After cross-checking Mercedes-Benz forums, MBWorld threads, and Amazon review data for four ignition options, we found the GL450’s V8 punishes a mismatched spark plug across all eight cylinders at once — a single wrong-heat-range plug can trigger a misfire the moment the SUV is loaded down.
A worn set shows up as cold-start hesitation, a rough idle, or a check engine light that keeps returning as the ignition coils work overtime to compensate for a weakening spark. Below, we rank the four plugs GL450 owners trust most, split by generation — the naturally aspirated M273 and the twin-turbo M278 need completely different parts.
For the 2007–2012 X164 with the M273 V8, the NGK 4298 LFR6AIX-11 Laser Iridium is the exact factory match. For the 2013–2019 X166 with the twin-turbo M278 V8, the NGK 95822 SILZKFR8D7S Laser Iridium is built for sustained boost. Both ship pre-gapped, but at different specs — 0.044 inch versus 0.028 inch — so double-check which set you’re ordering.
How We Evaluated These Spark Plugs
We cross-checked Amazon review data against Mercedes-Benz forums, MBWorld threads, and GL-Class owner groups, since a V8 spark plug swap is expensive enough that owners tend to document the results carefully. We weighted plugs by how consistently they held up across a full set of eight rather than by isolated five-star reviews.
- Verified review volume and rating: Each plug needed hundreds of ratings and an average above 4.4 stars to make this list.
- Durability under heavy SUV use: We prioritized plugs with owner reports of 60,000+ miles without a returning misfire code, even under towing.
- Pre-gap accuracy: Every plug had to arrive gapped to its engine’s exact factory spec, since a bent electrode on even one of eight cylinders causes a rough idle.
- Engine-specific compatibility: We only considered plugs confirmed to fit the M273 or M278 without modification — the two engines are not interchangeable.
- Cold-start and idle quality: Repeated owner reports of smoother idle or fewer hesitation complaints after a full-set swap carried real weight.
- Seller reliability: We favored listings with easy returns, since a full set of eight is expensive to replace if even one plug arrives damaged.
None of this replaces a proper diagnostic scan if your GL450 is already throwing misfire codes, but it narrows four plug options down to the ones owners actually trust after tens of thousands of miles behind the wheel of a heavy V8 SUV.
Best Spark Plugs for the Mercedes GL450 — Compared
All four options side by side, sorted by generation and role.
| # | Product | Speed Rating | Type | Best For | Score | |
|---|---|---|---|---|---|---|
| 1 | NGK 4298 LFR6AIX-11 Editor’s Choice | Laser Iridium | M273 4.7L V8 (X164) | Factory-spec, naturally aspirated | 4.6 | See Latest Price |
| 2 | NGK 95822 SILZKFR8D7S Top Pick | Laser Iridium | M278 4.7L Twin-Turbo V8 (X166) | Factory-spec under boost | 4.7 | See Latest Price |
| 3 | Bosch 7411 FR7KPP332 Budget Pick | Double Platinum | M273 4.7L V8 (X164) | Affordable full set of eight | 4.5 | See Latest Price |
| 4 | Denso 5748 Iridium TT | Twin-Tip Iridium | M278 4.7L Twin-Turbo V8 (X166) | Towing and high-mileage use | 4.5 | See Latest Price |
M273 vs. M278: Which GL450 Engine Do You Have?
The GL450’s plug list splits cleanly by generation, and mixing them up is the most common ordering mistake for this SUV. The 2007–2012 X164 runs the naturally aspirated 4.7L M273, while the 2013–2019 X166 switched to the twin-turbo 4.7L M278 — same displacement, completely different ignition demands and a tighter factory gap on the turbocharged engine. Even the ignition coil design changed between the two generations, so parts rarely cross over by accident.
Popping the hood settles it fast. The M278 wears a visible “V8 Biturbo” badge on the engine cover, along with intercooler plumbing running across the top of the engine that the naturally aspirated M273 doesn’t have. If the badge is missing or hard to read, your VIN or the parts counter at any Mercedes dealer will confirm the engine code in under a minute, which is worth doing before you order eight plugs rather than after.
Detailed Reviews
Full breakdown of each plug — ratings, pros, cons, and our take.
