Subaru Impreza: FB20 Excessive Oil Consumption — Piston Ring Seal Degradation

The FB20 naturally aspirated engine introduced in the GE-facelift and carried into GH/GJ variants uses low-tension piston rings designed to reduce friction and improve fuel economy. Under predominantly short-trip or urban driving conditions the rings do not fully seat against the cylinder walls due to insufficient operating temperature, and a thin carbon deposit builds up on the ring lands. This causes the rings to stick in their grooves and lose contact with the bore, allowing engine oil to be drawn into the combustion chamber and burned. Affected engines consume 0.5–1.5 litres of oil per 1,000 km with no external leak and no blue smoke under steady cruising, though puffs of blue-grey smoke at start-up or on overrun are characteristic.

• Oil level drops 0.5–1.5 litres between standard service intervals with no visible external leak
• Blue-grey smoke from exhaust on cold start or when releasing throttle from high rpm
• Oil-fouled spark plugs on inspection, particularly cylinders 1 and 3
• Dipstick reads low or below minimum within 3,000 km of last oil change

1. 1

   Check the oil level on the dipstick and ask when it was last topped up; compare against claimed service interval.

2. 2

   Inspect the spark plugs for oil fouling (dark, wet deposits on electrode).

3. 3

   Look for blue-grey puff of smoke from exhaust during a cold start and again when lifting off throttle from 4,000 rpm.

4. 4

   If a workshop inspection is possible: Perform a leakdown test on each cylinder — a healthy FB20 should hold above 90% pressure.

$180 to $5,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “How often do you check and top up the oil between services?”
• “Has Subaru or a mechanic ever assessed this car for oil consumption under a consumption test?”
• “Are the service records available showing oil type and quantity used at each service?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.