Question 1

1. Front Subframe Mount Corrosion

Accepted Answer

The front subframe mounting points corrode from road spray and accumulated grime. In advanced cases, the mount tears away from the body under braking or over bumps, causing a complete loss of front suspension geometry. The subframe mounts are box sections that trap moisture and road salt. The factory underseal deteriorates with age, exposing bare metal. Australian cars suffer less than European examples, but coastal and rural cars (gravel road spray) are still affected. Mild surface corrosion can be treated with rust converter and cavity wax. Structural corrosion requires cutting out the affected metal and welding in new fabricated sections. Cost: $1,500-4,000 depending on severity. This is a job for an experienced fabricator, not a panel beater.

Question 2

2. Rear Trailing Arm Pickup Point Corrosion

Accepted Answer

The rear trailing arm mounting points weaken from corrosion, causing the rear suspension to shift under load. Symptoms include vague rear-end handling, uneven rear tyre wear, and clunking from the rear when cornering. The same moisture-trapping box section issue as the front subframe. The trailing arm mounts also bear significant dynamic loads, so even mild corrosion weakens them beyond safe limits faster than a static panel. Reinforcement plates welded over the existing mounts. If the original metal is too far gone, the entire section needs cutting and fabricating. Cost: $1,000-3,000. Inspect from below on a hoist.

Question 3

3. Windscreen Surround Corrosion

Accepted Answer

Bubbling paint around the windscreen edges, particularly at the lower corners. By the time paint is bubbling, the underlying metal is often perforated. The rubber windscreen seal traps moisture against the pinch weld. The factory sealant under the glass deteriorates with age, allowing water ingress between the glass and the body. UV exposure in Australia accelerates the rubber seal degradation. The windscreen must be removed to properly repair the surround. Corroded metal is cut out and new metal welded in. The windscreen is refitted with new sealant and seal. Cost: $2,000-4,000. This is not a job you can ignore, water entering the cabin causes further damage to the footwells and wiring.

Question 4

4. Door Bottom Corrosion

Accepted Answer

The lower edges of the doors develop rust bubbles. In advanced cases, the door skin perforates. Paint appears to blister from the inside out. The E24's pillarless doors have drain holes at the bottom that block with road grime and sealant residue. Water entering through the window channels collects inside the door and cannot escape. The water sits against the door skin and corrodes from the inside. Clear the drain holes as preventive maintenance. Once the door skin is perforated, repair involves cutting out the corroded section and welding in new metal, or sourcing a replacement door shell, which is increasingly difficult and expensive. Repair cost: $800-2,000 per door. Replacement doors: $1,500-3,000 when available.

Question 5

5. Timing Chain and Tensioner Wear

Accepted Answer

Rattling noise from the front of the engine on cold start, lasting 2-10 seconds until oil pressure builds. In severe cases, the rattle persists when warm. If the chain jumps teeth, the engine timing shifts and performance drops dramatically, in worst cases, valve-to-piston contact occurs. The M30 uses a single-row timing chain with a hydraulic tensioner. Over 200,000+ km, the chain stretches and the tensioner guide rails wear. The hydraulic tensioner relies on oil pressure, when the engine sits, oil drains from the tensioner, allowing the chain to slap on startup. Replace the timing chain, tensioner, guide rails, and sprockets. This is a front-of-engine job requiring removal of the radiator and front covers. Cost: $800-1,500 at a specialist. Parts: chain (Iwis OEM, ~$80), tensioner (~$150), guide rails (~$100), sprockets (~$200). The Iwis brand chain is the only one to use, cheap aftermarket chains stretch rapidly.

Question 6

6. Bosch L-Jetronic Fuel Injection Issues (Early 633CSi)

Accepted Answer

Rough idle, hesitation on acceleration, rich or lean running, poor fuel economy. The engine may start fine cold but run poorly once warm, or vice versa. The L-Jetronic system uses an analogue air flow meter (flap-type) and a series of sensors to determine fuelling. After 40+ years, the air flow meter potentiometer wears, the coolant temperature sensor drifts out of calibration, and the wiring harness connectors develop resistance from oxidation. Vacuum leaks from perished rubber hoses compound the problem. Systematic diagnosis starting with vacuum leak testing, then checking sensor outputs with a multimeter. The air flow meter is the most common single point of failure, rebuild kits are available ($150-250) or replacement units cost $400-800. The coolant temperature sensor (NTC type, Bosch 0280130026) is cheap at $30-50 and should be replaced proactively. Wiring harness connector cleaning and re-pinning: $200-400 at a specialist.

Question 7

7. Oil Leaks

Accepted Answer

Oil residue on the engine and components. Oil smell in the cabin from oil dripping onto the exhaust manifold. Oil spots on the garage floor. Every gasket and seal on a 40-year-old M30 will eventually leak. The most common sources: valve cover gasket (cork, hardens and shrinks), oil filter housing O-ring (hardens and cracks), oil pan gasket (cork or rubber, deteriorates), front crank seal, and rear main seal. Full engine reseal. Replace all gaskets and seals in one session. The valve cover gasket is a 30-minute job. The oil filter housing O-ring is a one-hour job. The oil pan gasket requires lifting the engine or dropping the subframe. The rear main seal requires gearbox removal. Full reseal cost: $400-600 DIY, $1,000-2,000 at a workshop. Critical: the oil filter housing O-ring leaks onto the exhaust manifold and is a fire risk, prioritise this one.

