1989 BMW 635CSI

Typical onset: 100,000-150,000 mi, but age-related failures occur even at lower miles

Symptoms: Harsh 2-3 shift or refusal to shift into third gear, Slipping between gears, especially when warm, Transmission fluid appears burnt or smells acrid, Delayed engagement into Drive or Reverse

Fix: Full rebuild with updated seals, clutch packs, and valve body reconditioning. 12-16 hours labor. Many techs recommend replacing the external oil cooler and all cooler lines at the same time since the transmission must come out anyway.

Estimated cost: $2,800-4,500

Typical onset: 120,000+ mi, or after repeated overheating episodes

Symptoms: White smoke from exhaust, especially on cold start, Coolant mysteriously disappearing with no visible leaks, Oil cap shows milky residue, Rough idle and misfires on cylinders 5 and 6 (rear of engine)

Fix: Head removal, magnaflux inspection, machining or replacement. If head is cracked between valves (common on cylinders 5-6), replacement is required. Factor in timing chain, guides, and valve stem seals while apart. 18-24 hours labor for head gasket; 25-32 hours if head needs replacement and full top-end refresh.

Estimated cost: $3,200-6,800

Symptoms: Hard starting after sitting, especially hot restart issues, Rough idle and hesitation under acceleration, Fuel smell in cabin or around rear of car, Fuel pressure drops rapidly after engine shut-off

Fix: Original Bosch injectors get clogged; fuel accumulator (damper) diaphragm fails; in-tank pump weakens. Complete refresh includes pump, filter, accumulator, and injector cleaning or replacement. In-tank pump requires dropping the tank (4-5 hours); injector service adds another 3-4 hours. Most shops bundle this work.

Estimated cost: $1,800-3,200

Symptoms: Coolant leaks from radiator end tanks (plastic becomes brittle), Expansion tank cracks and sprays coolant, Water pump bearing noise or weeping from weep hole, Heater core leaks into passenger footwell

Fix: The entire cooling system needs preventive overhaul on any 635CSi unless documented in last 5 years. Radiator, expansion tank, upper/lower hoses, thermostat, water pump, and all rubber connections. Water pump is 4 hours; full system overhaul is 8-10 hours if heater core is included (dash removal).

Estimated cost: $1,200-2,800 (without heater core), $3,500-5,000 (with heater core)

Symptoms: Excessive vibration at idle, especially with A/C on, Clunk when shifting from Park to Drive or Reverse, Visible engine movement when revving in Park, Driveline shudder during acceleration

Fix: All three engine mounts and the transmission mount are hydraulic and fail from age. Must be replaced as a set. 3-4 hours labor.

Estimated cost: $800-1,400

Typical onset: 80,000-130,000 mi

Symptoms: Clunking over bumps from rear suspension, Steering feels vague and rear end wanders on highway, Visible tears in large rubber subframe mounts, Differential movement visible when rocking car in gear

Fix: Rear subframe has large rubber mounts that tear and allow the entire subframe to shift. Requires subframe drop, pressing out old bushings, pressing in new. 6-8 hours labor if differential bushings are also done.

Estimated cost: $1,200-2,000

Symptoms: Check Control lights illuminate randomly (oil level, coolant, brake pad sensors), Gauges read erratically or stop working (fuel gauge, temp gauge), OBC (on-board computer) display dims or fails, Turn signal relay clicks rapidly or doesn't self-cancel

Fix: Most issues trace to corroded grounds, failing sensors, or aged solder joints on instrument cluster circuit boards. Cluster removal and resoldering is 3-4 hours. Grounds are 1-2 hours to chase and clean. Sensors are cheap but time-consuming to diagnose.

Estimated cost: $400-1,200