964

1989-1994 / Coupe / Targa / Cabriolet / Germany

Minor Electrical and Ancillaries

14. Cylinder Head Stud Issues

Symptoms

Sudden loss of power on one cylinder bank. Misfiring. Coolant or oil mixing (visible at the cylinder base). In severe cases, a loud pop or exhaust blow. ---

Cause

The M64 crankcase is magnesium alloy, and the head studs thread into this relatively soft material. Overheating episodes, repeated thermal cycling to extreme temperatures, and high mileage weaken the thread engagement. An overheating event, even a brief one, can be the trigger. Modified engines with increased power output are at higher risk.

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// More 964 problems

Other known issues

Critical Electrical and Ancillaries

11. Wiring Harness Degradation

Intermittent electrical faults (lights flickering, gauges misbehaving, windows not operating). Blown fuses. Evidence of rodent nesting in the engine bay or front boot.

Critical Electrical and Ancillaries

12. Heater Box and Heat Exchanger Corrosion

Exhaust smell inside the car when the heater is on. Headaches or drowsiness while driving (carbon monoxide exposure). Visible corrosion or rust on the heat exchangers when inspected from below.

Common Electrical and Ancillaries

13. Window and Sunroof Seal Leaks

Damp carpets, musty smell, water stains on the headliner. Water visible in the footwells after rain.

Common Engine

1. Oil Leaks (Chain Tensioner Housings)

Oil residue on the engine's lower surfaces, oil drips on exhaust components (burning oil smell), oil spots beneath the car.

Common Engine

2. Oil Leaks (Cam Cover Gaskets)

Oil on the cylinder heads and barrel surfaces, burning oil smell from exhaust contact.

Critical Engine

3. Oil Leaks (Cylinder Base Gaskets)

Oil around the cylinder bases, dripping down the engine. In severe cases, oil loss between services.

All 964 problems