1980 BMW 630CSI

Typical onset: 90,000-140,000 mi

Symptoms: Harsh or delayed shifting between gears, Transmission fluid leaking from cooler lines or radiator-mounted cooler, Slipping under acceleration or complete loss of forward gears, Burnt transmission fluid smell

Fix: The ZF 3HP22 automatic is the Achilles heel of this car. Oil cooler lines crack and leak, contaminating the transmission with moisture. Once internal damage occurs, expect a rebuild or replacement. Cooler line replacement alone: 2-3 hours. Full transmission rebuild: 12-16 hours, often requiring removal.

Estimated cost: $400-800 for cooler/lines only, $2,800-4,500 for rebuild

Typical onset: 150,000-200,000 mi

Symptoms: Excessive oil consumption (more than 1 quart per 1,000 miles), Deep knocking or rattling from crankcase at idle, Low oil pressure at hot idle (below 10 psi), Blue smoke on startup or acceleration

Fix: Worn piston rings and main bearings are common on high-mileage M30s that missed oil changes. Rings can be done in-chassis (25-30 hours), but most shops pull the engine for a complete rebuild including bearings, timing components, and valve work. Short block replacement: 20-24 hours.

Estimated cost: $4,500-7,500 for complete engine rebuild

Symptoms: Hard starting when hot, starts fine cold, Rough idle or stalling at operating temperature, Erratic throttle response or hesitation, No-start with strong fuel smell

Fix: The early D-Jetronic system uses unreliable thermal time switches, pressure sensors, and an ECU that fails from heat exposure. Diagnosis is time-consuming (2-4 hours) because there are no scan tools. Failed thermal time switch: 1 hour. ECU replacement (often used): 1.5 hours plus $400-800 for the unit. Many owners retrofit to L-Jetronic or Weber carbs.

Estimated cost: $600-1,800 depending on component

Typical onset: 60,000-100,000 mi

Symptoms: Overheating in traffic or at highway speeds, Coolant leaking from water pump weep hole, Radiator end tank cracking (plastic tanks on later replacements), Heater not producing adequate heat

Fix: Original brass radiators crack at the tanks, and replacement aluminum units often fail prematurely. Water pumps leak or fail at the bearing. Replace both together as preventive maintenance. Radiator: 3-4 hours. Water pump: 2-3 hours. Add thermostat, hoses, and full system flush.

Estimated cost: $800-1,400 for complete cooling system overhaul

Typical onset: 80,000-120,000 mi

Symptoms: Clunking from rear end over bumps or during acceleration, Vibration at highway speeds, Visible cracking in subframe mounts or body, Differential appears to sag or shift

Fix: The rubber subframe and differential mounts deteriorate, allowing excessive movement. Subframe mounts require removal of the entire assembly (8-10 hours). Differential mounts alone: 3-4 hours. Some cars show body rot around mount points requiring welding (add 4-6 hours).

Estimated cost: $1,200-2,500 including labor

Symptoms: Intermittent gauge failures (fuel, temp, speedo), Windows or power accessories working sporadically, No-start with no dash lights, Accessories staying on after key removal

Fix: The fuse box and relay board under the dash corrode from age and moisture. Diagnosis is tedious (1-3 hours). Clean and refurbish fusebox: 2 hours. Individual relay replacement: 0.5-1 hour each. Main harness issues require extensive tracing (4-8 hours).

Estimated cost: $300-1,200 depending on extent