BMW S63 V8 Reliability: The Definitive Guide (S63, S63TU, S63TU4)
Common Failure Points & Costs
| Component | Failure Mileage | Symptom | Est. Cost (USD) | Risk Level |
|---|---|---|---|---|
| Rod Bearings (S63TU) | 60k - 80k miles | Knocking noise, copper in oil, catastrophic seizure | $2,500 - $3,500 (Preventive) / $15,000+ (Engine Replacement) | Critical |
| Fuel Injectors (Piezo) | 40k - 60k miles | Misfires, fuel smell, oil dilution (cylinder washing) | $2,500 - $4,000 (Set of 8) | Critical |
| Turbo Coolant Lines | 50k - 80k miles | Coolant smell, leaking at turbo fittings, rubber decay | $1,500 - $2,500 | High |
| Crank Hub Slip (S63TU) | Random (High Load/Tuned) | Timing error, limp mode, valve-to-piston contact | $3,500 - $5,000 (Pinned Hub Fix) | High |
| Ignition Coils | 30k - 50k miles | Misfires under load, drivetrain malfunction | $400 - $800 | Medium |
| Oil Consumption | All Mileages | Low oil warning every 1,000 miles | $15/quart (Normal Operation) | Medium |
| PCV System (CCV) | 60k - 90k miles | Whistling noise, high oil consumption, rear main seal squeal | $800 - $1,500 | Medium |
| Vanos Solenoids | 70k - 100k miles | Rough idle, reduced power, timing codes | $1,000 - $1,800 | Medium |
Reliability Verdict
The BMW S63 (specifically the S63TU in the F10 M5 and F85 X5M) is a high-maintenance exotic engine disguised as a sedan motor. The rod bearings are a periodic maintenance item, not a lifetime part. Injectors can stick open and wash cylinder walls, destroying the block. If you treat it like a Camry, it will die. If you treat it like a Ferrari, it will thrill you.
BMW S63 V8 Reliability: The Definitive Guide
The BMW S63 is the M-Division’s sledgehammer. A 4.4L twin-turbo V8 that powers the M5, M6, X5M, X6M, and M8, it is capable of 600+ horsepower and supercar-killing performance. It is violent, responsive, and addictive.
It is also one of the most high-maintenance and financially risky V8s ever produced.
Unlike the “civilian” N63, which failed due to incompetence (bad seals, battery drain, hot-V mismanagement), the S63 fails due to physics. The tight rod bearing clearances, massive cylinder pressures, and immense heat generation require a level of maintenance that most second and third owners simply do not provide.
This guide is not a scare tactic. It is a survival manual. If you own an S63-powered BMW, or are planning to buy one, you need to understand exactly what fails, why it fails, and how to prevent it.
1. The S63 Architecture: Not Just a Tuned N63
Many people dismiss the S63 as “just an N63 with big turbos.” This is a dangerous oversimplification. While they share a block design and displacement, the S63 is extensively re-engineered for track duty.
Key Differences vs N63
- Cross-Bank Exhaust Manifold (S63TU): This is the S63’s party piece. Instead of feeding exhaust pulses into a turbo from just one bank, the S63 couples cylinders from opposite banks to create a constant, pulse-tuned flow to the twin-scroll turbos. This virtually eliminates lag.
- Cooling: The S63 has massive auxiliary radiators, engine oil coolers, and transmission coolers that the N63 lacks.
- Oiling: A unique oil sump design (and in the F90, a quasi-dry-sump system) to prevent starvation under high-G cornering.
- Pistons & Rods: Reinforced for higher boost pressures.
The Generations
- S63B44O0 (2010-2013): The original. Found in E70 X5M / E71 X6M. Based on the N63 (no Valvetronic). High Risk.
- S63B44T0 (S63TU) (2011-2017): The most common. Found in F10 M5, F12 M6, F85 X5M. Added Valvetronic, Cross-Bank Manifold, 10:1 compression. High Risk (Rod Bearings).
- S63B44T4 (S63TU4) (2018-2023): The F90 M5 engine. Revised turbos, better oiling, improved rod bearings. Moderate Risk.
2. Rod Bearing Failure: The Elephant in the Room
If you take nothing else from this guide, take this: Rod bearings on the S63TU (F10 M5, F06/F12/F13 M6, F85 X5M) are a wear item.
The Problem
BMW’s M engines (S65, S85, S63) are notorious for using dangerously tight rod bearing clearances combined with thick 10W-60 oil (in earlier engines) or long service intervals (in newer ones). In the S63TU, the clearance is so tight that reliable lubrication at high RPM requires perfect oil condition.
