The E38 750iL with the M73 5.4L V12 is a technological marvel that becomes a maintenance nightmare after 100k miles. The engine is prone to catastrophic failures from Nikasil bore wear and cooling system neglect, while the transmission, suspension, and electronics demand constant attention and deep pockets.
Nikasil Cylinder Bore Failure (Pre-9/98 Production)
Common · high severityTypical onset: 80,000-130,000 mi
Symptoms: excessive oil consumption (1qt per 500-800 miles), cold-start smoking and rough idle, loss of compression in multiple cylinders, check engine light with misfire codes
Fix: Early M73 engines used Nikasil cylinder liners that deteriorate from sulfur in US fuel. Only fix is complete engine rebuild with Alusil block replacement or sleeved cylinders. 60-80 labor hours for removal, rebuild, and reinstallation. Many owners opt for used Alusil engine swaps from post-9/98 cars.
Estimated cost: $12,000-18,000
Valley Pan Coolant Pipe Corrosion
Common · high severityTypical onset: 90,000-150,000 mi
Symptoms: coolant loss with no visible external leaks, overheating, white smoke from exhaust after startup, coolant in oil (milky dipstick), rapid temperature fluctuations
Fix: Aluminum coolant pipes in the valley between cylinder banks corrode and leak internally. Requires upper intake manifold removal to access. 18-24 labor hours. Must replace all valley coolant pipes, hoses, and thermostat assembly while in there. Engine flush essential afterward.
Estimated cost: $3,500-5,500
Transmission Electronics Failure (A5S560Z)
Common · high severityTypical onset: 100,000-140,000 mi
Symptoms: intermittent limp mode (stuck in 3rd gear), harsh shifts or no shifts, transmission fault light, no reverse or no forward gears, erratic shifting patterns when hot
Fix: The valve body electronics and conductor plate fail, or the external transmission control module (TCM) dies. Valve body rebuild with new conductor plate and solenoids: 8-12 hours. TCM replacement if external: 2-3 hours. Often both needed. Must use quality reman parts; cheap ones fail quickly.
Estimated cost: $2,800-4,500
Front Thrust Arm Bushings and Ball Joints
Common · medium severityTypical onset: 70,000-110,000 mi
Symptoms: clunking over bumps, vague steering feel and wandering, inside tire wear, vibration during braking, steering wheel off-center
Fix: E38 front suspension uses large thrust arms with press-in bushings and integral ball joints. Bushings crack and ball joints wear. Must replace complete arms (not serviceable separately). 4-6 hours per side including alignment. Do both sides, all four control arms, and alignment together.
Estimated cost: $1,800-2,800
Xenon Headlight Ballast and Igniter Failure
Occasional · low severitySymptoms: one or both headlights not turning on, intermittent headlight operation, flickering, headlight works then shuts off after warmup
Fix: Early Hella xenon systems have ballasts and igniters that fail. Each assembly is 1-1.5 hours to replace (bumper removal required for proper access). OEM parts are $800+ each; quality aftermarket options exist. Bulbs rarely the issue—almost always electronics.
Estimated cost: $900-1,600
Fuel Pump and Fuel Level Sender Failure
Occasional · medium severityTypical onset: 110,000-160,000 mi
Symptoms: no start or extended cranking, stalling when fuel level below half tank, inaccurate or stuck fuel gauge, whining noise from rear, loss of power under load
Fix: In-tank fuel pump assembly includes pump and level sender that fail separately or together. Tank must be dropped. 5-7 hours labor. Replace complete assembly, not just pump. Ethanol fuel accelerates failures. Filter integrated into pump on this chassis.
Estimated cost: $1,200-1,900
Window Regulator Mechanism Failure
Common · low severitySymptoms: window dropping into door, slow or binding window operation, window stuck down or up, clicking or grinding noises, window tilts when moving
Fix: Plastic guides and regulator mechanisms break. Most common on driver door. 2-3 hours per door. Must use metal-reinforced aftermarket regulators; OEM replacements fail again. All four doors usually need service by 15-20 years regardless of mileage.
Estimated cost: $400-700
Only buy if you're mechanically inclined with a $10k reserve fund, or you're getting it cheap enough to afford an inevitable engine rebuild—otherwise, buy the 740i inline-six instead.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.