Mercedes-AMG M177 Engine Reliability: Oil Leak Epidemic & Stone Damage Reality

Published on: Sun Jan 18 2026

1. This Engine Powers More Cars Than You Think

The Mercedes-AMG M177 4.0L twin-turbocharged V8 appears in:

• C63 W205 (2015–2021, 469–503 hp)
• E63 W213 (2017–2023, 603 hp)
• AMG GT / GT S (2015–2023, 469–550 hp)
• AMG GT 4-Door (2018–2023, 577–630 hp)
• CLS 63 AMG (2018–2023, 577 hp)
• S63 AMG (2017–2020, 603 hp)
• GLE 63 AMG (2020–2023, 603 hp)
• GLS 63 AMG (2020–2023, 603 hp)

What this means:

Buying a different Mercedes-AMG model does not save you from M177 engine risk.

The valve cover oil leaks that plague a C63 W205 at 55,000 miles will plague an E63 W213 at 52,000 miles.

The thermostat failure that checks your engine light in an AMG GT is the same thermostat in the S63.

The engine follows you.

2. Reliability Score: 66/100

Classification: High Maintenance / Leaky

Score Breakdown:

• Engine Reliability: 20/30 (Strong mechanicals, but plagued by gasket/seal failures)
• Drivetrain: 22/25 (MCT transmission is tough, diffs are solid)
• Electronics: 16/20 (COMAND glitches, sensor faults)
• Maintenance Cost: 8/25 (Very high; “AMG Tax” is real, and it needs frequent sealing)

[!WARNING] Oil Leaks are Guaranteed. The M177 is notorious for valve cover, oil separator, and cam cover leaks. These are not “if” but “when.”

3. The Psychological Reality of M177 Ownership

Owner Anxiety: The “Oil Smell” Paranoia

What Every M177 Owner Lives With

Owning an M177-powered AMG means living with the constant suspicion that your car is bleeding fluids.

The Daily Mental Load:

Every time you park:

• You look back at the ground for oil drops.
• You sniff the air near the wheel arches (buring oil smell = valve covers leaking).
• You check the coolant reservoir (looking for stone damage leaks).

Every time you drive hard:

• You wonder: “Is that smell me?”
• You calculate: “Is the thermostat going to stick open today?”
• You second-guess: “Should I have installed radiator guards?”

What Owners Say:

“I love the V8 rumble, but I hate the smell. I can’t drive it with the windows down because the burning oil smell gives me a headache. Dealer quoted $4,000 to reseal everything.” — C63 W205 owner, 55,000 miles, MBWorld

“Failed thermostat at 40k. Failed coil pack at 48k. Leaking valve covers at 52k. It feels like the engine is slowly dismantling itself.” — E63 W213 English owner

The Difference Between “Fast” and “Reliable”:

Your AMG might:

• Run 0-60 in 3.8 seconds ✓
• Sound incredible ✓
• Look pristine ✓

And still be leaking from three different gaskets.

Gaskets fail silently until they drip on the exhaust. By then, the mess is comprehensive.

4. Failure Progression Narratives: How Owners Make the Wrong Decision

Valve Cover & Cam Seal Leaks: The “Messy Engine” Reality

Phase 1: Seeping (Months 1–12)

The RTV sealant and rubber gaskets on the cam covers harden from V8 heat. Oil begins to sweat out.

What you notice: A faint whiff of oil when you park in a garage.
What you think: “Probably just a spilled drop from the last oil change.”
What’s actually happening: The seals have failed. Oil is coating the side of the engine.

Phase 2: The Drip (Ignored)

You see a small spot on the driveway. The smell is stronger. You add a quart of oil every 2,000 miles.

What you notice: Visible spot. frequent smell.
What you think: “It’s an AMG, they burn a little oil. I’ll clear it up later.”
What’s actually happening: Oil is saturating the coil packs and wiring harness.

Phase 3: The Repair Bill Shock

You take it in for a service. The tech sends you a video: “Engine serves as an oil fountain.”

The Financial Aftermath:

• Reseal Job (Dealer): $3,500–$5,000 (Engine-out or heavy disassembly often quoted)
• Reseal Job (Indy): $1,500–$2,500
• Total: $1,500–$5,000 for rubber seals.

The Decision Mistake: Owners delay the reseal. The oil degrades rubber hoses and wiring insulation, leading to electrical gremlins later.

