When to replace spark plugs in a Mercedes-Benz G-Class AMG
Mercedes-Benz G-Class AMG
Mercedes-Benz G-Class AMG•
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Replace Mercedes-Benz G-Class AMG spark plugs according to the schedule for the specific engine, observing mileage and any time limit. Misfires, hesitation and fault codes require investigation before scheduled replacement. The G 63 needs petrol-engine spark plugs: glow plugs belong to diesel G-Class models, including those with AMG Line trim.
This article focuses on the G 63 with the 4.0-litre petrol V8 and updated versions with an integrated starter-generator. Their part numbers and service intervals must not be carried over to earlier G-Class AMG models. Confirm the VIN, model year and engine before ordering. A body kit or AMG badge does not establish these details.
Which plugs different G-Class versions use
The Mercedes-AMG G 63 description specifies a 4.0-litre petrol biturbo V8; the updated version pairs it with a starter-generator. Parts selection requires the complete vehicle identification. The table separates the main cases and does not replace a VIN-based application check.
| Version | Plug type | What matters |
|---|---|---|
| G 63 with the 4.0-litre V8 | Spark plugs | Select by engine and model year |
| G 63 with a starter-generator | Spark plugs | Electric assistance retains spark ignition |
| Earlier G-Class AMG models | Spark plugs | Verify the parts and schedule separately |
| G 450 d with AMG Line | Glow plugs | This diesel version is not a G 63 |
| Vehicle with an AMG body kit | Engine-specific | Appearance does not identify the system |
The petrol G 63
A spark plug creates a spark inside the cylinder using high voltage from the ignition coil. As its electrodes wear, maintaining reliable ignition becomes harder. An engine can therefore idle smoothly but misfire during acceleration. Such behaviour should not be dismissed as part of an AMG’s sporting character.
The G 63 with a starter-generator
Electric assistance does not remove the petrol V8’s need for spark ignition. This version still requires the correct plugs, functioning coils and combustion-engine servicing. The Mild Hybrid designation does not authorise a longer replacement interval. Servicing must also account for the possibility of an automatic engine start.
Diesel G-Class models with AMG Line
For example, the G 450 d AMG Line is a diesel with a styling package, rather than a G 63. Diesel fuel ignites in air heated by compression. Glow plugs help during starting and, depending on the control strategy, afterwards. They require different parts and diagnostic methods.
Signs that the plugs need checking
Petrol engine misfires
- Uneven running and pronounced shaking have appeared after starting.
- Acceleration brings repeated hesitation or noticeable losses of power.
- Starting takes longer and engine fault codes have appeared.
None of these signs proves that a plug has failed. A coil, injector, intake leak or mechanical cylinder problem may be responsible. On a G 63, distinguish combustion misfires from vibration through mounts or the drivetrain. Record whether the complaint occurs after parking, when warm or under load.
Glow system problems on diesel versions
On a diesel G-Class, difficult starting, rough initial running and glow circuit faults justify investigation. Similar symptoms can result from power-supply, wiring or controller faults. Warm weather may mask a problem, but it does not establish that the system works correctly.
Why plugs can fail before their scheduled replacement
A new plug will not repair an oil leak, an injection fault or a damaged coil boot. If a fault quickly returns to the same cylinder, find the underlying cause rather than repeating the replacement without testing. Comparing removed plugs across cylinders can help.
| Cause | Possible effect | Checks |
|---|---|---|
| Wear or incorrect gap | Unstable ignition | Application and plug mileage |
| Oil in a plug well | Insulation or boot damage | Seals and ignition coil |
| Combustion problems or oil consumption | Electrode deposits | Injection and cylinder condition |
| Glow supply fault | Insufficient or excessive heating | Wiring, connectors and controller |
| Installation error | Thread or seat damage | Procedure and tightening torque |
For a G-Class that frequently idles, makes short trips or operates in dust, check the schedule’s special operating requirements. There is no universal rule to halve every plug interval in hot weather. Tell the workshop about engine software changes or other modifications: a tuning-catalogue suggestion should not replace a proper application check.
Why diagnosis should not be delayed
Severe misfires can allow unburned fuel into the exhaust and overheat the catalytic converter. Acceleration also deteriorates. Continuing to load the engine by pressing the accelerator harder to overcome hesitation is unwise.
For a diesel glow system, first establish which circuit is affected. Smooth running once warm does not prove the glow plugs are healthy. Equally, one fault code does not justify replacing every plug and the controller without checking them.
Important. If the engine warning flashes, the vehicle shakes severely or power drops sharply, stop accelerating and pull over safely. If pronounced misfiring persists, arrange diagnosis and recovery.
How to establish the interval and select the parts
The schedule and service history
Do not assign one interval to every G-Class AMG. Request the spark plug replacement operation from the VIN-specific schedule, accounting for the engine, model year and original specification. A time limit remains relevant even when the vehicle covers little mileage.
ASSYST PLUS helps plan servicing, but a Service A or Service B entry does not itself confirm plug replacement. Ask for an invoice showing the date, mileage, quantity and part numbers. If previous work lacks detailed records, reconstruct the history and establish the applicable schedule first.
An AMG requires the main vehicle manual together with its applicable supplement. For example, the AMG supplement to the 2024 G-Class manual describes variant-specific features, but does not replace the main document or individual maintenance schedule. For a diesel G-Class, establish separately whether scheduled glow plug replacement is specified.
