Question 1

Timing Belt Failure

Accepted Answer

The engine stops instantly while driving. If the belt snaps at speed, the valves collide with the pistons, destroying the cylinder head and potentially the pistons as well. The engine is scrap without a full rebuild. The M20 has an unusual design, a timing chain drives the camshaft from the front, while a separate timing belt at the rear of the engine drives the intermediate (auxiliary) shaft. This belt is made of rubber and degrades with age and heat regardless of mileage. The belt is hidden at the back of the engine, against the firewall, so it's out of sight and out of mind. Many owners forget about it until it's too late. Replace the timing belt, tensioner, and water pump every 60,000-80,000 km or every 4 years, whichever comes first. The job requires removing the intake manifold and various components to access the rear of the engine. It's a 4-6 hour job for an experienced mechanic. Cost: $400-700 at a specialist. DIY cost: $80-150 in parts.

Question 2

Head Gasket Failure

Accepted Answer

Coolant loss without visible external leak. White smoke from the exhaust (coolant burning in the combustion chamber). Overheating. Milky emulsion under the oil filler cap. Coolant in the oil (oil level rises, oil appears grey or milky on the dipstick). Bubbles in the expansion tank with the engine running. The M20 head gasket is a known weak point. The head bolts are stretch-to-yield (torque-to-yield) design that loses clamping force over time. Thermal cycling and the aluminium head expanding at a different rate to the iron block contribute to gasket failure. Overheating events, even brief ones, dramatically increase the risk of head gasket failure. Replace the head gasket with the head removed and resurfaced. Use ARP head studs instead of the factory stretch bolts, this is the single best preventive modification for the M20. Cost: $1,200-2,000 at a workshop; $300-500 DIY if the head doesn't need machining. ARP head studs: $250-350.

Question 3

Oil Leaks, Everywhere

Accepted Answer

Oil weeping from the valve cover gasket, oil filter housing gasket, oil pan gasket, rear main seal, and front crank seal. A high-mileage M20 will have oil residue on virtually every surface. Cork and rubber gaskets degrade over 30+ years. The M20 uses a variety of gasket materials, and all of them fail eventually. The oil filter housing gasket is particularly notorious, it's a large O-ring that hardens and leaks oil onto the exhaust manifold, creating smoke and a fire risk. Reseal the engine systematically. Replace all gaskets and seals in one session rather than chasing individual leaks. The oil filter housing gasket is the most urgent (fire risk). The valve cover gasket is the easiest to do. The rear main seal requires gearbox removal. Cost for a full reseal: $300-600 DIY, $800-1,500 at a workshop.

Question 4

Idle Control Valve (ICV) Failure

Accepted Answer

Rough idle, idle speed hunting (revs surging up and down between 500 and 1,500 rpm), stalling when coming to a stop, or idle sitting too high (1,200+ rpm). The engine may idle fine when cold but develop problems as it warms up. The ICV is an electrically controlled air bypass valve that regulates idle speed. Carbon deposits from crankcase ventilation blowby clog the valve's passages. The valve's internal motor can also fail electrically. Remove and clean the ICV with carburettor cleaner or brake cleaner. Spray cleaner into both ports and through the valve while working the valve open and closed. Allow to dry completely. If cleaning doesn't resolve the issue, replace the ICV. Cost: $0 for cleaning, $100-200 for a replacement valve.

Question 5

Timing Belt and Chain Issues

Accepted Answer

Rattling noise on cold start from the front of the engine (chain). Engine misfiring or loss of power (belt). The M40, like the M20, has both a timing chain and a timing belt. The chain tensioner weakens with age, allowing the chain to slap against its guides. The timing belt at the rear degrades with age. If the chain jumps a tooth, valve timing shifts and the engine runs poorly. If the belt snaps, it's catastrophic. Replace the timing belt every 60,000 km. If the chain is rattling, replace the chain, tensioner, and guides, this requires front cover removal. Cost: $300-600 for belt service, $500-900 for chain service.

