BMW Z4 E85

The N46B20 is a two-litre four-cylinder with Valvetronic variable valve lift, producing between 129 and 150 hp as the successor to the M54B22. In daily use a pleasantly smooth and economical engine that eliminates the conventional throttle body through continuously variable valve lift. The most well-known weakness is the Valvetronic eccentric shaft — when its bearings wear, rattling and clattering noises appear, and the repair is involved, sometimes requiring cylinder head removal. Timing chain and tensioner should be inspected beyond 150,000 km; a stretched chain makes itself known through rattling on cold starts. The crankcase ventilation system is a known wear item that can cause oil leaks and rough idle when it fails. VANOS solenoid valves become contaminated with extended oil change intervals. When buying used, listen for clean idle and ask about oil consumption — more than 0.5 litres per 1,000 km is a warning sign. Overall a reliable engine when the known wear items are kept in check.

• !! Timing chain stretched / chain tensioner defective from 130,000 km

  The timing chain stretches prematurely due to a faulty chain tensioner. Plastic guide rails become brittle and break. Engine damage from chain jump is possible.

  Symptoms: Rattling or clattering on cold start in the first few seconds, which improves or worsens as the engine warms up.
  800–2,200 $
  Ad timing chain N46B20chain tensioner BMW 318i E46 E9011311742042
• !! Valvetronic eccentric shaft / actuator motor defective from 150,000 km

  The Valvetronic actuator motor or eccentric shaft fails at around 150,000 km. Fault code 2A67 is typical. The engine runs but without variable valve lift control — increased fuel consumption, limp mode.

  Symptoms: Judder at 2,000 rpm; rough cold start; increased fuel consumption; engine stumbling when pulling away; fault code 2A67
  400–1,200 $
  Ad N46 valvetronic actuator motorBMW 11377507804N46 Exzenterwelle
• ! VANOS solenoid valve defective from 100,000 km

  The VANOS solenoid valves wear and cause rpm fluctuations, power loss, and starting difficulties, especially at low revs.

  Symptoms: Rpm fluctuations at idle, power loss at low revs, occasional starting difficulties.
  150–500 $
  Ad VANOS solenoid valve N46VANOS solenoid valve BMW 318i 320i

+ 2 more engine weaknesses + vehicle weaknesses

The M54B22 is a 2.2-litre inline six with aluminium crankcase, double VANOS, and around 170 hp — the successor to the M52TUB25 with slightly reduced displacement but a more modern block. Like all M54 engines, it impresses with butter-smooth running and refined power delivery. The most common weakness is the cooling system: water pump, thermostat, and especially the plastic expansion tank become brittle over the years and can burst without warning — preventive replacement from 120,000 km or after eight years at the latest is recommended. The crankcase ventilation system is a known wear item whose failure manifests as oil mist under the bonnet, fluctuating idle, and increased oil consumption. VANOS seals are standard fare as with all M5x/M54 engines. Valve cover gasket and oil filter housing gasket should be checked from 150,000 km. The M54B22 is overall a frugal and durable engine that offers less torque than the M54B25 but is slightly more economical on fuel. Important when buying: check the entire cooling system and ask when water pump and thermostat were last replaced.

• !! DISA flap valve defective from 120,000 km

  The DISA flap in the M54B22 intake manifold can break its shaft. If the flap breaks off and enters the engine, catastrophic damage is likely. The membrane wears regularly. Preventive replacement from 120,000 km is advisable.

  Symptoms: Hesitation under acceleration, power loss, whistling noise after engine shutdown, rough idle
  100–300 $
  Ad DISA valve M54B22BMW 11611432802DISA valve E46 320i
• !! DISA valve defective from 120,000 km

  The DISA variable intake valve breaks at the shaft base or the membrane tears. Fragments can be sucked into the engine and cause catastrophic damage.

  Symptoms: Power loss in the lower rev range, rattling or clattering from the intake area, in the worst case engine damage from ingested fragments.
  130–400 $
  Ad DISA valve M54DISA repairkit BMW 520i
• !! Crankcase ventilation / air leak from 140,000 km

  The crankcase ventilation hoses and the accordion boot to the idle control valve become brittle and crack. Unmetered air bypasses the MAF sensor and overwhelms mixture control. Typical on vehicles over 10–15 years old.

