Smart fortwo 0.7 W450

This is a well-documented design weakness across all W450 turbo engines. The turbo exhaust manifold develops cracks from repeated heating and cooling cycles. On the 698cc engine, the manifold was redesigned to be thicker than the 599cc version, but this only delayed rather than prevented cracking. Symptoms include loss of boost pressure, engine surging at steady throttle, increased exhaust noise, and the lambda sensors producing erratic readings. The crack can be external (visible) or internal near the wastegate and impeller. In severe cases the manifold can fracture into pieces. Aftermarket replacement manifolds cost €200-400, with labor adding €200-400. A full turbo-plus-manifold replacement runs €800-1,500 if the turbo itself has been damaged by escaping exhaust gases. Some owners have had the manifold welded as a temporary repair for €100-200, but cracks tend to return. This issue affects virtually every W450 turbo engine eventually, typically appearing between 60,000 and 120,000 km.

The 698cc M160 turbo engine has a limited design lifespan. Piston ring wear and valve guide seal deterioration are common, causing progressively increasing oil consumption. Smart/Mercedes defines excessive consumption as 1 litre per 1,000 km, but many W450s exceed this well before reaching 120,000 km. Symptoms begin with blue smoke on cold starts (valve guides) and progress to constant smoking and power loss (rings). The middle cylinder tends to suffer first. Engine reconditioning (new rings, guides, valve seats) typically costs €1,500-2,000 at a specialist. A complete used replacement engine runs €800-1,500 plus fitting. The Brabus variant with an oil cooler lasted notably longer (up to 200,000 km), suggesting thermal management plays a role in premature wear. Regular oil changes with quality synthetic oil every 10,000 km or annually are essential to maximise engine life.

The 6-speed Softtouch automated manual gearbox uses a clutch actuator that converts rotational movement into the linear force needed to operate the clutch. Internal worm gears and spiral shafts wear prematurely, particularly when the factory grease dries out. Symptoms include increasingly jerky gear changes, inability to select specific gears (especially reverse), kangarooing from standstill, and dashboard gear warnings. Specialist repair services receive W450 actuators for repair daily, indicating how widespread the problem is. A new clutch actuator from a Smart parts supplier costs around €400, while specialist rebuilds are available from €200-350 plus fitting. Full dealer replacement with coding can run €800-1,200. The issue typically appears between 50,000 and 100,000 km, though city driving with constant stop-start accelerates wear.

The Signal Acquisition Module (SAM unit) is the central fuse box and relay board. Over time, solder joints crack from vibration and thermal cycling, causing a wide range of intermittent electrical symptoms: no-start conditions, hazard lights malfunctioning, heater stopping, electric windows becoming intermittent, dashboard warning lights illuminating randomly, and fuel pump relay failures. Water ingress into the SAM unit housing is also documented. The unit can partially fail, affecting only certain circuits. Re-soldering the affected joints at an electronics specialist costs €100-200. A professional SAM unit repair service charges around €650 (send-in service with 48-hour turnaround). Replacement with a used unit plus coding runs €200-400. Cars older than 10-12 years are most susceptible.

The W450 left the factory with minimal underbody protection. The tridion safety cell itself has reasonable powder-coat protection, but the engine subframe, front steering knuckles, rear wishbones, and steel bumper reinforcements corrode aggressively. The rear wheel arch area around liner fixing screws is particularly vulnerable, where rusting steel inserts can expand and crack the surrounding plastic body panels. The rear crash bar is another notorious rust spot. Surface rust is cosmetic, but structural corrosion of load-bearing components can make the car uneconomical to repair. In northern European climates with salted roads, significant corrosion is common on cars older than 12-15 years. Welding repairs to the subframe typically cost €300-800, with full subframe replacement running €800-1,200 including labor.

The window regulator mechanism in the W450 uses a cable-and-spool system with plastic clips that deteriorate over time. The cable can loosen on the spool and loop over itself, effectively shortening it and preventing full window travel. Plastic mounting clips also crack. Symptoms include windows that stop halfway, move unevenly, make grinding or clicking noises, or drop down inside the door. Repair kits (new cables and clips) are widely available for €30-60, making DIY repair feasible. A full regulator replacement costs €80-150 for the part plus €50-100 labor. The issue is common enough that dedicated repair guides and video tutorials exist for the W450 specifically.