1998 Subaru Impreza Problems: 5 Known Issues

On the 1998-1999 Subaru Impreza EJ25D (2.5L DOHC), the first-generation 2.5L DOHC boxer (EJ25D) used in the 1998-1999 Impreza 2.5 RS (and shared with the 1996-1999 Legacy/Outback/Forester of the era) is notorious for internal head gasket failure. In 1996 Subaru used a composite gasket, then from 1997 switched to a multi-layer-steel shim gasket with a graphite outer film; the film between the combustion chamber and the cooling jacket degrades (typically around 100,000 miles), allowing coolant into the combustion chamber and combustion gases into the cooling jacket. Because the flat-four has two heads and the failure is typically internal (coolant-to-combustion) rather than the external weep seen on the later 2.5 SOHC, the classic pattern is overheating on the highway that cools off in town, and it can warp a head if driven on. This is the defining reliability problem of the DOHC-era 1990s Impreza.

On the 1997-1999 Subaru Impreza, the 2.5L DOHC EJ25D and the 1997-and-later SOHC EJ engines are interference designs: if the rubber timing belt breaks or a belt idler/tensioner pulley seizes, the pistons strike open valves and bend them, destroying the top end. From 1997 all USDM Subaru EJ engines (including the 2.2L SOHC) became interference after a piston/head redesign. Subaru specifies belt replacement at roughly 105,000 miles/105 months, but the belt gives no warning before it snaps, and on 25-30 year-old cars idler pulleys and tensioners are as likely to fail as the belt. Many high-mileage 1990s Imprezas are running on overdue belts, making this a leading cause of catastrophic engine loss on otherwise-sound cars. (Note: the earlier EJ18 and pre-1997 EJ22 SOHC are non-interference, so belt failure there is far less destructive.)

On the 1993-1999 Subaru Impreza, 1993-1999 Imprezas (GC8/GF8/GM sedan, coupe, and wagon) are highly prone to corrosion at the rear wheel arches, rocker panels, and the rear subframe/crossmember, particularly in salted-road climates. The outer quarter panel and wheel housing are joined with spot welds and foam adhesive that are not water-tight, and the overlapping inner-arch seams trap dirt and moisture in a hard-to-access pocket, so rust blooms from the inside out; by the time paint bubbles the damage underneath is usually extensive. The rear subframe and its mounting bolts also corrode; seized or sheared bolts complicate suspension work and can be an inspection (MOT/state safety) failure. This is age- and environment-driven wear that now affects the majority of surviving northern-climate cars.

On the 1993-1999 Subaru Impreza, automatic-transmission 1990s Imprezas use the 4EAT with an electronically managed transfer clutch (governed by the Duty C solenoid) to split torque to the rear wheels. When the Duty C solenoid or its control valve sticks/leaks, or the transfer clutch pack wears, the AWD stays partially locked and the car binds during low-speed tight turns, producing a grabbing, grumbling shudder and drivetrain resistance. It is often misdiagnosed as a suspension or tire problem. A quick test: installing the FWD fuse that isolates the transfer clutch will make the bind disappear if the solenoid/valve is the cause.

On the 1993-1999 Subaru Impreza, pressed-in front wheel bearings on these early Imprezas are a recurring wear item; the bearings were sized for the small factory 15-16 inch wheels, and larger aftermarket wheels, high mileage, or hard cornering accelerate failure. A failed bearing hums or roars proportional to road speed, often changing pitch under cornering load as weight shifts across the bearing. Because the bearing is pressed into the knuckle, DIY replacement effectively requires a hydraulic press, so most owners pay a shop or replace the whole knuckle/hub assembly.