The 2017 G550 with the M278 5.5L biturbo V8 is a solid platform but suffers from expensive engine internal failures tied to manufacturing defects in early M278 engines, plus typical Mercedes transmission and cooling system issues. When they run well, they're tanks—but when the engine lets go, it's catastrophic.
Symptoms: Excessive oil consumption (1qt per 500-1000 miles), Blue smoke on cold start, Loss of compression in one or more cylinders, Rough idle and misfires, Check engine light with multiple misfire codes
Fix: The M278 has a known defect where inadequate piston skirt clearance causes cylinder wall scoring and piston failure. Requires complete engine rebuild or replacement. Short block replacement is 35-45 hours, full rebuild is 50-60 hours. Many shops won't tackle the rebuild—they swap in a reman long block.
Estimated cost: $18,000-35,000
Transmission Oil Cooler Failure
Common · high severity
Typical onset: 60,000-100,000 mi
Symptoms: Transmission fluid mixing with coolant (strawberry milkshake in expansion tank), Transmission slipping or erratic shifting, Overheating warning, Pink residue in coolant reservoir
Fix: The 7G-Tronic transmission oil cooler integrated into the radiator fails internally, allowing coolant and ATF to cross-contaminate. This ruins both the transmission and cooling system. Must replace radiator, flush entire cooling system, replace transmission fluid and filter, sometimes transmission if contamination went too far. 8-12 hours labor if caught early, but if transmission is damaged, add another 18-25 hours for trans rebuild/replacement.
Symptoms: Clunk or thud when shifting from Park to Drive/Reverse, Excessive drivetrain vibration at idle, Harsh engagement into gear, Visible sagging of transmission on inspection
Fix: The hydraulic transmission mounts fail and leak fluid, causing harsh shifting and vibration. The G-Class transmission mount is particularly stressed due to vehicle weight and off-road use. Replacement requires supporting the transmission and unbolting old mounts. 3-4 hours labor for both mounts.
Estimated cost: $800-1,400
Fuel Filter Housing Corrosion and Leaks
Occasional · medium severity
Typical onset: 70,000-110,000 mi
Symptoms: Fuel smell in cabin or under vehicle, Visible fuel weeping from filter housing area, Hard starting or stumbling, Check engine light with fuel system lean codes
Fix: The plastic fuel filter housing cracks or the aluminum components corrode where dissimilar metals meet, causing fuel leaks. More common in humid/salty environments. Requires replacing the entire fuel filter assembly and surrounding seals. 2-3 hours labor, but access is tight.
Estimated cost: $600-1,200
Crankshaft Position Sensor Failure
Occasional · high severity
Typical onset: any mileage (heat-related)
Symptoms: No-start condition, engine cranks but won't fire, Sudden stalling while driving, Intermittent rough running that gets worse when engine is hot, No RPM reading on dash
Fix: The crankshaft position sensor on the M278 fails due to heat exposure, leaving you stranded. It's bolted to the back of the engine near the bell housing—terrible location. Requires lifting vehicle, sometimes dropping front exhaust section for access. 2-3 hours labor for a $60 part.
Estimated cost: $350-600
Turbocharger Wastegate Rattle
Common · low severity
Typical onset: 50,000-100,000 mi
Symptoms: Rattling noise at idle or light throttle, sounds like marbles in a can, Noise disappears under boost/acceleration, No performance loss initially, Eventually progresses to boost leaks and reduced power
Fix: The wastegate actuator arm bushings wear out causing the flapper to rattle. Early on it's just annoying, but eventually causes boost control issues. Can replace just the wastegate actuators (4-5 hours per side) or full turbo replacement if bearing damage has occurred. Most people live with the rattle until turbos need replacement for other reasons.
Estimated cost: $1,200-2,000 per side (wastegate actuators), $4,000-6,000 per side (full turbo replacement)
Airmatic Suspension Compressor and Strut Failure
Occasional · medium severity
Typical onset: 80,000-120,000 mi
Symptoms: Vehicle sits low on one or more corners, Suspension compressor runs constantly, Airmatic fault warning on dash, Rough ride quality, Hissing sound from suspension area
Fix: The air suspension struts develop leaks and the compressor wears out from overwork. Front struts are 2-3 hours each, rears are 2.5-3.5 hours each. Compressor is another 2-3 hours. Often multiple components fail together. OE parts are stupid expensive; quality aftermarket exists but some shops won't warranty them.
Estimated cost: $1,800-2,800 per strut, $1,500-2,200 for compressor
Owner tips
Check oil consumption religiously—if you're adding more than a quart between changes, get a leak-down test before the engine grenades itself
Inspect coolant reservoir regularly for any pink/brown discoloration indicating transmission cooler failure—catching this early saves the transmission
Use MB-approved 229.5 spec oil only and change every 5,000 miles regardless of what the computer says—these engines don't tolerate extended intervals
Budget $3,000-5,000 per year for maintenance and repairs after 60,000 miles; these are not cheap to own
Have a pre-purchase inspection include a borescope inspection of cylinder walls if buying used—this catches piston scoring before you own the problem
Only buy if you have a $10K emergency fund for the inevitable engine or transmission failure, or you're getting one so cheap that a reman engine is already factored in—these are exceptional trucks when running, but the M278 engine is a ticking time bomb.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.
Fitment notes: AGM battery required; located in engine compartment passenger side
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Every control module on the 2013-2017 Mercedes-Benz G-Class — where it lives, replacement time, and what it takes to program a replacement. Modules marked dealer / factory tool won't work after a part swap alone — budget for programming.
Aftermarket tool coverage varies by software version and vehicle build — treat "aftermarket tool" rows as "usually possible" and verify against your tool maker's coverage list before promising a customer. Spot a wrong location or hour? Tell us — corrections ship fast here.
Size-standard part numbers — verify your connector type before buying. Rear blades are model-specific; check the package's vehicle list.
Fuel economy figures are EPA data via fueleconomy.gov (median across matching trims). Performance figures are compiled estimates for the 2017 Mercedes-Benz G-Class 5.0L V8 and can vary by trim.
🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years and Jeff Moore · Master Lexus & Toyota Mechanic · 20+ years.