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BMW N63 vs S63: Which V8 is Less of a Disaster?

BMW N63 vs S63: Which V8 is Less of a Disaster?

Reliability Score

50/100

Based on owner reports and frequency of repairs.

Published on: Sun Feb 15 2026

BMW N63 vs S63: Which V8 is Less of a Disaster?

You are looking at a used BMW V8. Maybe a 550i (N63) vs an M5 (S63). Or an X5 50i vs an X5M.

They look similar. They sound similar. They are both 4.4L Twin-Turbo Hot-V V8s.

But their reliability profiles are completely different.

The N63 is widely considered one of the least reliable engines BMW ever made. The S63 is a high-strung exotic that requires “M-Tax” maintenance.

Which poison do you pick?

1. Architecture: Same Block, Different Guts

  • Block: Both use the same Alusil block architecture.
  • Turbos: Both use a Hot-V layout.
  • Heads:
    • N63: Conventional cylinder heads.
    • S63: Optimized for high flow.
    • S63TU: Features the glorious Cross-Bank Exhaust Manifold for pulse tuning.

The Critical Difference: Cooling

This is where the N63 failed. The original N63 had inadequate cooling for the turbos in the V. The heat cooked the valve stem seals, vacuum lines, and injectors. The S63 has massive auxiliary radiators and oil coolers. It manages heat significantly better.

2. Failure Modes: N63 (The “Civilian”)

The N63 (especially 2009-2013) fails from Heat Soak.

  1. Valve Stem Seals: They harden and crack. The engine sucks oil. You see blue smoke at idle. Cost: $6,000+.
  2. Timing Chains: The chains stretch. The dealership replaces the engine.
  3. Battery Drain: The cooling fans run for 20 minutes after you park to try and save the turbos. This kills the battery.
  4. Injectors: Index 11 failures wash the cylinders.

Verdict: The N63 is a “death by a thousand cuts.” It leaks, it smokes, it rattles.

3. Failure Modes: S63 (The “Military Grade”)

The S63 (M-Division) fails from Stress.

  1. Rod Bearings: The #1 killer. Tight clearances + thick oil + high G-force + 7,000 RPM redline = spun bearings.
  2. Injectors: Same piezo injector risk as the N63.
  3. Crank Hub (S63TU): Can slip on tuned engines.
  4. Valve Stem Seals: RARE. The S63 runs cooler cylinder head temps and uses better seal material.

Verdict: The S63 is “death by one big bang.” It generally doesn’t smoke or leak like the N63. It just seizes if you ignore the bearings.

4. Cost to Own

Let’s assume you drive both to 100,000 miles.

N63 Owner

  • Valve Stem Seals: $6,000
  • Injectors: $3,000
  • Turbo Coolant Lines: $1,500
  • Oil Top-ups (1qt/500mi): $1,000
  • Total: $11,500 (Plus extreme frustration).

S63 Owner

  • Rod Bearings (Preventive): $3,000
  • Injectors: $3,000
  • Diff/Trans Fluids: $1,000
  • Tires/Brakes (M-Tax): $4,000
  • Total: $11,000 (Plus extreme joy).

5. Which one is “Better”?

The S63 is the better engine. It is built with stronger internals, better cooling, and (in the TU version) exponentially better throttle response.

Its failures (bearings) are predictable. You can change them and be safe. The N63’s failures (seals, consumption, chains) are chronic. You fix one, another appears.

Exception: The N63TU3 (2018+ M550i) is actually very good. It solved most N63 issues. But the original N63 is a hard avoid.

6. Buying Advice

  • Avoid: 2009-2013 N63 (550i, 750i, X5 50i). Just don’t.
  • Caution: 2014-2017 N63TU. Better, but still check chains.
  • Buy (With Budget): S63TU (M5, X5M). Budget $3k for bearings immediately.
  • Buy (Safe): S63TU4 (F90 M5) or N63TU3 (G30 M550i).