BMW M240i Convertible F23

The most common B58 issue, now subject to a class-action lawsuit in the US (filed January 2026). The plastic coolant vent hose that connects the oil filter housing module to the expansion tank becomes brittle from thermal cycling, typically between 80,000 and 130,000 km. The oil filter housing gasket itself degrades simultaneously. Symptoms include a sweet coolant smell after driving, slowly declining coolant level, and white crystalline residue near the housing. A proper repair requires replacing the full OFHG gasket set, the plastic vent hose, and the single-use aluminum bolts simultaneously. Replacing only the gasket without the hose often results in a return leak. At an independent specialist, expect €600-900; BMW dealers charge €1,000-1,500. Upgrading the plastic coolant connector to an aftermarket aluminum version is recommended as a permanent fix. If ignored, low coolant can lead to overheating and serious engine damage.

The F23 convertible roof motor sits in the boot area where it is exposed to water ingress. Over time, moisture damages the motor windings, Hall sensors, and position switches, causing the roof to stop mid-cycle, fail to latch properly, or refuse to operate entirely. This is a well-documented F23 issue that specialist convertible repair shops frequently encounter. The OEM roof motor alone costs approximately €1,400 from BMW, with additional fitting costs. Including labor, a full motor replacement runs €1,800-2,500 at a BMW dealer. Specialist convertible repair shops may offer motor rebuilds for €1,200-1,500. Regular inspection of the boot area for moisture, ensuring drain channels are clear, and addressing any water pooling early can help prevent motor damage.

The B58 integrates the positive crankcase ventilation system into the valve cover rather than as a separate component. The rubber PCV diaphragm can tear or rupture, typically after 80,000-130,000 km, causing blue or white exhaust smoke, increased oil consumption, rough idle, and potentially a high-frequency whistling noise from the valve cover area. BMW issued a warranty extension (SIB 01 14 23) covering the PCV valve cover for 15 years or 240,000 km from the original registration date, so many M240i examples may still be covered. If out of warranty, aftermarket PCV diaphragm repair kits cost €50-150 and can be installed without removing the valve cover, avoiding the need for full replacement. Full OEM valve cover replacement at a dealer costs €800-1,200 including labor.

The B58 comes with a factory plastic charge pipe routing compressed air from the intercooler to the intake manifold. Over time, heat cycling causes the plastic to become brittle, and the pipe can crack or blow off entirely, resulting in an immediate loss of boost pressure and limp mode. This can happen on completely stock cars, though it is more common on tuned examples with increased boost. On stock M240i models, it typically occurs after 80,000-130,000 km. The OEM plastic replacement costs approximately €80-120, but most specialists recommend upgrading to an aluminium aftermarket charge pipe (€150-250 installed) that eliminates the issue permanently. This is widely considered preventive maintenance on B58-powered BMWs.

The B58 uses an electric water pump with a plastic/composite impeller that can crack or deform under thermal stress. Failure is abrupt and the engine can overheat within minutes, unlike a mechanical pump that typically leaks or whines before failing. Most failures occur between 120,000 and 160,000 km, though some earlier failures around 80,000 km are documented. The thermostat is usually replaced at the same time as a preventive measure. OEM pump and thermostat together cost approximately €400-500 in parts. With 3-4 hours of labor, total repair runs €600-900 at an independent specialist, or €900-1,200 at a BMW dealer. Preventive replacement around 120,000 km is recommended.

The VANOS solenoid O-rings are a common wear point on the B58. As the rubber O-rings age and harden from heat exposure, they allow oil to seep past, disrupting the solenoid's ability to actuate properly. This triggers VANOS fault codes, rough idle, and reduced throttle response. Typically occurs after 80,000-100,000 km. The solenoids themselves cost approximately €80-100 each, and replacement takes about 30-60 minutes. Total professional repair cost is €200-500 depending on whether one or both solenoids need attention. Many owners report this as a straightforward DIY fix. Regular oil changes with quality BMW LL-01 approved synthetic oil help keep solenoids free of sludge and delay this issue.

The F23 convertible can develop water leaks into the boot area over time as the roof seals age and drain channels become blocked with debris. Water accumulates in the boot floor, potentially damaging the audio amplifier, wiring harnesses, and the roof motor itself. Symptoms include a damp or musty smell from the boot, wet carpet, or visible water pooling. Seal replacement costs €300-500 depending on which seals are affected. If the water has damaged electronic components such as the amplifier or control modules, costs can reach €800-1,000. Regular inspection and cleaning of the drain channels, and ensuring seals remain supple with rubber conditioner, significantly reduces this risk. Cars that have been parked outdoors long-term in wet climates are most affected.