BMW S65 Engine Explained: Reliability, Tuning, and Efficiency

The BMW S65B40 is a 4.0-liter naturally aspirated V8 that powered the E92 M3, E90 M3 (sedan), and E93 M3 (convertible) from 2007 to 2013. This high-revving V8 was a major departure from its predecessor, the S54 inline-six, and drew direct inspiration from BMW’s S85 V10 found in the E60 M5. It’s also one of the most exciting engines BMW has ever made, and the iconic M3 only used the V8s once.

Designed as a lightweight, high-performance engine, the S65 features individual throttle bodies, an 8,400 RPM redline, and a motorsport-inspired design. While it delivered raw power and an exhilarating driving experience, it also developed a reputation for specific reliability concerns. In this article, we will break down the S65’s engineering, reliability issues, tuning potential, and fuel efficiency.

The S65 features an oversquare bore and stroke, allowing it to rev freely while maintaining a strong power curve. The dry-sump lubrication system found in BMW’s V10 S85 was omitted for cost reasons, but the S65 still had a sophisticated quasi-dry sump oiling system for improved high-G cornering capability.

BMW S65 Engine Versions

S65B40

• Displacement: 3,999 cc (244.0 cu in)
• Power Output: 309 kW (420 PS; 414 hp) @ 8,300 rpm
• Torque: 400 N⋅m (295 lb⋅ft) @ 3,900 rpm
• Years Produced: 2007-2013
• Bore & Stroke: 92 mm (3.6 in) x 75.2 mm (3.0 in)

Applications:

• 2008-2013 BMW E90/E92/E93 M3
  2009-2014 Wiesmann MF4-S

S65B44

• Displacement: 4,361 cc (266.1 cu in)
• Power Output: 331 kW (450 PS; 444 hp) @ 8,300 rpm
• Torque: 440 N⋅m (325 lb⋅ft) @ 3,750 rpm
• Years Produced: 2010-2012
• Bore & Stroke: 92 mm (3.6 in) x 82 mm (3.23 in)
• Features: Enlarged stroke for increased displacement and Lightweight titanium exhaust system

Applications:

• 2010-2011 BMW E92 M3 GTS
• 2011-2012 BMW E90 M3 CRT sedan

Reliability: Common Issues & Fixes

The S65 V8 is one of BMW’s most highly revered engines—but it’s also notorious for maintenance costs and a few key reliability concerns. While it’s a strong and well-engineered naturally aspirated V8, it does have its fair share of weak points that can lead to expensive repairs if not addressed in time. Let’s break down the most common S65 issues, their causes, and how to prevent them.

1. Rod Bearing Wear (The Biggest Issue)

• Problem: The factory rod bearings are a well-known weak point, often showing premature wear due to tight clearances and inadequate lubrication.
• Symptoms: Metal shavings in oil, knocking sounds, or catastrophic failure in extreme cases.
• Solution: Rod bearing replacement is strongly recommended around 60,000–80,000 miles (100,000–130,000 km). Many owners opt for BE Bearings or VAC Motorsport bearings with better clearance and coated materials to prevent premature wear.

2. Throttle Actuator Failure

• Problem: The electronic throttle actuators wear out due to internal gear failure or PCB degradation, often triggering limp mode and error codes (2B15, 2B16, 2B21).
• Solution: Rebuild or replace throttle actuators. Rebuilt units from Rebuild UK or Lifetime Warranty Actuators offer a more permanent fix than OEM replacements.

3. Idle Control Valve (ICV) Failure

• Problem: Idle issues, rough running, or fault codes related to air control.
• Solution: Cleaning the ICV may help, but in some cases, replacement is required.

4. VANOS System Issues

• Problem: The VANOS solenoids can fail over time, leading to power loss, rough idle, and error codes.
• Solution: Cleaning or replacing the VANOS solenoids can help, and upgrading to newer versions can improve reliability.

5. Cooling System Weak Points

• Problem: The water pump and thermostat can fail over time, leading to overheating.
• Solution: Proactively replace the water pump every 60,000–80,000 miles to prevent overheating issues.

6. Carbon Buildup on Intake Valves

• Problem: Unlike direct injection engines, the S65 is port-injected, meaning it doesn’t suffer from severe carbon buildup. However, high-mileage engines may develop some deposits.
• Solution: A manual intake cleaning is rarely needed but can be beneficial.

7. Clutch & Flywheel Wear (Especially With DCT Cars)

• Problem: The OEM clutch and flywheel wear down quickly, especially if driven aggressively.
• Symptoms: Slipping clutch (in manual cars), harsh shifting (in DCT cars), unusual noises during engagement

Why Does the E9X M3 Have a Poor Reliability Reputation?

The E9X M3 itself is not inherently unreliable, but its high-maintenance costs and engine-specific issues make it less appealing to the average owner. When compared to other high-performance cars, it’s more reliable than an E60 M5 (S85 V10) or an N54-powered BMW, but it still requires preventative maintenance and a proper budget.

Tuning Potential: How Much Power Can the S65 Handle?

The S65 is already highly optimized from the factory, but some NA tuning and forced induction options exist.

1. Naturally Aspirated Mods

Since the S65 is already high-strung, NA tuning yields modest but noticeable gains.

Tune & Exhaust Mods:

• ECU Tune (ESS, BPM, Evolve, VF Engineering) → +20-30 hp
• Test Pipes or High-Flow Cats → +10-20 hp
• Full Exhaust (Akrapovič, Eisenmann, Supersprint, etc.) → +15-25 hp
• Carbon Intake (Eventuri, Macht Schnell, Dinan, CSL-style box) → +10-20 hp
• Ported Heads & Cams → +40-50 hp (high-cost, race-level mod)
• Final NA Output: 450-480 hp

2. Supercharging

• ESS VT2-625 Kit (~6-7 psi boost) → 600 hp
• Gintani or VF Engineering Supercharger → 550-650 hp
• Built Engine & High-Boost Kit (~12 psi) → 700+ hp

All these mods might be pushing beyond the capability of the engine so caution is recommended.

3. Drivetrain Mods

Because the S65 loves revs, shorter final drive ratios (4.10 or 4.30) make a huge difference in acceleration.

Fuel Efficiency

The BMW S65 V8 is notorious for poor fuel efficiency, which is expected given its high-revving nature and motorsport-derived design. With an official rating of around 14-16 MPG combined, real-world figures often dip even lower, especially during spirited driving. In the city, the S65 typically manages 12-14 MPG, while highway driving under light throttle can yield 18-21 MPG at best. The lack of modern cylinder deactivation or turbocharging means the engine constantly consumes fuel, even at low loads. Owners who track their cars or drive aggressively will see even worse numbers, sometimes below 10 MPG. While fuel costs are a downside, most enthusiasts consider it a fair trade-off for the glorious naturally aspirated V8 experience that the S65 delivers.

Is the BMW S65 a Good Engine?

The BMW S65 V8 is an engineering masterpiece—a naturally aspirated, high-revving, motorsport-inspired engine that delivers an unforgettable driving experience. However, it comes with notable maintenance requirements, and rod bearings and throttle actuators are must-fix items.