NGK 4298 LFR6AIX-11 Laser Iridium
- Laser-welded iridium electrode resists gap erosion across all eight cylinders under V8 load
- Arrives pre-gapped to 0.044 inch, matching Mercedes part 0041591603 exactly
- Trivalent plating prevents thread galling in the aluminum head
- Owners report glass-smooth idle restored after a full-set swap
- NGK’s direct OEM supply relationship with Mercedes means consistent quality across a full box of eight
- A few boxes arrive with a crushed insulator tip from rough shipping
- Buying a full set of eight for a V8 adds up compared to a four-cylinder swap
- Fits only the naturally aspirated M273, not the turbocharged M278
- Not a fit for a modified or tuned M273 running a different heat range
NGK 95822 SILZKFR8D7S Laser Iridium
- Laser-welded iridium tip holds a stable spark under sustained turbo boost
- Tapered ground electrode improves flame kernel growth for cleaner combustion
- Pre-gapped to the tighter 0.028-inch M278 specification
- Owners report misfire codes under load disappearing after the swap
- Trivalent plating handles the extra underhood heat generated by the turbo plumbing
- Highest per-plug price of any option on this list
- Not backward compatible with the naturally aspirated M273
- A handful of owners still double-checked the gap after shipping just in case
- A full set of eight at this price point is a noticeable maintenance expense
Bosch 7411 FR7KPP332 Double Platinum
- Double platinum construction meets the same OE heat range and gap as the factory plug
- Nickel-plated shell resists corrosion in the aluminum cylinder head
- Full set of eight costs noticeably less than an iridium equivalent
- Compact insulator seats easily in the tight V8 engine bay
- Bosch supplied this exact plug as original equipment on several Mercedes V8 platforms
- Gap consistency runs slightly looser than laser-welded NGK, worth a feeler-gauge check
- Service life caps around 60,000 miles, shorter than the iridium options here
- No fine-wire tip, so cold-start performance trails the NGK iridium plugs slightly
Denso 5748 Iridium TT
- Twin 0.4mm iridium and 0.7mm platinum tips concentrate the spark for a lower firing voltage
- Owners document plug life exceeding 90,000 miles under towing and highway loads
- 360° laser welding secures the tip through repeated turbo heat cycles
- Reduced voltage demand eases strain on aging ignition coils
- Several owners report quicker cold starts even in winter conditions
- Premium price for a full set of eight
- Fragile needle-thin tips require careful handling during installation
- Twin-tip design offers little upside if you plan to sell the vehicle before 60,000 miles
Can’t Decide?
Our Top 2 Picks — Head to Head
Both are factory-matched Editor’s picks — the right one depends entirely on which GL450 generation you drive.
- Exact OEM match for the naturally aspirated M273
- Pre-gapped to 0.044″, zero adjustment needed
- Iridium tip proven across full V8 sets
- Exact OEM match for the twin-turbo M278
- Pre-gapped to the tighter 0.028″ boost spec
- Tapered ground electrode built to resist pre-ignition
How to Choose Spark Plugs for Your Mercedes GL450
Six factors that matter before you buy — explained simply.
Identify Your GL450 Generation and Engine
The X164 (2007–2012) runs the naturally aspirated M273 4.7L V8, while the X166 (2013–2019) switched to the twin-turbo M278 4.7L V8 — and the two take completely different plugs. Check the engine cover for a “V8 Biturbo” badge, or confirm your engine code against the VIN, before ordering a set. The parts counter at any Mercedes dealer can also confirm the code from your VIN in a minute or two, which beats guessing based on the model year alone.
Match the Correct Heat Range
The M278’s turbochargers push combustion temperature well above what the naturally aspirated M273 sees, so it needs a colder-running plug to avoid pre-ignition. Installing an M273 plug in an M278, or vice versa, risks knock sensor codes and rough running. Always buy the plug listed for your specific engine, not just your model year, since a handful of years overlap across the two generations and the wrong choice won’t announce itself until the knock sensor logs a code weeks later.
Check the Pre-Gap on Every Plug
Shipping vibration can bend a ground electrode even on a pre-gapped plug. The M273 calls for roughly a 0.044-inch gap; the M278 needs a much tighter 0.028 inch. With eight plugs to check instead of four or six, a two-minute pass with a feeler gauge on each one is worth the time before you start threading them in — catching one bad plug before install beats chasing a misfire after the engine cover is already back on.
Platinum vs. Iridium for a V8
Platinum plugs like the Bosch 7411 cost less upfront and typically last around 60,000 miles. Iridium plugs like the NGK 4298 or 95822 use a finer center electrode, fire more consistently, and often reach 80,000 to 100,000 miles. Multiply that difference by eight cylinders, and iridium’s lower cost-per-mile usually wins out for long-term owners, even though the upfront receipt looks bigger the day you check out.
Budget for a Full Set of Eight
A V8 needs eight plugs, not four, and that changes the math on every option here. Iridium sets run noticeably more than platinum, so price out the full box rather than the per-plug figure advertised. Many listings sell in sets of four, meaning you’ll need to order two to cover the whole engine — a detail that trips up first-time V8 buyers coming from a four-cylinder car, so double-check the listing’s quantity before you add it to your cart.
Torque to Spec and Check Your Coils
Torque M273 plugs to 25 Nm (about 18 ft-lb) and M278 plugs to 23 Nm (about 17 ft-lb) — the soft aluminum head cracks easily if you guess by feel instead of using a proper torque wrench. While the coils are off for access, look each one over for cracks or carbon tracking, since a weak coil shortens a brand-new plug’s life fast and often shows up as a return trip to the same cylinder within weeks of the plug swap being finished.
