Smart fortwo 0.6 W450

Smart has always had a problem with cracking turbo exhaust manifolds on the 450. The 600cc turbo tends to crack on the outside of the manifold. Symptoms include loss of turbo pressure, engine surging or pulsing during normal driving, and escaping waste gases that confuse the lambda sensors (causing rough running and higher fuel consumption). The manifold cracking is fundamentally a design weakness caused by thermal stress from the turbo's heat cycles. Smart attempted to address this on later 700cc models by using a thicker manifold casting, but this only delayed the problem. On the 600cc, manifold cracking has been documented as early as 50,000 km, with a second crack sometimes reappearing on replacement parts at similar intervals. A replacement turbo/manifold assembly costs approximately €600 for parts, plus 3-4 hours labor. Independent Smart specialists can often source refurbished units for less. Total repair typically runs €500-1,200 depending on whether just the manifold or the entire turbo assembly needs replacing.

The 599cc M160 engine is a small, highly stressed turbocharged unit with known piston ring longevity issues. Owners commonly report oil consumption of 1 litre per 1,000 km or worse developing between 70,000-100,000 km. The problem begins when piston oil rings gum up with carbon deposits, particularly if the wrong oil specification was used or oil changes were neglected. Cylinder 1 and 3 are the most commonly affected. Once the rings are stuck, compression drops and the engine begins burning oil past the pistons. Early signs include blue exhaust smoke on deceleration and steadily increasing oil consumption. A crankcase breather valve blocked with dry carbon deposits can accelerate the problem. If caught early, a breather valve clean or replacement (under €50) may temporarily slow the consumption. However, most cases eventually require an engine rebuild (new piston rings, big-end shells, timing chain guide) costing €800-1,500 at an independent specialist, or a reconditioned engine exchange for approximately €900 plus fitting. Evilution, the primary Smart technical resource, places the average reconditioning point at approximately 100,000 km for the 600cc engine.

The six-speed Softip automated manual gearbox uses a clutch actuator to operate the single dry clutch. The actuator's internal mechanism is susceptible to dried-out factory grease and wear. Symptoms start as increasingly slow or jerky gear changes and can progress to complete inability to engage gears or loss of drive. Cars that have sat idle for extended periods are particularly susceptible, as the actuator can seize from inactivity. Before replacing the actuator, lubricating the internal mechanism can sometimes restore function temporarily. A genuine Smart actuator costs €600-800 at a Mercedes dealer including coding. Independent specialists and remanufacturers offer repaired units from €250-500 fitted, often with no re-coding required. This is one of the most common repairs on any W450, typically occurring between 50,000-100,000 km.

The Signal Acquisition Module (SAM unit) is the main electrical control centre of the W450. It manages all lighting, central locking, wipers, heater, and communicates with the engine ECU. Over time, the solder joints on the circuit board crack from engine vibration, causing a wide range of intermittent electrical problems. Symptoms include randomly illuminating warning lights, intermittent failure of windows/heating/central locking, no-start conditions, and hazard lights that stop working. Water ingress from leaking door seals or improperly sealed grommets can accelerate corrosion on the SAM board. A new SAM unit from Mercedes costs €400-600 plus coding to the vehicle's immobiliser. However, most SAM failures can be repaired by re-soldering the cracked joints, which an electronics specialist can do for €100-250. This is a well-documented repair with high success rates.

The W450's tridion safety cell came from the factory with a thin wax coating for rust protection. Rock chips break through this layer, and corrosion develops underneath. Common rust areas include the rear wheel arch (behind the liner, hidden from casual inspection), the inner sills, the rear X-frame subframe, and the door sill areas above the plastic mouldings where dirt traps moisture. The rear wishbones can also corrode significantly. Surface rust on the tridion is mostly cosmetic and can be treated, but structural corrosion of the subframe or inner sills can make the car uneconomical to repair. Repair costs range from €200 for localised rust treatment to €800-1,200 for welding repairs on structural areas. Cars from northern European climates with salted roads are at highest risk. The first indication is usually paint bubbling or failing an inspection when something corroded is discovered behind the arch liner.

The turbo wastegate controls exhaust gas bypass to regulate boost pressure. The wastegate arm connector can seize from carbon buildup and corrosion, particularly on cars driven gently in the city without regular hard acceleration to keep the mechanism free. Symptoms include a rattling noise at certain RPM ranges, severe loss of power, engine management light, and limp mode. In mild cases, freeing and lubricating the wastegate arm can resolve the issue for €100-200. If the internal wastegate mechanism has failed, turbo replacement may be needed at €600-900. This overlaps with turbo manifold issues and both are often addressed together.

The W450's rubber engine mounts deteriorate from heat cycling and the turbo engine's vibration. When the mounts fail, the engine moves excessively, producing vibration at idle and noticeable clunking during gear changes or acceleration. OEM replacement mounts cost €30-50 each, with labor running approximately one hour. Polyurethane aftermarket options (Powerflex) are available for improved durability at €80-120. Most owners encounter this between 60,000-100,000 km, and it is often treated as a routine renewal rather than a surprise failure.

The W450 has several common leak points. The rear quarter windows are frequently the source of mysterious dampness in the boot area, with water seeping between the glass and the rubber seal. Door seals harden and crack over time, particularly on the driver's side from frequent use. The interior mirror trim screws on the windscreen header rail often lack adhesive patches, allowing water to run down the front edge of the door frame and under the carpet. Additionally, a large wiring grommet through the bulkhead can allow water into the cabin if it has shifted or deteriorated. Replacing door seals costs €50-150, rear window re-sealing with silicone is a simple DIY job, and sorting all leak points on a typical W450 rarely exceeds €400. However, prolonged dampness can cause floor corrosion and electrical faults through water reaching the SAM unit.