2016 — 2019
4.7L Bi-Turbo V8 (M278) - GLS 500
Petrol
While driving at low speeds, carefully listen for any 'clunking' noises from the front end, as the air suspension struts on the X166 platform can occasionally show signs of wear as they age.
Check this by idling the engine with the bonnet open and listening for any 'ticking' or 'rattling' from the top of the engine; the M278 V8 has complex timing gear that appreciates a consistent, high-quality oil change history.
While stationary, cycle the infotainment screen through the various air suspension height settings to ensure the compressor lifts the vehicle smoothly without any warning messages appearing on the dash.
Before turning the engine off, spend a moment observing the transmission shift quality between 1st and 3rd gears to ensure transitions are seamless, as the 9G-TRONIC gearbox is sensitive to its fluid health.
Typically the point for the first major transmission fluid service and potential inspection of auxiliary drive belts.
A common window where the air suspension components and engine mounts may require a professional inspection to ensure the ride quality remains premium.
Consider having the turbocharger cooling system and vacuum lines thoroughly inspected to maintain optimal performance of the Bi-Turbo V8.
Ensure the service history shows oil changes every 10,000km or annually, regardless of what the computer suggests.
Check for any signs of weeping around the engine valve covers, which is helpful to catch early during routine servicing.
Verify that the panoramic sunroof seals have been cleaned and lubricated to prevent any potential drainage issues.
Keep a close eye on the front brake rotors and pads, as the GLS 500 carries significant weight and consumes these items steadily.
Ensure the coolant has been flushed per the manufacturer's recommendation to protect the longevity of the Bi-Turbo system.
Estimated repair costs if issues arise
If this component needs attention in the future, it involves replacing the air struts or compressor. Depending on the car's history, you might eventually need to budget for this as the rubber seals age over time.
On the M278 engine, if you notice a cold-start rattle that persists, it is wise to have the tensioners inspected. In cars of this age, it is common to consider preventative maintenance to ensure the timing system stays in peak condition.
To keep the 9G-TRONIC shifting smoothly, a full fluid and filter service is recommended. Future budget planning for this maintenance will ensure the longevity of your drivetrain.
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Disclaimer: This report is generated with the assistance of AI analysis based on verified automotive data. While we strive for 100% accuracy, enthusiasts should always conduct physical inspections and consult service records. View Full Disclaimer