1998 Saab 900 2.0L Petrol · R823 AGC

Body rust is the classic 9000 killer: steel sills, jacking points, door bottoms, rear wheelarch trailing edges, sunroof and windscreen surrounds and the lower tailgate seams all corrode, accelerated by UK winter salt. Because the sills and jacking points are load-bearing, advanced corrosion is an MOT failure and can be expensive to weld properly. Early CC cars and neglected examples are worst affected, and structural rot can make the car uneconomic to repair.

The B234 2.3-litre engine drives its twin overhead camshafts and two balance shafts by chain. With infrequent oil changes the timing chain, balance chain, guides and tensioners wear, causing a start-up rattle and eventually camshaft-to-crankshaft drift. Because the B234 is an interference engine, a snapped chain can bend valves and destroy the engine, so any chain rattle should be investigated before purchase.

Turbochargers - Garrett T25 on early cars, Mitsubishi TD04 on later 2.3 and Aero models - are wear items at high mileage. Oil starvation from blocked pickups or sludge, or a leaking oil feed, wrecks the bearings: the spool becomes noisy, boost drops and blue smoke appears. A failed turbo can dump oil into the intercooler and inlet and risk a runaway, so noisy or smoking turbos need urgent attention before they cause expensive engine damage.