  Symptoms: Rough idle, rich/lean mixture deviation, misfires, poor cold-start drivability, engine warning light
  80–300 $
  Ad KGE Schlauch M54B22Faltenbalg M54 E46BMW 11157531589crankcase ventilation M54

+ 2 more engine weaknesses + vehicle weaknesses

The M54B25 is a 2.5-litre inline six with aluminium crankcase and double VANOS, producing around 192 hp and widely regarded as the most popular engine of its model range. With good reason: it offers the perfect balance of refinement, sufficient power for every daily situation, and tolerable fuel consumption. The silky-smooth six-cylinder running is addictive and impressive even by modern standards. The Achilles heel is — as with all M54 engines — the cooling system. The plastic expansion tank becomes brittle after eight to ten years and can burst, leading to overheating that warps the cylinder head. Water pump and thermostat belong on the fixed maintenance schedule every 100,000 km. Crankcase ventilation is a known wear item that causes oil consumption and rough idle when it fails. VANOS seals should be checked first when idle fluctuations appear — an inexpensive repair kit usually solves the issue permanently. Valve cover gasket and oil filter housing gasket are due at high mileage. When buying, inspect the expansion tank — if it is still original, replacement is imminent. An engine that can be bought with confidence.

• !! DISA valve defective from 120,000 km

  The DISA variable intake valve breaks at the shaft base or the membrane tears. Fragments can be sucked into the engine and cause catastrophic damage.

  Symptoms: Power loss in the lower rev range, rattling or clattering from the intake area, in the worst case engine damage from ingested fragments.
  130–400 $
  Ad DISA valve M54B25DISA repairkit BMW 325i E46
• !! Electric thermostat defective from 100,000 km

  The Behr/Mahle electric coolant thermostat fails prematurely. Failure causes overheating or permanent cold running with increased fuel consumption.

  Symptoms: Engine does not reach operating temperature or overheats quickly, poor heater output.
  120–320 $
  Ad thermostat M54 original BMW E46thermostat E46 325i
• !! Crankcase ventilation — membrane tear from 130,000 km

  The plastic membrane in the crankcase ventilation system typically tears at 120,000–150,000 km. Result: air leaks, oil enters the intake tract, increased oil consumption and rough running.

  Symptoms: Rough idle; slight exhaust smoke; increased oil consumption; "puff" when opening the oil filler cap; air-leak fault codes
  80–250 $
  Ad M54 crankcase ventilationM54 CCVBMW E46 KGE Membran11617501566

+ 3 more engine weaknesses + vehicle weaknesses

The N52B25 is a 2.5-litre inline six with a magnesium-aluminium composite crankcase and Valvetronic, producing between 177 and 218 hp depending on the power level. One of the last great BMW naturally aspirated engines and for many enthusiasts the epitome of silky-smooth six-cylinder character. In daily use refined, eager to rev, and very durable with proper care. The most common weakness is the oil filter housing gasket, which hardens over time and causes oil leaks — a relatively inexpensive repair that should not be ignored. VANOS solenoid valves become contaminated with extended change intervals, causing rough idle and power loss. The crankcase ventilation system is designed as a wear item and should be replaced when symptoms like oil mist or fluctuating idle appear. Valve stem seals can harden at high mileage, leading to slight oil consumption. The magnesium crankcase is more sensitive to overheating than full aluminium — check the cooling system regularly for leaks. Overall an excellent engine that causes few worries when oil maintenance is kept up.

• !! Electric water pump defective from 100,000 km

  The N52 electric water pump is a known wear item. When it fails the engine overheats quickly. Recommended: preventive replacement when any abnormalities appear or from around 100,000 km.