Question 8

8. Valve Clearance Drift

Accepted Answer

Ticking from the top end of the engine, particularly when warm. Loss of power in the affected cylinders. In severe cases, exhaust valves burn from insufficient clearance (running too tight). The M88 uses bucket-and-shim valve adjustment. Unlike hydraulic lifters, the clearances change as the valve seats wear and the shims bed in. BMW specified checking every 20,000 km, which many owners defer. Valve clearance check and shim replacement. The camshafts must be removed to access the shims. This requires specialist tooling and knowledge, do not attempt this on a roadside. Cost: $400-600 at an M-car specialist. Shims are available from BMW (part numbers vary by thickness, $10-20 each) and aftermarket suppliers.

Question 9

9. Cooling System Degradation

Accepted Answer

Overheating. Coolant leaks from hoses, the expansion tank, or the radiator. The temperature gauge creeps above normal, particularly in traffic or on hot days. Every rubber and plastic component in the cooling system degrades with age and heat cycling. The expansion tank becomes brittle and cracks. Rubber hoses harden, crack, and blow off their connections. The original radiator develops internal blockages that reduce cooling capacity. The thermostat sticks closed, preventing coolant flow. Replace the entire cooling system proactively: radiator ($300-600), all hoses ($150-300 for the set), expansion tank ($60-100), thermostat ($40-60), and water pump ($120-200). Total parts cost: $700-1,200. This is preventive maintenance, not a repair, if you wait for components to fail, you'll overheat the engine and cause far more expensive damage. Use a brass/copper or aluminium aftermarket radiator for better cooling than the original plastic-tanked unit.

Question 10

10. Differential Mount Bushings

Accepted Answer

Clunking from the rear of the car when accelerating from a stop, decelerating, or going over bumps. The clunk comes from the differential shifting in its mounts. The rubber differential mount bushings perish with age and lose their damping ability. The differential rocks in its cradle, banging against the mount brackets. Replace the differential mount bushings. This is a straightforward job on a hoist, support the differential, remove the mount bolts, press out the old bushings, press in new ones. Parts: $60-120 for the bushing set. Labour: 1-2 hours. Polyurethane bushings are available and last longer but transmit more NVH.

Question 11

11. Guibo (Flex Disc) Deterioration

Accepted Answer

Vibration from the drivetrain, felt through the floor and seats. In severe cases, a rhythmic clunking at low speed. If the guibo fails completely, the driveshaft disconnects from the gearbox. The guibo is a rubber disc that connects the gearbox output flange to the driveshaft. It absorbs drivetrain shock loads and accommodates slight misalignment. After decades, the rubber cracks, tears, and eventually fails completely. Replace the guibo. Inspect it visually, any visible cracking in the rubber means it needs replacing. Cost: $80-150 for the part, 1-2 hours labour. Always replace the guibo bolts at the same time, they are stretch bolts and must not be reused.

Question 12

12. Steering Box Wear

Accepted Answer

Excessive play in the steering. The car wanders at highway speed. The steering feels vague off-centre and requires constant correction. The E24 uses a recirculating-ball power steering box. The internal ball bearings and races wear over time, introducing play. The adjustment screw on the box can take up some slack, but excessive adjustment causes binding. A rebuilt steering box is the proper fix. Do not over-tighten the adjuster, this causes the steering to bind at certain angles. Rebuilt units: $800-1,200 exchange. Fitting: 2-3 hours. A specialist can rebuild your unit for $600-900. Aftermarket aftermarket ZF-type boxes are available but quality varies.

Question 13

13. Front Strut Tower Cracking

Accepted Answer

Cracks appear in the sheet metal around the front strut top mount. In advanced cases, the strut tower deforms under load, changing the front suspension geometry. The strut towers absorb significant dynamic loads from the front suspension. Over decades, the sheet metal fatigues, particularly if the car has been driven on rough roads or with worn strut top mounts that transmit impact loads directly to the tower. Mild cracking can be welded and reinforced. Severe cracking may require cutting in new metal. Strut tower reinforcement plates are available ($100-200) and should be fitted proactively. Cost for repair: $500-1,500 depending on severity.

Question 14

14. Dashboard Cracking

Accepted Answer

Cracks appear across the top of the dashboard, particularly on the passenger side and around the instrument binnacle. The cracks deepen with time until the dashboard surface disintegrates. The E24 dashboard is made of a foam-backed vinyl material that is extremely sensitive to UV radiation. In Australia's harsh sunlight, dashboard cracking is virtually universal. Even cars that have been garaged will develop cracks if the dashboard has had any significant sun exposure. There is no economical repair for a cracked E24 dashboard. Options: source a replacement dashboard from a wrecked car ($1,500-3,000, they are extremely scarce), have the dashboard recovered by a trimmer ($800-1,500), or fit a dashboard cap ($300-500, but they look aftermarket). A windscreen sunshade from day one is the best prevention.

Question 15

15. Window Regulator Failure

Accepted Answer

The electric windows stop working, operate intermittently, or make grinding noises when operating. One or both windows may drop into the door and refuse to come back up, a significant problem on a pillarless coupe, as the window must seal against the roof line with no door frame for support. The window regulators use a cable-and-pulley system with a small electric motor. The cables fray, the pulleys seize, and the motors burn out. The guides that the glass runs in also wear, causing the window to bind. Replace the regulator assembly. Parts: $200-400 per regulator. Labour: 2-3 hours per door (the inner door panel removal and regulator fitting is fiddly). Lubricate the window channels with silicone spray as preventive maintenance every six months.

E24 6-Series

E24 6-Series known problems