BMW S55: Weak Points, Maintenance, and Reliability Secrets for Owners

Quick Summary

The S55 is BMW M’s twin-turbo inline-six, paired with a seven-speed DCT. Its main weakness is the crank hub, which is held in place by friction alone. Drive it aggressively and the hub can spin, with catastrophic consequences. Regular service every 4,300–6,000 miles and keeping the PCV system in check are the backbone of reliability. This one is for owners and buyers of used M cars.

The Problem

You get in the car, and the idle won’t hold steady. A month later you notice an oil smell, and fresh leaks have shown up under the hood. A familiar picture for BMW S55 owners. The engine is powerful and responsive, but highly stressed—and that means it demands attention. Without proper care, even a legendary engine turns into a source of constant expenses.

Symptoms

• Rough, unstable idle
• Oil leaks on the engine and an oil smell
• Turbo whine under acceleration
• Power loss and rising oil consumption
• Blue smoke from the exhaust
• DCT jerks between shifts, especially when cold
• Clunks over bumps and vague handling

Causes

The crank hub is the S55’s Achilles’ heel. It connects the crankshaft to the camshafts and keeps the valve timing in sync. The design secures the hub by friction alone, so aggressive driving at high rpm can spin it. The consequences: slipped timing, pistons meeting valves, and repair bills that can run all the way to a new cylinder head—or a complete engine.

Oil leaks come from the valve cover gasket and the oil filter housing gasket. Rubber seals lose their elasticity over time. A faulty PCV (crankcase ventilation) system raises pressure inside the crankcase, pushing oil past the seals, and it also makes the engine run rough.

Intercooler pipes endure constant heat and pressure, so the plastic and rubber turn brittle. Internal leaks in the charge air cooling system cut cooling efficiency—air reaches the engine hotter, and the risk of knock grows.

The Fix

Crank Hub

Upgraded hubs with positive mechanical locking—a keyway or gear engagement—eliminate the risk of spinning entirely. Installing one is an investment in peace of mind, especially with a tune or regular track use.

Oil Leaks and PCV

1. Inspect the valve cover gasket and oil filter housing gasket every 25,000–31,000 miles
2. If you find leaks, replace the gaskets
3. Diagnose the PCV system whenever the idle turns rough or oil consumption climbs
4. Check the intercooler pipes for cracks and chafing at every scheduled service

Turbochargers

The S55’s turbos are dependable, but after 62,000–75,000 miles the bearings and seals can wear. The symptoms are whine, power loss, and blue smoke. Catch the problem early—a destroyed turbo sends metal shavings straight into the engine.

DCT Transmission

Change the fluid and filters every 31,000–37,000 miles—more often if you drive hard. Ignore the schedule and the clutch packs and valve body wear out faster.

Suspension

Past 62,000 miles, inspect the front control arm bushings. Worn bushings show up as clunks and vague handling. Secondary signs: uneven tire wear and vibration under braking.

Prevention / Pre-Purchase Checklist

• Ask whether an upgraded crank hub is fitted and whether the car has been tuned—a tuned car without the hub upgrade is at risk
• Inspect the engine for leaks, check the oil level and smell, and make sure there’s no blue smoke
• Exercise the DCT in different modes, especially the shift from first to second gear
• Request the service history from a BMW dealer or a specialist
• Check tire wear and watch for vibration under braking
• Change the oil every 4,300–6,000 miles, using a synthetic that meets BMW specifications
• Warm the engine up before working it hard

The Bottom Line

A well-maintained car with 81,000 miles is more reliable than a neglected low-mileage one. Regular oil changes, proper warm-ups, and on-time DCT and suspension service aren’t expenses—they’re an investment in longevity. Choose a car with a transparent history and don’t skimp on prevention—maintained this way, the S55 will last for years and keep delivering its performance.