Mercedes-Benz SLK R170
Weaknesses, engine ratings and buying advice
Generations
Engine Overview
The Mercedes-Benz SLK R170 is available with 5 engine variants — from 121 to 354 hp.
Proven four-cylinder with optional supercharger. Robust and long-lived; the supercharged variant has good torque. Supercharger magnetic clutch can wear.
- !! Head Gasket Ages and Leaks from 120,000 km
One of the most common weak points of the M111: the head gasket becomes porous and starts leaking between 75,000 and 150,000 km. Typical for older M111 engines.
Symptoms: Coolant loss without visible leak, white exhaust plume, oil-coolant emulsion, engine overheats - !! Supercharger Magnetic Clutch Fails from 100,000 km
The supercharger magnetic clutch and the K40 relay are weak points on the M111 Kompressor. The clutch no longer engages, supercharger boost is absent. K40 relay is often repairable at low cost.
Symptoms: Sudden power loss from approx. 3,000 rpm, supercharger cuts in sporadically or not at all - !! Ignition Coils Wear Out Due to Neglected Spark Plugs from 80,000 km
If spark plugs are left too long in the M111, the voltage load on the ignition coils increases substantially. Always replace ignition coil and spark plug together.
Symptoms: Stumbling under load, engine misfires, ignition failure in individual cylinders, CEL, rough idle
+ 3 more engine weaknesses + vehicle weaknesses
Proven four-cylinder with optional supercharger. Robust and long-lived; the supercharged variant has good torque. Supercharger magnetic clutch can wear.
- !! Head Gasket Ages and Leaks from 120,000 km
One of the most common weak points of the M111: the head gasket becomes porous and starts leaking between 75,000 and 150,000 km. Typical for older M111 engines.
Symptoms: Coolant loss without visible leak, white exhaust plume, oil-coolant emulsion, engine overheats - !! Supercharger Magnetic Clutch Fails from 100,000 km
The supercharger magnetic clutch and the K40 relay are weak points on the M111 Kompressor. The clutch no longer engages, supercharger boost is absent. K40 relay is often repairable at low cost.
Symptoms: Sudden power loss from approx. 3,000 rpm, supercharger cuts in sporadically or not at all - !! Ignition Coils Wear Out Due to Neglected Spark Plugs from 80,000 km
If spark plugs are left too long in the M111, the voltage load on the ignition coils increases substantially. Always replace ignition coil and spark plug together.
Symptoms: Stumbling under load, engine misfires, ignition failure in individual cylinders, CEL, rough idle
+ 3 more engine weaknesses + vehicle weaknesses
Proven four-cylinder with optional supercharger. Robust and long-lived; the supercharged variant has good torque. Supercharger magnetic clutch can wear.
- !! Head Gasket Ages and Leaks from 120,000 km
One of the most common weak points of the M111: the head gasket becomes porous and starts leaking between 75,000 and 150,000 km. Typical for older M111 engines.
Symptoms: Coolant loss without visible leak, white exhaust plume, oil-coolant emulsion, engine overheats - !! Supercharger Magnetic Clutch Fails from 100,000 km
The supercharger magnetic clutch and the K40 relay are weak points on the M111 Kompressor. The clutch no longer engages, supercharger boost is absent. K40 relay is often repairable at low cost.
Symptoms: Sudden power loss from approx. 3,000 rpm, supercharger cuts in sporadically or not at all - !! Ignition Coils Wear Out Due to Neglected Spark Plugs from 80,000 km
If spark plugs are left too long in the M111, the voltage load on the ignition coils increases substantially. Always replace ignition coil and spark plug together.
Symptoms: Stumbling under load, engine misfires, ignition failure in individual cylinders, CEL, rough idle
+ 3 more engine weaknesses + vehicle weaknesses
Three-valve V6 with individual ignition coils. Smooth and strong. Typical weak points: crankcase breather and intake manifold flaps. High mileages achievable.
- !! Camshaft Adjuster Leaks Oil into Wiring Harness from 130,000 km
The camshaft adjuster solenoid on the M112 develops a leak and draws oil by capillary action into the wiring harness. Oil can migrate as far as the engine ECU and destroy it.
Symptoms: Cold-start rattling that disappears after 1–2 seconds, camshaft adjuster fault code, oil traces at wiring connector, later ECU faults - !! Intake Manifold Vacuum Hose Breaks from 120,000 km
The vacuum hose for the variable intake manifold on the M112 becomes brittle and breaks. The swirl flaps stick. The hose is not available individually — the entire intake manifold is needed.
Symptoms: Power drop, slight hesitation at part throttle, engine runs but without full power - !! Valve Cover Gasket and Front Cover Gasket Leaking from 130,000 km
On the M112 V6 the valve cover gaskets become porous over time. Especially the rubber seals on the front cover between the timing cover and engine block fail on virtually all high-mileage M112 engines.
Symptoms: Oil spots on the floor, oil smell after driving, oily engine bay, dropping oil level
+ 4 more engine weaknesses + vehicle weaknesses
Three-valve V6 with individual ignition coils. Smooth and strong. Typical weak points: crankcase breather and intake manifold flaps. High mileages achievable.
