Mercedes-Benz AMG SL 55
The M177 is AMG's most widely used V8 biturbo today and is considered technically mature and long-lived. The hot-V turbocharger arrangement delivers spontaneous response with barely perceptible lag. Weaknesses are manageable: wastegate rattle in cold weather, ignition coil recall for early 2015 model years, valve cover gaskets with age. Regular oil changes with attention to oil quality deliver a very robust engine. In direct comparison with the M156 less emotional, but significantly more reliable and efficient.
476 hp open-air V8 — GT character for relaxed drivers
The SL55 is the more relaxed entry into the R232 world. 476 hp suffice for composed cruising, the V8 sounds more present with the fabric roof open than expected. Active rear-wheel steering makes the nearly 2 tonnes feel lighter. No more Vario hard-top like the R230 — soft-top only, but 60 kg lighter. Wind noise at higher speeds, electronics issues on early examples. For those who want V8 open-top without the radicalism of the SL63.
Engine Weaknesses 8
The MCT Speedshift gearbox (wet launch clutch instead of torque converter) wears the clutch significantly faster in frequent stop-and-go. Clutch replacement requires gearbox removal.
Symptoms: Judder on pull-away, clutch slip at full load, gearbox warning message, delayed engagement from standstill
Identical issue to the M176/M278: the solenoid leaks, oil migrates by capillary action through the wiring harness. On AMG vehicles this is even more frequent due to higher oil temperatures.
Symptoms: Cold-start rattle, camshaft adjuster fault code, oil traces on connector, potential ECU consequential damage
The camshaft cover gaskets on the M177 AMG V8 become brittle from the high heat exposure in the hot-V. Oil escapes onto turbochargers and exhaust system.
Symptoms: Oil smell on hot engine, oil film on turbochargers, smoke from engine bay
The M177 has several electric auxiliary coolant pumps for charge air cooling. These fail and lead to elevated charge air temperatures with power reduction.
Symptoms: Power reduction during spirited driving, cooling system fault codes, elevated charge air temperature
The camshaft adjuster solenoids on the M177 can leak internally or stick. Fault codes for camshaft position and rough running are the result.
Symptoms: Check engine light, rough idle, camshaft position fault codes, power loss in the lower rev range
Vehicles with M177/M178 engines built between Jan. and Nov. 2015 had faulty ignition coils that caused misfires. Mercedes replaced affected parts under a recall.
Symptoms: Rough idle, misfires, check engine light, occasional limp mode
The wastegate flaps of the BiTurbo system clatter briefly after cold start. Normally disappears after a few seconds. With prolonged operation replace the wastegate actuator.
Symptoms: Metallic clattering directly after cold start, disappears after warm-up, permanent with wear
As a direct-injection engine without port injection, carbon residues build up on the intake valves. Walnut blasting every 50,000–80,000 km recommended. Performance loss is gradual.
Symptoms: Gradually roughening idle, slight power loss, elevated fuel consumption
Vehicle Weaknesses 6
On the R232 with V8 engine, the starter-generator wiring harness can be damaged by friction against the driveshaft. Fire risk and drive loss. 12,341 vehicles affected.
The roof frame trim above the windscreen was not adequately secured on 795 vehicles and could detach while driving -- risk of accident.
On 795 vehicles worldwide, the roof frame trim above the windscreen was not adequately secured. The trim could detach while driving and endanger other road users.
The R232 draws excessive quiescent current through permanent internet connections. After just a few days standing, the 12V battery is too weak to start.
Jerky downshifts into lower gears at low speeds have been reported on the R232. Software updates as a remedy.
The 12V battery of the R232 discharges completely after just a few days standing. The cause is high quiescent current draw from always-on systems. Mercedes proposed retrofitting a CTEK charger in the boot.
Reports & Tests
9 owner complaints filed with NHTSA (2021–2025). Most reported: Electrical (5), Engine (4), Lane Departure (1).