The Failure Mechanism
- Long Intervals: BMW’s recommended 10,000-mile oil changes are death for this engine. The oil shears down, fuel dilution occurs, and the additive pack depletes.
- Metal-to-Metal: Under high load, the oil film breaks down. The rod bearings (made of a lead-copper alloy or later tin-aluminum) physically contact the crankshaft journal.
- Spun Bearing: Friction spikes, the bearing welds itself to the crank, and spins inside the connecting rod.
- Carnage: The rod cap distorts, oil pressure hits zero, and the engine seizes.
Symptoms
- None. Often, there is no warning until it happens.
- Knocking: A rhythmic “thud-thud-thud” from the bottom end that speeds up with RPM.
- Glitter in Oil: Cutting open the oil filter reveals copper or silver flakes.
The Solution: Preventive Replacement
Do not wait for a noise.
- Interval: Replace rod bearings every 60,000 - 80,000 miles.
- Cost: $2,500 - $3,500 at an independent M-specialist.
- Upgrade: Use aftermarket bearings (ACL, BE Bearings) with slightly increased clearance and ARP rod bolts.
[!CRITICAL] If you buy an F10 M5 with 70,000 miles and no proof of bearing service, trailer it to the shop. Do not drive it home.
3. Fuel Injector Washout: The Silent Killer
The S63 uses Bosch piezo-electric direct injectors (up to 2017) or solenoid injectors (F90). The piezo injectors (Index 11 and earlier) are prone to leaking.
The Failure
A piezo stack fails, causing the injector to stick open. It sprays fuel continuously into the cylinder, even when the valve is closed.
The Consequence: “Washout”
- Oil Dilution: The excess fuel washes the oil film off the cylinder walls.
- Scoring: The piston rings drag against dry metal, scouring the Alusil lining.
- Hydro-lock: In extreme cases, the cylinder fills with liquid fuel. When the piston comes up, liquid doesn’t compress. The rod bends or snaps, punching a hole in the block.
- Bearing Death: Fuel-diluted oil destroys the rod bearings in record time.
The Fix: Index 12
BMW updated the injectors multiple times. The heavy-duty “Index 12” injectors are significantly more reliable.
- Check: Pull the engine cover and look at the injector stems. The index number is the last two digits (e.g., “-09”, “-11”, “-12”).
- Replace: If you have Index 11 or lower, replace them all.
- Cost: Current cost for a set of 8 Index 12 injectors is $2,500 - $4,000.
4. Crank Hub Slip: The S55 Virus Spreads
While famous on the M3/M4 (S55 engine), the Spun Crank Hub is highly prevalent on the S63TU, especially when tuned.
The Design Flaw
The crankshaft timing gear is not keyed to the crank. It is held on by the friction of a single central bolt.
- High Load: When the DCT transmission shifts aggressively (kickdown) or the engine is tuned for massive torque, the sudden change in rotational mass overcomes the friction washer.
- Slip: The timing gear slips relative to the crank.
- Timing Jump: The cams are now out of sync with the pistons. The pistons smash into the valves.
Prevention
- Stock Power: Rare failure, but possible on aggressive downshifts.
- Stage 1/2 Tune: High Risk.
- Solution: Install a Pinned Crank Hub or a Capture Plate. A pinned hub physically locks the gear to the crank.
- Cost: $3,500 - $5,000 (requires dropping the oil pan and front subframe).
5. Maintenance Schedule: The “M-Tax”
You cannot maintain an S63 like a 530i. If you follow the iDrive service intervals, you will destroy the engine.
The Enthusiast Schedule
| Service | BMW Interval | Verified “Safe” Interval | Cost (Indie) |
|---|---|---|---|
| Engine Oil | 10,000 miles | 3,000 - 5,000 miles | $200 |
| Spark Plugs | 30,000 miles | 15,000 - 20,000 miles | $600 |
| Ignition Coils | As Needed | 30,000 - 40,000 miles | $500 |
| Transmission Fluid | Lifetime | 30,000 miles (DCT) | $800 |
| Diff Fluid | 30,000 miles | 15,000 miles | $250 |
| Coolant Flush | Lifetime | 3 years | $300 |
| Injectors | As Needed | Proactive (Index 12) | $3,500 |
| Rod Bearings | Never | 60,000 miles | $3,000 |
Why so frequent?
- Oil: The turbos cook the oil. It degrades fast. 3,000 miles is cheap insurance against a $25,000 engine.
- Plugs/Coils: High boost eats ignition components. A misfire at 20psi can crack a ring land.
6. The Evolution: S63 vs S63TU vs S63TU4
Not all S63s are created equal.
