Porsche 928 GT

Identical to the S4 engine: interference engine with two timing belts. Belt failure destroys all 32 valves and pistons. Particularly painful in the rare GT — strictly observe the 60,000 km/4-year replacement interval.

Symptoms: Engine stops abruptly, loud metallic clattering, will not start again.

Less common in the GT since most are manuals. But in the few automatic GT examples the TBF risk exists just as with the S4. Check crankshaft end float regularly.

Symptoms: Axial crankshaft play over 0.4 mm, dull knocking when accelerating/lifting off.

The GT is driven in the upper rev range more often than the S4. Camshaft sprockets wear faster, especially with track day use. Valve timing shifts gradually.

Symptoms: Power loss at high revs, light clattering from valve train, changed exhaust values.

Identical to the S4: crankcase ventilation carries oil mist into the intake with worn piston rings. The GT tends to be slightly more affected due to higher rev usage.

Symptoms: Oil smell, oil in intake, blue smoke under full load, high oil consumption.

Ceramic mechanical seal on the water pump leaks. Aftermarket mechanical seal recommended. Replace together with timing belt.

Symptoms: Coolant drops at the water pump, dropping coolant level.

Cable insulation and connectors throughout the entire wiring harness become brittle and cracked after 30–40 years. High contact resistance at corroded terminals causes multiple intermittent faults.

The rubber bushings in the Weissach rear axle harden and crack with age. The characteristic passive steering correction effect is lost, making the self-steering behaviour under braking unpredictable.

On 30–40 year old cars, steel brake lines are often heavily corroded. Caliper pistons seize from old brake fluid. A full brake system check is mandatory at purchase.

The flexible circuit foil in the instrument cluster cracks with age. Over 30 bulbs in the cluster; failed solder joints cause partial loss of individual gauges. Refurbishment by specialists is possible.

The ball joints on the front double wishbones cannot be replaced individually — full control arm replacement required. Early aluminium versions were upgraded to stronger steel units.

The pop-up headlight motor corrodes internally. Connector pins in the motor housing oxidise. Headlights do not extend or only one side works. New original motors are virtually unavailable.

Doors, wings and bonnet are aluminium; the rest is galvanised steel. Contact corrosion with paint undercreep develops at the transitions. Most vulnerable: sills, wheel arches and door rubber clips.

Tailgate rubbers shrink with age. Sunroof seals and drain channels clog. Moisture in the rear cabin area and mould on the headliner are common consequences.

Older 928s have R12 AC systems that need converting to R134a. The blower motor behind the centre console frequently fails and disables the entire temperature control.

Power steering hydraulic hoses become porous and leak — fire risk if fluid drips on the exhaust. The steering rack develops play and a foamy steering feel at high mileage.

Aluminium-copper radiators corrode with incorrect coolant. The expansion tank becomes brittle and cracks. Replacing an original radiator is expensive as they are barely available any more.