Pro Tips
Quick Buying Checklist
Confirm your engine first — M273 and M278 plugs are not interchangeable.
Check the gap on all eight plugs, even pre-gapped ones — shipping can bend the electrode.
Buy a full set of eight for a V8 — a partial swap leaves half the cylinders on old plugs.
Torque to 25 Nm (M273) or 23 Nm (M278) — never guess by feel in the aluminum head.
Inspect ignition coils while they’re off — a weak coil kills a new plug fast.
Common Mistakes Buyers Make
- Ordering a plug for the wrong GL450 generation. The M273 and M278 use different heat ranges entirely, so always confirm your engine code before buying, not just the model year — a few years fall right at the generation switch, and going by the calendar alone isn’t reliable.
- Buying only four plugs for a V8. The GL450 needs eight, and a partial set leaves half the cylinders running on worn electrodes until the next service, undoing most of the benefit of the swap and often triggering a lopsided idle.
- Skipping the gap check. A dropped box during shipping can close the gap on a fine-wire plug, and a two-minute feeler gauge pass on all eight catches it before it causes a misfire on the one cylinder you didn’t check twice.
- Using a standard deep socket instead of a spark plug socket. The rubber grommet inside protects the ceramic insulator, and metal-on-ceramic contact cracks the plug almost every time, usually on the last one you install when you’re rushing to finish.
- Ignoring ignition coil condition. Old coils cause new plugs to misfire early, so if your GL450 has high mileage, replace all eight coils alongside the plugs rather than one at a time as they fail over the following year.
Related Guides
Other Mercedes Spark Plug Guides
GL450 uses the M273 V8 — a much larger plug and coil pack than the C-Class 4-cyl/V6.
Also On CarAssists
More Guides for This Vehicle
Frequently Asked Questions
What spark plugs does a Mercedes GL450 use?
It depends on the generation. The 2007–2012 X164 with the naturally aspirated M273 V8 uses an NGK 4298 LFR6AIX-11 Laser Iridium plug or equivalent. The 2013–2019 X166 with the twin-turbo M278 V8 uses an NGK 95822 SILZKFR8D7S Laser Iridium plug. Confirm your engine badge before ordering, since the two are not interchangeable and use different gaps.
How many spark plugs does a GL450 V8 need?
Eight. Every GL450, whether the naturally aspirated M273 or the twin-turbo M278, is a V8 with one plug per cylinder. Many Amazon listings sell iridium plugs in boxes of four, so you’ll typically need to order two boxes to cover the full engine in a single maintenance session — factor that into your total budget before checkout.
How often should I change spark plugs in a GL450?
Mercedes recommends replacement every 60,000 miles or four years for both the M273 and M278 engines. Iridium plugs often reach 80,000 miles safely under normal driving. Towing, frequent short trips, or a hot climate can accelerate wear, so check sooner if you notice hesitation, a rough idle, or a stored misfire code.
Are aftermarket spark plugs safe for a Mercedes GL450?
Yes. Plugs from NGK, Bosch, and Denso that match the OE heat range, gap, and thread reach are safe and, in NGK’s case, are the same parts Mercedes uses as a factory supplier. As long as the specification matches your specific engine, an aftermarket plug performs identically to the dealer part at a lower cost.
Will changing my own spark plugs void the warranty?
No. Consumer protection law allows you to perform your own maintenance without voiding a factory warranty. Keep your receipts and a simple maintenance log, and use parts that meet the manufacturer’s specification so there’s no dispute if a claim ever comes up down the road.
Is it difficult to change spark plugs on a GL450?
It’s a moderate DIY job, not a beginner one. The engine cover and all eight ignition coils need to come off, and on the twin-turbo X166 some intake plumbing may need to shift for rear-cylinder access. Budget two to three hours with a thin-wall spark plug socket, extensions, and a torque wrench.
Do I need to disconnect the battery before changing spark plugs?
It’s a good safety habit. Disconnecting the negative terminal prevents accidental shorts while you’re handling eight sets of ignition coils, and it resets engine adaptations so the ECU can relearn idle behavior once the new plugs are installed and everything is buttoned back up.
Can I use one-step-colder spark plugs in a tuned GL450?
Only if your tuner specifically recommends it. A colder plug can help resist knock under higher boost on a modified M278, but on a stock engine it usually just causes fouling and a rougher cold start. Stick with the factory heat range unless a tune calls for otherwise, and confirm the recommendation in writing from your tuner.
Final Verdict
Our Top Recommendations for 2026
Match your plug to your GL450’s generation first — the M273 and M278 are not interchangeable, and that single decision matters more than any brand debate. The NGK options remain the safest factory-matched choice for either engine, while the Bosch 7411 covers the M273 for less if you’re budgeting for a full set of eight. Torque every plug to spec, check the gap before you start, and inspect the ignition coils while you have easy access to all eight.
