1989 BMW 750I

Typical onset: 80,000-130,000 mi

Symptoms: Harsh 2-3 shift or refusal to shift out of second gear, Slipping under load especially when warm, Burnt transmission fluid smell and dark brown/black color, Erratic shifting or limp mode activation

Fix: The ZF A4S310R cannot handle the V12's torque long-term. Torque converter, solenoid pack, and clutch pack wear are typical. Rebuild requires 18-24 hours including R&R; most shops sublet to transmission specialists. Replacement torque converter, full gasket set, solenoids, and fluid flush are minimum. Many opt for updated valve body during rebuild.

Estimated cost: $3,500-6,500

Typical onset: 90,000-150,000 mi

Symptoms: Cold-start smoking that clears after warmup, Rough idle when cold with misfire codes, Progressive loss of compression in multiple cylinders, Elevated oil consumption beyond 1 quart per 1,000 miles

Fix: Pre-1992 M70 blocks used Nikasil coating that degraded with high-sulfur fuel. Compression test below 150 psi cold confirms it. Only real fix is engine replacement with Alusil block (1992+) or full shortblock rebuild with steel liners. Requires 40-50 hours for engine removal, machine work, and reinstallation. Core availability is scarce.

Estimated cost: $12,000-18,000

Typical onset: 70,000-120,000 mi

Symptoms: Intermittent misfire codes on random cylinders, Check engine light that comes and goes with temperature changes, Rough running that improves after wiggling harness connectors, Multiple sensor faults without actual sensor failure

Fix: BMW used biodegradable wire insulation that cracks and exposes conductors. The M70 has two complete engine harnesses (one per bank). Requires 12-16 hours to replace both harnesses with updated units, including proper routing and connector cleaning. Must be done with engine in car—tight quarters around the V.

Estimated cost: $2,800-4,200

Typical onset: 60,000-100,000 mi

Symptoms: Rear suspension sags overnight or after sitting, Warning light for suspension malfunction, Compressor runs constantly or not at all, Uneven rear ride height side-to-side

Fix: Electronic Height Control uses hydraulic struts, accumulator spheres, and dedicated pump. Struts leak internally, spheres lose pressure, and lines crack. Full system refresh includes both rear struts, accumulator, and pump overhaul—8-10 hours. Many convert to conventional springs/shocks for $1,500 less, sacrificing the self-leveling feature.

Estimated cost: $3,200-4,800

Typical onset: 50,000-90,000 mi

Symptoms: Overheating on one bank while the other runs normal, Coolant loss without visible external leaks, Heater works intermittently or only on one side, Steam from rear of engine valley

Fix: The M70 has dual cooling circuits with valley coolant pipes prone to corrosion perforation. Requires engine-out service to properly replace valley pipes, both radiators (yes, two), water pump, and all hoses—30-35 hours all-in. Plastic thermostat housings crack. Half-measures lead to repeat failures within 20k miles. Do it all at once or plan to do it twice.

Estimated cost: $5,500-8,000

Symptoms: Missing segments in digital odometer or trip computer, Entire LCD sections go blank or show gibberish, Intermittent display with temperature changes, Warning lights remain dim or invisible

Fix: The LCD ribbon cables deteriorate where they connect to the circuit board. Cluster must be removed (1.5-2 hours) and sent to specialist for ribbon re-soldering or LCD replacement. Turnaround is typically 3-5 days. DIY-friendly if you have soldering skills, otherwise specialist repair is mandatory.

Estimated cost: $400-800