Question 6

Crankcase Ventilation (CCV) Failure

Accepted Answer

Oil consumption increases, rough idle, oil leaks, whistling noise from the engine, check engine light. The crankcase ventilation valve (CCV) and associated hoses become brittle and crack. When the CCV fails, crankcase pressure builds up, forcing oil past seals and gaskets. This is a hidden cause of many oil leaks, replacing gaskets without fixing the CCV is pointless. Replace the CCV valve and all connected hoses. Inspect the oil separator as well. Cost: $50-120 for parts.

Question 7

Expansion Tank Cracking

Accepted Answer

Coolant leak from the expansion tank, often sudden and catastrophic. The tank may crack along a seam or at the neck where the cap sits. Coolant pours out, the engine overheats within minutes. The plastic expansion tank is subjected to constant pressure and temperature cycling. After 10+ years, the plastic becomes brittle and cracks without warning. This is the most common cause of sudden overheating in E30s. Replace the expansion tank. This is a proactive maintenance item, don't wait for it to fail. Replace every 5-7 years regardless of condition. Cost: $40-80 for the tank.

Question 8

Water Pump Failure

Accepted Answer

Overheating, coolant leak from the front of the engine, whining or grinding noise from the water pump area. In worst cases, the plastic impeller breaks apart and pieces circulate through the cooling system, blocking the heater core and radiator passages. The factory water pump uses a plastic impeller that degrades with age and coolant contamination. The pump bearing also wears, causing the shaft to wobble and the seal to leak. Replace with a metal-impeller water pump. Always replace the thermostat and coolant at the same time. Cost: $100-180 for a quality metal-impeller pump. Total cooling service: $200-400 DIY.

Question 9

Thermostat Housing Cracking

Accepted Answer

Coolant leak from the thermostat housing. May be a slow weep or a sudden crack. The aluminium thermostat housing corrodes from the inside when coolant is not changed regularly. The housing can also crack from thermal stress if the thermostat sticks closed and the housing is subjected to extreme temperature differentials. Replace the thermostat housing and thermostat together. Cost: $60-120 for housing and thermostat.

Question 10

Rear Shock Tower Corrosion

Accepted Answer

The sheet metal around the rear shock absorber mounting points corrodes and weakens. In severe cases, the shock pushes through the floor of the boot. The car may sit unevenly, or you may hear clunking from the rear. Water enters the boot through deteriorated taillight seals and sits in the spare tyre well. Moisture wicks up into the shock tower area. Road spray from underneath also attacks the metal. The double-skinned construction traps moisture between layers. Mild surface rust can be treated with rust converter and sealed. Structural corrosion requires cutting out the affected metal and welding in repair panels or fabricated patches. This is a specialist job. Cost: $500-1,500 per side for minor repair, $1,500-3,000 per side for severe corrosion.

Question 11

Battery Tray Corrosion

Accepted Answer

The battery tray (in the engine bay, passenger side) corrodes through. Acid from the battery eats through the metal tray and then attacks the chassis rail underneath. Battery acid vapour and minor spills corrode the mild steel tray. Old batteries that vent acid during charging accelerate the process. Remove the battery and inspect the tray. Surface corrosion: wire brush, treat with rust converter, prime and paint. Perforation: weld in a repair patch or fabricate a new tray. Inspect the chassis rail beneath, if it's corroded, professional repair is required. Cost: $100-300 for tray repair, $500-1,500 if the chassis rail is affected.

Question 12

Front Subframe Mount Corrosion

Accepted Answer

Cracking, crumbling, or perforation of the unibody metal where the front subframe bolts to the chassis. May be visible as rust around the subframe bolt holes when viewed from underneath. Road spray and trapped moisture corrode the mount points from the outside. Salt exposure (less common in Australia than in Europe) accelerates it. The double-skinned construction hides the corrosion until it's severe. Professional repair involving cutting out corroded metal and welding in reinforcement plates. Not a DIY job. Cost: $1,000-3,000 depending on severity.