  Symptoms: Coolant temperature gauge rises quickly, coolant loss, audible pump malfunction, engine overheating.
  400–900 $
  Ad water pump N52B25 elektrischcoolant pump BMW 325i E90 N52
• !! Eccentric shaft sensor (Valvetronic) failure from 80,000 km

  The eccentric shaft sensor on the N52B25 Valvetronic system fails sporadically. Fuel consumption jumps sharply by 30–35%; the sensor costs approximately €315 new from BMW.

  Symptoms: Sporadic eccentric shaft sensor fault code; fuel consumption jumps from ~10 to ~13.5 L/100 km; power loss; whistling noise under acceleration
  300–700 $
  Ad N52 ExzenterwellensensorBMW 11377524879Valvetronic sensor N52
• !! Oil filter housing gasket leaking — oil in coolant from 120,000 km

  The seals in the oil-coolant heat exchanger inside the oil filter housing become porous and allow oil into the coolant. Affects N52, N53, and N54 equally. Always replace both seals at the same time.

  Symptoms: Oil film on the coolant surface; oily-looking oil filler cap; no white smoke or visible fluid loss despite apparent head gasket symptoms
  200–600 $
  Ad N52 oil filter housing gasketBMW 11427509657oil filter housing gasket N52

+ 4 more engine weaknesses + vehicle weaknesses

The N52B25 is a 2.5-litre inline six with a magnesium-aluminium composite crankcase and Valvetronic, producing between 177 and 218 hp depending on the power level. One of the last great BMW naturally aspirated engines and for many enthusiasts the epitome of silky-smooth six-cylinder character. In daily use refined, eager to rev, and very durable with proper care. The most common weakness is the oil filter housing gasket, which hardens over time and causes oil leaks — a relatively inexpensive repair that should not be ignored. VANOS solenoid valves become contaminated with extended change intervals, causing rough idle and power loss. The crankcase ventilation system is designed as a wear item and should be replaced when symptoms like oil mist or fluctuating idle appear. Valve stem seals can harden at high mileage, leading to slight oil consumption. The magnesium crankcase is more sensitive to overheating than full aluminium — check the cooling system regularly for leaks. Overall an excellent engine that causes few worries when oil maintenance is kept up.

• !! Electric water pump defective from 100,000 km

  The N52 electric water pump is a known wear item. When it fails the engine overheats quickly. Recommended: preventive replacement when any abnormalities appear or from around 100,000 km.

  Symptoms: Coolant temperature gauge rises quickly, coolant loss, audible pump malfunction, engine overheating.
  400–900 $
  Ad water pump N52B25 elektrischcoolant pump BMW 325i E90 N52
• !! Eccentric shaft sensor (Valvetronic) failure from 80,000 km

  The eccentric shaft sensor on the N52B25 Valvetronic system fails sporadically. Fuel consumption jumps sharply by 30–35%; the sensor costs approximately €315 new from BMW.

  Symptoms: Sporadic eccentric shaft sensor fault code; fuel consumption jumps from ~10 to ~13.5 L/100 km; power loss; whistling noise under acceleration
  300–700 $
  Ad N52 ExzenterwellensensorBMW 11377524879Valvetronic sensor N52
• !! Oil filter housing gasket leaking — oil in coolant from 120,000 km

  The seals in the oil-coolant heat exchanger inside the oil filter housing become porous and allow oil into the coolant. Affects N52, N53, and N54 equally. Always replace both seals at the same time.

  Symptoms: Oil film on the coolant surface; oily-looking oil filler cap; no white smoke or visible fluid loss despite apparent head gasket symptoms
  200–600 $
  Ad N52 oil filter housing gasketBMW 11427509657oil filter housing gasket N52

+ 4 more engine weaknesses + vehicle weaknesses

The 231 hp naturally aspirated engine is the emotional highlight of the M54 family: a straight-six that pulls smoothly from low down and above 4,500 rpm blossoms into a sharp, throaty note that makes every rev step audible. Compared to the 2.5L it delivers noticeably more pull in the mid-range without losing the characteristic lightness of a naturally aspirated engine. Longevity is excellent — many examples exceed 300,000 km with careful maintenance. Weaknesses: double VANOS O-rings (cold rattle, 60,000–150,000 km), DISA valve (clunk on acceleration), crankcase ventilation (CCV membrane, oil consumption). Cooling care is important: replace plastic thermostat housing and coolant temperature sensor in good time. Buying tip: measure oil consumption — more than 0.5 litres per 1,000 km suggests worn piston rings.

