on both axles. Prices vary by region and shop.
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Set your ZIP and this page shows the asking prices of M340i G20 facelift cars listed for sale within 100 miles of you today, with the cars themselves.
Representative listings, last reviewed September 2026. Examples chosen by us, not a live feed.
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The cars this one gets weighed against, by lineage and by price.
The M Index, once a month: any change to the M340i's guide or score, with the reason, new recalls on M cars, and one thing to check before you buy.