- !! Camshaft Adjuster Leaks Oil into Wiring Harness from 130,000 km
The camshaft adjuster solenoid on the M112 develops a leak and draws oil by capillary action into the wiring harness. Oil can migrate as far as the engine ECU and destroy it.
Symptoms: Cold-start rattling that disappears after 1–2 seconds, camshaft adjuster fault code, oil traces at wiring connector, later ECU faults - !! Intake Manifold Vacuum Hose Breaks from 120,000 km
The vacuum hose for the variable intake manifold on the M112 becomes brittle and breaks. The swirl flaps stick. The hose is not available individually — the entire intake manifold is needed.
Symptoms: Power drop, slight hesitation at part throttle, engine runs but without full power - !! Valve Cover Gasket and Front Cover Gasket Leaking from 130,000 km
On the M112 V6 the valve cover gaskets become porous over time. Especially the rubber seals on the front cover between the timing cover and engine block fail on virtually all high-mileage M112 engines.
Symptoms: Oil spots on the floor, oil smell after driving, oily engine bay, dropping oil level
+ 4 more engine weaknesses + vehicle weaknesses
Vehicle Weaknesses
| Weakness | Cost | |
|---|---|---|
| Vario roof hydraulics leaking Vario roof hydraulic cylinders develop leaks and the roof no longer opens or closes fully. Opening time over 28 seconds indicates hydraulic loss. Specialist repair required. Symptoms: Roof sticks, opening sequence takes over 28 seconds, hydraulic oil in boot from 100,000 km | Medium | |
| Roof hydraulic cylinders: O-rings and rod seals leaking O-rings and rod seals wear in temperature extremes, particularly in summer. Complete replacement at Mercedes over 8,000 EUR; seal kit repair significantly cheaper. Symptoms: Hydraulic oil escapes at rollover bars or boot lid. Roof opens progressively more slowly. System loses pressure. from 80,000 km | Medium | |
| Drain channels blocked: water in boot and interior The four water drainage channels block with leaves and dirt. The thin-walled original hoses kink at the pass-through point. Boot lid seal replacement approximately 500 EUR per side. Symptoms: Water in boot after rain. Misted windows. Wet carpet. When flushed, only a trickle instead of a jet. from 80,000 km | Medium | |
| Water ingress into doors and roof area Roof frame and door seals become porous; water enters the door cards. Damp interior encourages rust in the underbody. Seat squeaking and poor door closure are common. Symptoms: Wet door cards after rain, squeaking seats, mould smell in interior from 100,000 km | Low |
Test Reports
TÜV Report 2024
The SLK R170 shows age-appropriate defect rates in its later life, sitting in the mid-field of its age group.
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Explore more
All Mercedes-Benz models Known Problems and Issues +
A total of 22 weaknesses have been documented for the Mercedes-Benz SLK R170 (1996–2004) — 13 engine-related and 9 vehicle-related. Typical issues affect Body, Rust, Gearbox, Suspension.
SLK (M111, 1996–2000) — Be Careful: Head Gasket Ages and Leaks, Supercharger Magnetic Clutch Fails, Ignition Coils Wear Out Due to Neglected Spark Plugs. Power: 136 PS.
SLK (M111, 1996–2000) — Be Careful: Head Gasket Ages and Leaks, Supercharger Magnetic Clutch Fails, Ignition Coils Wear Out Due to Neglected Spark Plugs. Power: 192 PS.
SLK (M111, 1996–2000) — Be Careful: Head Gasket Ages and Leaks, Supercharger Magnetic Clutch Fails, Ignition Coils Wear Out Due to Neglected Spark Plugs. Power: 193–197 PS.
SLK (M111, 2000–2004) — Be Careful: Head Gasket Ages and Leaks, Supercharger Magnetic Clutch Fails, Ignition Coils Wear Out Due to Neglected Spark Plugs. Power: 163 PS.
SLK (M112, 2000–2004) — Be Careful: Camshaft Adjuster Leaks Oil into Wiring Harness, Intake Manifold Vacuum Hose Breaks, Valve Cover Gasket and Front Cover Gasket Leaking. Power: 218 PS.
SLK (M112, 2001–2004) — Be Careful: Camshaft Adjuster Leaks Oil into Wiring Harness, Intake Manifold Vacuum Hose Breaks, Valve Cover Gasket and Front Cover Gasket Leaking. Power: 354 PS.
What to watch out for with the Mercedes-Benz SLK? See the detailed listing of all engine and vehicle weaknesses in the sections above.
Frequently Asked Questions
What problems and weaknesses does the Mercedes-Benz SLK R170 have? +
What should I look for when buying a used Mercedes-Benz SLK R170? +
Which engine is recommended? +
Which Mercedes-Benz SLK R170 engine is the most fun? +
Is the Mercedes-Benz SLK R170 worth buying used? +
What horsepower variants are available for the Mercedes-Benz SLK R170? +
Last updated: February 2026 · All information without guarantee