Question 13

Jacking Point Corrosion

Accepted Answer

The factory jacking points crumble when you try to jack the car up. The jack punches through the corroded metal. The jacking points are box-section pressed steel that traps moisture. They rust from the inside out and look fine until you apply force. Welded repair with reinforcement plates. Cost: $200-500 per point. This problem usually indicates more extensive hidden rust, use it as a warning sign to inspect the entire underside thoroughly.

Question 14

Differential Mount Failure

Accepted Answer

Clunking from the rear of the car under acceleration, deceleration, and gear changes. The rear of the car may feel imprecise. A failed mount allows the differential to shift on its subframe, which changes the driveshaft alignment. The large rubber bushing that mounts the differential to the rear subframe tears and separates with age. Hard acceleration and aggressive driving accelerate the failure. Replace the differential mount bushing. Access requires supporting the differential and removing the mounting bolt. Cost: $80-150 for the bushing. Some owners upgrade to polyurethane or Delrin mounts for a firmer feel, but these transmit more NVH into the cabin.

Question 15

Guibo (Flex Disc) Failure

Accepted Answer

Vibration through the driveline, clunking during gear changes, visible cracks in the rubber disc between the gearbox output flange and the propshaft. The guibo is a rubber coupling that absorbs driveline shock. It degrades with age, heat, and oil contamination. The rubber cracks circumferentially and eventually separates. Replace the guibo. Inspect at every service, if cracks are visible, replace immediately. A separated guibo at speed allows the propshaft to flail freely. Cost: $60-100.

Question 16

Window Regulator Failure

Accepted Answer

The window drops into the door, sticks halfway, or moves slowly and unevenly. A grinding or clicking noise may precede failure. The E30 uses cable-driven window regulators. The steel cable frays from age and repeated use. The cable guide pulleys also seize. Replace the window regulator assembly. This is one of the most common E30 repairs. Cost: $80-150 per door for aftermarket regulators.

Question 17

Instrument Cluster Pixel Failure

Accepted Answer

The LCD display for the odometer, service indicator, and other digital readouts fades, becomes spotty, or goes blank. The analogue gauges continue to function. The ribbon cable connections and solder joints on the LCD module crack from thermal cycling. The display module loses connection to the cluster circuit board. Re-solder the ribbon cable connections on the LCD module. Repair kits with replacement ribbon cables are available for $20-50. The cluster must be removed from the car. Requires basic soldering skills. A specialist can do the repair for $100-200.

Question 18

Dashboard Cracking

Accepted Answer

The dashboard surface develops cracks, particularly across the top and around the defroster vents. The cracks worsen over time and can't be repaired to factory appearance. The dashboard material (PVC foam over a metal frame) shrinks and becomes brittle from UV exposure and heat. Australian conditions accelerate this dramatically compared to European cars. No good repair. Used replacement dashboards are $500+ and also tend to be cracked. Dashboard covers ($40-80) are the practical solution. Some specialists offer dashboard re-skinning for $800-1,500.

Question 19

Front Strut Mount Bearing Failure

Accepted Answer

Creaking or grinding noise when turning the steering wheel, especially at low speed or standstill. Clunking over bumps. Vague or delayed steering response. The rubber and bearing assembly in the strut top mount wears from constant use. The bearing surface deteriorates, creating friction and noise. Replace the strut mount assemblies. This is usually done when replacing shock absorbers. Cost: $60-100 per side.

Question 20

Rear Trailing Arm Bushing Wear

Accepted Answer

Vague rear-end feel, clunking from the rear over bumps, uneven rear tyre wear (particularly inside edge wear). The rubber bushings in the rear trailing arms harden and crack with age. A worn bushing allows the trailing arm to move under load, changing rear wheel alignment. Replace the bushings. Polyurethane replacements are popular for improved precision but transmit more road noise. Cost: $100-200 per side for rubber, $150-300 for polyurethane.

E30 3-Series

E30 3-Series known problems