1987 BMW 733I

Typical onset: 80,000-150,000 mi

Symptoms: Transmission clunk on throttle application or deceleration, Pink or red fluid pooling under vehicle center, Erratic shifting or slipping when hot, Visible sagging of transmission tailshaft

Fix: Transmission mount collapses from age and heat, often puncturing or stressing the cooler lines. Requires trans support, mount replacement (2-3 hrs), and cooler line or full cooler replacement if leaking (add 1-2 hrs). Fluid flush mandatory after repair. If driven low on fluid, internal clutch damage requires rebuild.

Estimated cost: $600-1,200 for mount and cooler; $2,500-4,000 if transmission rebuild needed

Typical onset: 100,000+ mi or 10+ years between services

Symptoms: Rough idle, hesitation, or lean misfire under load, Check engine light with lean codes, Metallic rattle from engine on cold start, Excessive oil consumption (more than 1 qt per 1,000 mi)

Fix: Clogged fuel filter (often original from 1987) starves injectors, causing lean conditions that score Nikasil cylinder liners. Early catch: replace filter ($80 part, 0.5 hrs). Once scored: requires engine-out short block replacement or full rebuild with re-sleeving (25-35 hrs labor). This is the single most expensive failure on this chassis.

Estimated cost: $80-150 for filter; $8,000-14,000 for short block or rebuild with sleeves

Typical onset: 120,000-180,000 mi

Symptoms: Rattling from front of engine for 2-5 seconds after cold start, Loss of power and rough running, Check engine light with cam/crank correlation codes, Metal shavings in oil filter during change

Fix: M30 timing chains stretch and guides disintegrate when oil change intervals exceed 5,000 mi. Chain replacement requires front-end disassembly, upper and lower guides, tensioner rail, and new chain (12-16 hrs). If chain jumps timing, expect bent valves requiring head work (add 8-12 hrs).

Estimated cost: $2,000-3,500 for chain service; $4,500-6,500 if valves damaged

Typical onset: 90,000-140,000 mi

Symptoms: Oil spots on driveway centered under bellhousing area, Visible oil seepage at engine-to-transmission joint, Oil dripping from front of oil pan after sitting, Low oil level between changes despite no visible smoke

Fix: Age-hardened rubber seals weep oil. Rear main requires transmission removal (8-10 hrs). Oil pan gasket is easier but requires subframe drop or significant clearance work (4-6 hrs). Both are preventive—not driving risks, but mess and oil loss add up. Often done together when trans is out for other work.

Estimated cost: $1,200-1,800 rear main; $600-1,000 oil pan; $1,800-2,500 both together

Symptoms: Intermittent no-start when hot, starts fine cold, Cranks but no spark or fuel pump activation, Tach drops to zero while cranking, Stranded without warning after short drives

Fix: Common Motronic failure point, especially in high under-hood temps. Sensor is on bellhousing, requires access from underneath (1-1.5 hrs). Inexpensive part ($80-150), but causes tow bills if it fails away from home. Carry a spare in the glovebox.

Estimated cost: $200-350

Typical onset: 70,000-120,000 mi

Symptoms: Burning oil smell from engine bay, especially after sitting, Oil residue on exhaust manifolds causing smoke on startup, Visible seepage along valve cover perimeter or intake valley, Oil pooling on top of bellhousing at rear of head

Fix: Cork and rubber gaskets harden with age. Valve cover is straightforward (2 hrs), valley pan requires intake manifold removal (5-7 hrs). Not urgent but makes a mess and can drip onto hot exhaust. Do both at once if intake is already off for other work.

Estimated cost: $400-700 valve cover; $800-1,400 valley pan; $1,000-1,600 both