• !! DISA valve defective from 100,000 km

  The DISA variable intake valve breaks at the shaft base or the membrane tears. Fragments can be sucked into the engine and cause catastrophic damage.

  Symptoms: Power loss in the lower rev range, rattling or clattering from the intake area, in the worst case engine damage from ingested fragments.
  130–400 $
  Ad DISA valve M54B30DISA repairkit BMW 330i 530i
• !! Double-VANOS O-rings worn from 100,000 km

  The O-rings in the double-VANOS system harden and lose their sealing effect. Oil pressure drops and variable valve timing becomes imprecise.

  Symptoms: Rough idle, power loss especially in the lower rev range, occasional rattling on cold start.
  200–600 $
  Ad Doppel-VANOS seal kit M54VANOS O-Ringe E46 330i
• !! Piston rings coked — high oil consumption from 120,000 km

  Carbon deposits in the piston ring grooves can cause the oil scraper rings to lose their function. The M54B30 then burns up to 1 litre per 700 km, which BMW internally tolerated as borderline acceptable.

  Symptoms: Dipstick check needed at every fuel stop; slight blue smoke under load; spark plugs show oil deposits; smell of burning oil
  800–3,500 $
  Ad M54B30 piston ringsBMW E46 330i piston ringtauschM54 oil control ring

+ 3 more engine weaknesses + vehicle weaknesses

The 258 hp top version of the N52 is one of the last large high-revving naturally aspirated engines from BMW: a magnesium-aluminium composite block that defines the class through extreme smoothness and a willingness to rev that drivers describe as 'like a sewing machine' — so even and effortless in its climb. Compared to the N54 turbo it sounds cleaner and more natural, without turbo hiss; instead a clear naturally aspirated note that fills out with increasing revs. Cold-start behaviour is impeccable; in daily use it runs nearly maintenance-free. Typical weaknesses: electric water pump (fails without warning, 80,000–150,000 km, preventive replacement recommended), Valvetronic eccentric shaft sensor (fault code, limp mode), VANOS solenoids with sludge build-up. Buying tip: check service history, as missed oil changes can permanently impair VANOS function.

• !! Electric water pump defective from 100,000 km

  The N52 electric water pump is a known wear item. When it fails the engine overheats quickly. Recommended: preventive replacement when any abnormalities appear or from around 100,000 km.

  Symptoms: Coolant temperature gauge rises quickly, coolant loss, audible pump malfunction, engine overheating.
  400–900 $
  Ad water pump N52B30 elektrischcoolant pump BMW 330i E90 N52Elektrische water pump 11517632426thermostat 11537549476
• !! Oil filter housing gasket — oil into coolant from 120,000 km

  The gasket between the oil filter housing and the engine block ages and becomes porous, allowing oil into the coolant. Symptoms resemble a head gasket failure. Early replacement of both seals is recommended.

  Symptoms: Oil film on the coolant; discoloured oil filler cap; coolant slightly foamy or brownish; no white exhaust smoke — a key differentiator from head gasket damage
  150–400 $
  Ad N52 oil filter housing gasketN52 oil filter housing gasketBMW N52 Ölwärmetauscher gasketoil separator 11617531423
• !! Eccentric shaft sensor (Valvetronic) failure from 100,000 km

  The Valvetronic eccentric shaft sensor fails due to moisture and ageing. Fault code 2A31 is typical. The sensor costs approximately €275; installation requires opening the cam cover.

  Symptoms: Rough idle; severe judder with light throttle input; increased fuel consumption (up to +30%); fault code 2A31; engine runs better with the sensor disconnected
  300–700 $
  Ad N52 ExzenterwellensensorN52B30 Exzenterwellen-sensor 11377527016BMW Valvetronic sensor 2A31

+ 2 more engine weaknesses + vehicle weaknesses