S63B44O0 (2010-2013 X5M/X6M)
The “Beta Test.” Based on the original N63.
- Pros: Cheapest entry into an M V8.
- Cons: No Valvetronic (worse throttle response), old injectors, terrifying reliability.
- Verdict: Avoid unless you are a mechanic.
S63B44T0 “TU” (2012-2017 M5/M6/X5M)
The “Rod Bearing Eater.”
- Pros: Incredible performance, Cross-Bank Manifold sound, massive tuning potential.
- Cons: Peak rod bearing risk. Peak injector risk.
- Verdict: The sweet spot for value, provided you do the bearings IMMEDIATELY.
S63B44T4 “TU4” (2018-2023 F90 M5)
The “Refined Beast.”
- Pros: Revised oiling, stronger rods, improved bearings, solenoid injectors (reliable!).
- Cons: Coolant expansion tank leaks are the main issue. Still complex.
- Verdict: The most reliable S63. If you can afford an F90, get it.
7. Cost of Ownership Analysis
Let’s look at a real-world scenario: Buying a 60,000-mile 2014 BMW M5 (F10) and driving it to 100,000 miles.
Phase 1: The Purchase & “Baselining” ($4,500)
You buy the car. You must immediately assume the previous owner did nothing.
- Rod Bearings: $3,000
- Fluids (Oil, Diff, DCT): $1,000
- Plugs/Filters: $500
Phase 2: The ownership (60k-80k) ($4,000)
- Tires: $1,500 (Michelin PS4S are mandatory).
- Brakes: $1,500 (Rotors are massive and expensive).
- Suspension Arms: $1,000 (Thrust arm bushings fail).
Phase 3: The Big Items (80k-100k) ($5,000)
- Injectors: $3,000 (If not already Index 12).
- Turbo Coolant Lines: $1,000 (Rubber lines rot).
- PCV/Breathers: $1,000.
Total Projected Maintenance (4 Years): $13,500 Annual Cost: $3,375 (Excluding fuel and insurance).
This is the “M-Tax.” If you cannot afford $3k/year in maintenance, you cannot afford an M5.
8. S63 vs The Competition
S63 vs BMW N63
The N63 is a mess of valve stem seals and timing chains. The S63 fixes most of the N63’s “stupid” problems (stem seals are rare on S63) but introductes “high stress” problems (rod bearings).
- Winner: S63 (If maintained). The internals are far higher quality.
S63 vs Mercedes M157/M278
The Mercedes 5.5L BiTurbo (M157) is a tank. It doesn’t eat rod bearings. It doesn’t wash out cylinders. It just eats engine mounts and timing chains (at high miles).
- Reliability: Mercedes M157 > BMW S63.
- Fun: BMW S63 > Mercedes M157.
S63 vs Audi 4.0T
The Audi 4.0T (RS7) has the turbo oil screen issue. Once that is fixed (or recalled), the Audi block is arguably stouter than the S63TU.
- Reliability: Tie (both have one catastrophic flaw).
9. Tuning Risks: Going Beyond Stock
The S63TU is easily capable of 700hp with a downpipe and tune. But reliability drops off a cliff.
- Stage 1 (Tune only): Generally safe, providing maintenance is perfect.
- Stage 2 (Downpipes + Tune): Torque spikes massively. Crank Hub Slip becomes a real danger. Rod bearing stress increases.
- Upgrade Required: If you go Stage 2, you must pin the crank hub and run a 3,000-mile oil interval.
[!WARNING] Burble Tunes: DO NOT run aggressive “burble” or “pop bang” tunes. They dump raw fuel into the exhaust, washing cylinder walls and destroying catalytic converters. It is the fastest way to kill an S63.
10. Conclusion: Should You Buy One?
The BMW S63 is a masterpiece of engineering, but it is a race engine at heart. It does not tolerate neglect.
Buy an S63 if:
- You have $5,000 set aside for immediate baselining (Bearings/Injectors).
- You are religious about warm-up procedures (never go over 3k RPM until oil is 180°F).
- You want the absolute pinnacle of V8 performance sedan excitement.
Avoid an S63 if:
- You are stretching your budget to buy the car.
- You trust “Lifetime” fluids.
- You want a “start and go” daily driver.
In the world of super-sedans, you pay for what you get. With the S63, you pay in maintenance, but you are rewarded with one of the greatest internal combustion experiences on earth.
Expert Buying Advice
Budget $3,000 immediately for preventive rod bearings on any F10 M5 or F85 X5M over 60k miles. Check injector index (must be Index 12). Avoid tuned examples unless the crank hub has been pinned. The F90 M5 (S63TU4) is significantly more robust but still requires 'M-tax' maintenance.