BMW 728i
The 193 hp straight-six is the flagship of the M52 family — silky smooth, linearly building, with a throaty note from 4,000 rpm that crescendos into a full naturally-aspirated peak at 6,500 rpm. Compared to the 2.5L, the larger stroke is immediately felt: more torque from low down, less need to change gear. The engine is considered very long-lived provided the early Nikasil production (before model year 1999) and high-sulphur fuel legacy are avoided — from 1999 BMW switched to grey cast iron liners, which solved the problem. Check for Nikasil damage: compression and leak-down test before purchase. The DISA valve (intake noise, power loss around 60,000–120,000 km) and VANOS solenoid (cold-start hesitation) are typical cost items but well manageable.
Best inline-six
Silky naturally aspirated R6 — free-revving and refined.
Engine Weaknesses 5
The original M52B28 water pump has a plastic impeller that can break without warning. The result is immediate coolant failure and overheating. The M52 aluminium block is very sensitive to overheating.
Symptoms: Temperature gauge suddenly enters the red zone, coolant loss, engine runs hot without warning
Early M52B28 engines (up to March 1998) have Nikasil-coated cylinders. Sulphur in the fuel attacks the coating and causes cylinder bore out-of-roundness. Steel liners were introduced from 03/1998.
Symptoms: Rough idle, power loss, sharply increased oil consumption, cold-start difficulties, abnormal compression leak-down test result
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.
The single-VANOS on the M52B28 suffers from ageing sealing rings and can exhibit solenoid valve failures. Diagnostic values show deviations between target and actual. Rebuilt units are available.
Symptoms: Judder and power loss in the 1,500–2,000 rpm range, irregular idle, increased fuel consumption
The rectangular gasket between the oil filter housing and the engine block fails regularly. BMW part number 11421719855 — aftermarket gaskets tend to have a shorter service life.
Symptoms: Oil seeping from the side of the engine below the oil filter, oil smell when engine is hot, oil spots under the vehicle.
Vehicle Weaknesses 7
Sills and wheel arches rust heavily, especially on older examples. Fuel tank tray and brake lines under the floor are also at risk.
The plastic upper coolant hose fitting on the radiator breaks due to material fatigue at high operating temperatures.
Early production vehicles (1994–1996) have a manufacturing defect: cables in the front right wing chafe against the body. BMW marked repaired vehicles with a red dot.
Rear trailing arm bushings wear out. BMW only sells the complete arm. Polybushings as an alternative.
The crankcase ventilation membrane becomes porous and leads to heavy oil consumption. V8 engines M60/M62 affected.
Electric auxiliary water pump for the heater fails — insufficient heat at low revs.
Handbrake fails MOT at above-average rates per TÃœV report. Brake discs show heavy wear from 7 years.
Reports & Tests
64 owner complaints filed with NHTSA (1994–2001). Most reported: Engine & Cooling (15), Electrical (10), Airbags (8).