Mercedes-Benz GLS 500
4.7-litre BiTurbo V8 with direct injection (CGI), 90-degree bank angle and hot-V layout — turbos sit between the cylinder banks. Timing chain and tensioners are the first thing to check on used examples: cold-start rattle is a warning sign. Alusil bores react badly to wrong oil or extended intervals; piston slap develops gradually from oil film loss, often triggered by fuel-washing injectors. Ignition coils rarely last beyond 120,000 km. The oil separator should be checked after 100,000 km — when faulty it forces oil vapour into the intake and accelerates intake valve carbon build-up. Sound character: subtle BiTurbo rumble, no naturally aspirated roar. Shorten maintenance intervals to 10,000 km, oil MB 229.5 with low Noack value. Engine long-lived with correct maintenance — problem cars are almost always those with missed oil changes.
Seven Seats, 455 hp — Most Powerful Luxury Liner
In the GLS 500 the M278 moves over 2,500 kg fully loaded with a composure other SUVs cannot match. No stress, no deliberation — the V8 simply delivers. The downside: consumption is hard to keep below 15 litres, tyre wear elevated by weight and power. Not a driver's car, more a prestige transporter. But for those who regularly need to move five or seven people quickly and comfortably, there is little better. The V8 here is not a luxury but a workhorse.
Engine Weaknesses 9
All M278 built before Feb. 2013 are affected by prematurely wearing chain tensioners. Mercedes responded with a goodwill campaign: new tensioners plus a check valve in the cylinder head.
Symptoms: Metallic rattle on cold start (2–5 seconds), later also rattling when warm and on hot restart
No M278 with over 120,000 km known without cylinder bore damage. Silitec coating is sensitive to knock. Full rebuild approximately €14,000–18,000, replacement engine approximately €20,500.
Symptoms: Increased oil consumption (1–1.6 L/1,000 km), engine knock, rough idle, brass swarf in oil
The M278 is the best-known example of Mercedes' oil migration problem. Oil seeps from the camshaft adjuster solenoid capillary-style through the entire engine wiring harness to the ECU. Costs up to €11,000 if ECU and harness both need replacing.
Symptoms: Cold-start rattle, fault codes P0010/P0011 camshaft adjuster, oil traces on connectors, sporadic engine misfires, complete ECU failure
CGI direct injectors carbon up from 120,000 km and dribble after shutdown. Post-drip washes the oil film from the bore — a direct precursor to bore damage.
Symptoms: Rough idle, fuel smell after shutdown, black wet spark plugs on individual cylinders, high consumption, misfire fault codes
The wastegate linkage bush wears and initially causes rattling on cold start that develops into a permanent noise.
Symptoms: Metallic rattle from the turbo area on cold start, sluggish acceleration, P0299 boost pressure fault code
The hydraulic engine mounts on the M278 V8 lose their damping fluid after around 100,000 km. The heavy V8 (>250 kg) then causes noticeable vibrations throughout the vehicle.
Symptoms: Vibrations at idle in the cabin, clunking on throttle application and lift-off, visibly collapsed engine mount
Ignition coils fail from around 100,000 km — usually one at a time, rarely all together. Misfires on individual cylinders, MIL flashes. Left untreated, fouled plugs wash the oil film from the bore.
Symptoms: Stumble at idle and part throttle, flashing engine warning light, misfire fault codes (cylinders 5 and 7 most commonly affected), occasional fuel smell
The oil separator (crankcase ventilation) wears and feeds too much oil vapour into the intake. Accelerates intake valve carbon build-up and measurably increases oil consumption.
Symptoms: Increased oil consumption, blue smoke on cold start, oil film visible in intake pipe, smoke from exhaust after extended parking
As a pure direct-injection engine, the M278 builds up carbon deposits on the intake valves. Walnut blasting every 60,000 km is recommended.
Symptoms: Rough idle, slight power reduction, occasional misfires when cold
Vehicle Weaknesses 6
Airmatic air springs become porous and lose pressure. The compressor runs continuously, overheats and fails. High-pressure lines can show damage from as early as 38,000 km.
Software fault: during light braking, gear change 7→6 cannot complete. At low oil temperatures with 48V recuperation the engine can stall. 260,658 vehicles affected.
Rear axle carrier rusts through from inside due to inadequate internal sealing. Critical on vehicles from salt-spreading areas.
GLS 350d examples with OM642 frequently show NOx sensor failures and AdBlue injection faults, leading to power loss and engine limp mode.
Air bellows become porous and lose pressure. High-pressure lines can chafe through. Repair 400–2,500 EUR.
Brakes wear quickly due to the high vehicle weight. Front axle: 827–1,228 EUR, rear axle: 547–810 EUR per change.
Reports & Tests
216 owner complaints filed with NHTSA (2012–2019). Most reported: Engine (45), Airbags (43), Electrical (25).