What to verify before buying
| Parameter | Spark plug | Glow plug |
|---|---|---|
| Application | VIN, engine, model year | VIN, engine, glow system |
| Operating specification | Heat range, electrodes, gap | Voltage and heater design |
| Geometry | Thread, reach, seat | Thread, tip, seat, connector |
| Installation | Torque and fitting conditions | Removal and fitting procedure |
Cylinder count alone is not enough to order a set: ignition arrangements and parts applications differ between engines. An iridium label or a similar-looking thread is not sufficient either. Confirm the current part number and official supersessions; take gap and torque requirements from the procedure for the particular engine.
How to assess an unknown service history
When comparing current listings for the Mercedes-Benz G-Class AMG, ask about the last plug replacement as well as the latest service. Request records of engine modifications, where fitted. A body kit, replacement badge or seller’s description does not establish the variant: check the VIN and vehicle documents.
What removed plugs can reveal
Keep removed spark plugs in cylinder order. A marked difference between one plug and the others helps direct the investigation. Insulator colour and deposits alone cannot give a definitive diagnosis: compare them with fault codes, oil consumption and measurements.
| Observation | Possible meaning | Next check |
|---|---|---|
| Heavy deposits on one plug | A local combustion problem | That cylinder and its injector |
| Crack or flashover marks | Insulation damage | Plug, coil boot and coil |
| Oil outside the plug above its seat | Leak into the plug well | Seals; distinguish this from oil in the cylinder |
| Glow circuit fault | Plug, wiring or control fault | Electrical tests before removal |
On a diesel G-Class, do not remove glow plugs simply for a visual inspection whenever starting is poor. Test the electrical system first. If removal is necessary, assess seizure risk and tip integrity. If a plug breaks, establish where its missing fragment is located.
Diagnosis and preparation for replacement
The diagnostic sequence
- Save fault codes and their operating conditions before clearing the control unit’s memory.
- Check the power supply, connectors and accessible connections. Inspect coils and plug wells on petrol engines, or glow circuits on diesels.
- Perform the engine-specific tests. Check injection, intake sealing and cylinder condition where required.
- After repairs, check operation under the original complaint conditions and look for returning faults. Record the date, mileage and fitted parts.
Pre-work checklist
☐ Confirm the engine, plug type, part number and quantity by VIN.
☐ Prepare the correct tools and replacement procedure.
☐ Prevent an automatic engine start and follow the vehicle’s electrical-system procedure.
☐ Clean the work area and protect openings from sand and debris.
☐ Agree additional parts after checking their condition.
Correct tightening matters for sealing and heat transfer. Both insufficient and excessive torque can damage a plug. The installation procedure determines engine temperature, lubrication and any gap adjustment. Diesel removal also has specific force limits: applying a longer lever to a seized glow plug risks breakage.
Selection and installation mistakes
- Treating a diesel G-Class with AMG Line as a petrol G 63.
- Copying part numbers and intervals from a different G-Class AMG engine.
- Selecting plugs solely by electrode material or visual similarity.
- Testing an unidentified glow plug by connecting it directly to the battery.
- Clearing faults before saving data and replacing every coil without testing.
Frequently asked questions about spark plugs
Is there one replacement interval for all G-Class AMG models
No. The schedule depends on the engine and model year. Where both distance and time limits are specified, observe both. Severe misfiring requires diagnosis without waiting for the next scheduled service.
Does a G 63 with electric assistance still need spark plugs
Yes. The starter-generator assists the petrol engine but does not replace the spark inside its cylinders. Plug servicing remains necessary. A longer interval due to the hybrid system requires an explicit provision in the applicable schedule.
Must coils be replaced with the spark plugs
Not automatically. Check coils and boots separately. A damaged coil may need replacement, but healthy parts do not become mandatory service items whenever the plugs are renewed. If a complete set is proposed, ask what diagnostic findings justify it.
Glow plugs on a diesel G-Class with AMG Line
Does the G 63 use glow plugs
The petrol Mercedes-AMG G 63 uses spark plugs, not glow plugs. Glow plugs belong to diesel G-Class models, such as the G 450 d with AMG Line. Confirm the engine first, even if an AMG badge is fitted to the body.
Should the glow system be checked in hot weather
Yes, when there are faults or starting complaints. Warm conditions can make symptoms less obvious, but do not repair a circuit defect. On a modern diesel, glow operation may also continue after starting. Assess the system using its test procedure, rather than the weather alone.
Why can a glow fault return after replacement
An unsuitable plug, poor connection, damaged wiring or the controller may be responsible. Distinguish an old stored record from a new active fault. Erasing a code alone does not establish that the repair is complete.
Should one glow plug or the whole set be replaced
Decide after checking the other circuits and assessing the parts. Similar age and difficult access may justify replacing a set. One failed plug does not prove that all have failed; also consider the risks of removing healthy components.
Conclusion
For a Mercedes-Benz G-Class AMG, begin by confirming the engine and variant using the VIN. The petrol G 63 needs spark plugs, including versions with a starter-generator. A diesel G-Class with AMG Line follows its own glow-system requirements. Establish the replacement interval, parts and repair scope from the documentation, service history and diagnostic findings.
