BMW 320d E90

The N47 engine (2007-2011 models) has the timing chain mounted at the rear of the engine, between the engine and gearbox. The chain tensioner bleeds oil pressure overnight, allowing the chain to slap on cold start. Cars built between March 2007 and January 2009 are most severely affected, though the issue persisted until approximately mid-2010 when BMW revised the tensioner and crankshaft sprocket. A distinctive rattling noise lasting 1-30 seconds on cold start is the earliest warning sign. If ignored, the chain can skip teeth and cause catastrophic valve-to-piston contact, destroying the engine. Replacement requires significant disassembly (engine removal on some configurations) and costs €1,500-2,500 at an independent specialist or €2,500-3,500 at a BMW dealer. Frequent oil changes (every 10,000 km maximum, using quality oil) are the best preventive measure. The earlier M47TU2 engine (2005-2007) uses a conventional front-mounted timing chain and is not affected by this issue.

Both the M47TU2 and N47 engines have swirl flaps in the intake manifold. On the M47TU2 (163 hp), these are 22mm flaps that can work loose from vibration and carbon buildup. If a flap detaches and enters the combustion chamber, it causes catastrophic piston, valve, and potentially turbo damage costing €4,000+. The N47 has an updated design that is somewhat less prone to catastrophic fracture, but the flaps still seize from carbon deposits, causing rough idle, power loss, and fault codes. Preventive removal and blanking with plates costs €150-300 and is strongly recommended, particularly on the M47TU2. On the N47, the flap actuator motor can also fail, causing noise and limp mode. Actuator replacement costs €200-400. Many knowledgeable owners have already performed the swirl flap delete.

The variable geometry turbocharger uses an electronic actuator that commonly fails on E90 320d models, particularly those built between 2005 and 2010. When the actuator sticks or fails, the turbo cannot regulate boost pressure correctly, resulting in intermittent power loss (the engine feels as though it has lost half its output) and limp mode. BMW does not sell the actuator separately from the turbocharger assembly. A specialist repair of the actuator alone costs €500-800. If the turbo internals are also damaged from running with a faulty actuator, full turbo replacement costs €1,200-1,800 including labor. Aftermarket remanufactured actuators are available for €200-350. Regular driving at varied engine loads and avoiding extended idle periods helps keep the actuator moving freely. On the M47TU2, oil starvation from a clogged crankcase ventilation valve is a common contributing factor to turbo failure.

Both the M47TU2 and N47 engines are equipped with a DPF that requires regular extended drives at highway speeds for passive regeneration. A failed or stuck-open thermostat is a common underlying cause on the E90, preventing the engine from reaching the 75+ degree coolant temperature needed to trigger regeneration. Cars driven predominantly on short urban trips accumulate soot faster than the DPF can burn it off. Symptoms include the DPF warning light, reduced power, and eventually limp mode. A forced regeneration at a workshop costs €150-300. Professional DPF cleaning runs €300-500. If the filter is beyond cleaning, replacement costs €1,200-2,000 including labor at a BMW dealer, or €800-1,500 at an independent specialist. Checking and replacing the thermostat (€200-350) is often the first step before addressing the DPF itself.

The EGR valve accumulates carbon and soot deposits over time, particularly on cars driven mainly in city traffic. Symptoms include rough idle, slight hesitation under acceleration, increased fuel consumption, and engine management warning light. The N47 engine is additionally subject to an EGR cooler recall for potential internal leaks that can cause fire risk. Cleaning the EGR valve at a workshop costs €150-250. If the valve needs full replacement, expect €400-600 at an independent shop or €600-800 at a BMW dealer. On the N47, the EGR cooler recall should be verified as completed before purchase. Regular highway driving helps keep the EGR system cleaner.

Oil leaks are among the most common issues on the E90 320d, particularly on cars over 10 years old. The valve cover gasket, oil filter housing gasket, and oil pan gasket all deteriorate from repeated heat cycling. The valve cover gasket typically starts weeping between 80,000-130,000 km, with oil dripping onto the exhaust and producing a burning smell. The oil filter housing gasket can also leak coolant since it incorporates a heat exchanger. Valve cover gasket replacement costs €300-500 at an independent shop, while the oil filter housing gasket adds €200-400. Addressing both during one service visit saves significant labor cost. The oil pan gasket is less common but more expensive due to access requirements (€300-500 additional).

The crankcase ventilation system on both the M47TU2 and N47 clogs over time, typically between 100,000-180,000 km. When the CCV valve fails, crankcase pressure builds up, pushing oil past seals and gaskets. This causes oil leaks, increased oil consumption, white smoke from the exhaust, and accelerates turbo seal wear. On the M47TU2, a clogged CCV is a primary contributor to turbo failure. The CCV valve and hose kit costs €80-150 for parts, with labor adding €100-250. This is considered essential preventive maintenance. Upgraded silicone hoses are available and offer significantly longer service life than the original rubber components.

The N47 engine's high-pressure fuel pump can fail due to internal wear, contamination from skipped fuel filter changes, or reduced lubricity in modern ultra-low sulfur diesel. When the pump fails catastrophically, metal debris can contaminate the entire fuel system including injectors, fuel rail, and lines, turning a €600-800 pump replacement into a €2,000-2,500+ fuel system overhaul. Symptoms include difficult starting, engine surging, and fluctuating idle speed. Regular fuel filter replacement (every 20,000-30,000 km) is the most effective preventive measure. This issue is less common than the timing chain problem but more expensive when it occurs due to secondary contamination damage.

The glow plug controller mounted under the intake manifold is exposed to significant heat and can fail, preventing one or more glow plugs from functioning correctly. Symptoms include extended cranking in cold weather, rough idle when cold, and incomplete DPF regeneration leading to secondary DPF issues. The controller itself costs €40-100. Individual glow plugs are €20-40 each. The main expense is labor, as the controller is located under the intake manifold and is difficult to access. Total replacement cost including plugs and controller runs €150-400 at an independent shop. It is recommended to replace both the controller and all four glow plugs at the same time.