Radiator Stone Damage: The Design Flaw You Can’t Control

Phase 1: The Impact

You are following a truck on the highway. Ping. A small stone hits the wide-open front grille.

What you notice: Nothing immediately.
What you think: “Just a rock chip on the bumper.”
What’s actually happening: The stone punctured the auxiliary radiator or transmission cooler, which has zero mesh confusion.

Phase 2: The Bleed Out

Coolant slowly sprays out. You get a “Low Coolant” warning the next day.

What you notice: Warning light.
What you think: “I’ll just top it up.”
What’s actually happening: The system is losing pressure. Engine efficiency drops.

Phase 3: Overheat & Tow

You push the car hard. The leak expands. “Engine Overheating – Stop Vehicle.”

The Financial Aftermath:

• New Radiator/Cooler: $800
• Labor (Bumper off): $1,200
• Towing: $200
• Total: $2,200 because Mercedes didn’t put a $5 mesh screen in front.

The Decision Mistake: Not installing aftermarket radiator guards immediately upon purchase.

5. Why This Is Not a “Lemon Problem”

You Cannot “Find a Dry One”

The Myth: “I’ll buy a low-mileage C63 and it won’t leak.”

The Reality: Leaks are inevitable on the M177.

Gasket Failure:

• Caused by: High heat density in a compact V8 bay vs. rubber materials.
• Affects: Every M177 eventually. 40k miles, 60k miles—it’s coming.

Thermostat Failure:

• Caused by: Component quality.
• Affects: Widespread numbers of W205/W213 cars.

You cannot avoid this by “buying a good one.” You are buying a leak maintenance schedule.

6. Why Preventive Maintenance Is Not a Shield

Fixing One Leak ≠ Dry Engine

What owners think: “I just paid $3,000 to reseal the valve covers. Now I’m done with leaks.”

The reality: You fixed the top leaks. The bottom leaks are next.

Residual risks after reseal:

• Oil Pan Gasket: Shifts point of failure to the next weakest seal.
• Rear Main Seal: Can start leaking as internal pressure changes.
• Turbo Oil Lines: Can crack during the valve cover repair manipulation.

Preventive maintenance reduces the mess, but the M177 is a “wet” engine by nature.

The $10,000 Maintenance Reality

To properly maintain an M177 to 100,000 miles:

Preventive maintenance is not a shield. It’s a substrate of cash you burn to keep the car on the road.

7. Mileage Milestones: What WILL Fail

0 – 40,000 Miles

Outlook: “Factory Fresh.”

• Risks: Thermostat failure, random stone damage to radiators.
• Action: Install radiator guards ($300).

40,000 – 70,000 Miles

Outlook: “The Leaky Phase.”

• Risks: Valve Cover Leaks. Engine Mounts collapse.
• Action: Budget $3,000 for resealing and mounts.

70,000 – 100,000 Miles

Outlook: “Drivetrain Wear.”

• Risks: Turbo seals, Diff leaks, Suspension arms.
• Action: Refresh suspension, check turbo play.

8. Frequently Failing Parts (Technical Detail)

9. Frequently Asked Questions

Q: Is the M177 engine reliable? A: Mechanically (pistons, rods, crank), yes. It acts like a tank. But the things attached to it (gaskets, sensors, plastic pipes) are fragile. It won’t explode, but it will bleed.

Q: C63 vs M3 Reliability? A: M3 (S55) has the Crank Hub “Explosion” risk. C63 (M177) has the “Death by a Thousand Leaks” risk. M3 is a roulette wheel; C63 is a subscription service to your mechanic.

Q: Can I drive with the oil smell? A: You can, but it’s unpleasant, healthy hazard, and embarrassing. An AMG shouldn’t smell like a 1990s tractor.

Q: Will an aftermarket warranty cover these leaks? A: Maybe. Read the fine print. Many exclude “seals and gaskets” or “hoses.” If they do cover it, it’s worth its weight in gold for an M177.

10. Related Vehicle Guides

This engine appears in the following vehicles:

• Mercedes C-Class Reliability (Note: Covers C-Class platform; M177 specific leaks apply to AMG C63 models described here)

Compare with other high-anxiety engines:

• BMW S63 Engine Reliability (M5, X5 M)
• Audi 2.9T Engine Reliability (RS5, RS4)