1999 Subaru Forester Problems: 5 Known Issues

On the 1998-2010 Subaru Forester EJ25, the EJ25 2.5L horizontally-opposed engine in 1998-2010 Foresters is notorious for external head gasket failure. Unlike typical blown head gaskets that cause overheating, the Subaru EJ25 gaskets fail externally, leaking coolant and oil down the sides of the engine. The failure is caused by the gasket material (composite) breaking down over time, combined with the horizontal orientation placing uneven stress on the gaskets. This is widely considered the most common and well-documented Subaru defect.

On the 1998-2010 Subaru Forester, the EJ-series front-mounted oil pump has a rotor cover (backing plate) held on by five small screws installed without thread locker at the factory. On high-mileage engines these screws routinely work loose. Pressurized oil then escapes past the rotor cover into the pump body behind the front crankshaft seal, which pushes the seal partly out of its bore and produces what looks like a classic 'front main seal leak' — often re-leaking within months of a seal-only repair. The same internal leak bleeds pump volume and can show up as low oil pressure, a flickering oil light at hot idle, or lifter/HLA tick. Technicians who have opened many EJ pumps report finding loose screws on nearly every one.

On the 1998-2005 Subaru Forester, the single knock sensor bolted to the top of the EJ block on SF- and early SG-generation Foresters has a brittle plastic/resin housing that cracks after years of heat cycling directly on the block. Once cracked, the piezo element's circuit reads out of range and the ECU sets P0325. The car keeps running, but the ECU falls back to a conservative safe ignition map: owners report noticeably reduced power, sluggish throttle response and a measurable drop in fuel economy. The failure is common enough that many independent shops replace the sensor on any high-mileage EJ Forester showing that code without further diagnosis. A secondary cause is the sensor wiring harness chafing or the connector corroding, so the harness should be inspected before condemning the sensor.

On the 1998-2010 Subaru Forester, on automatic-transmission Foresters with the 4EAT gearbox, all-wheel drive is managed by an electronically controlled multi-plate transfer (MPT) clutch on the tail of the transmission, modulated by the 'Duty C' solenoid. When the solenoid sticks or the clutch pack glazes, the clutch stays fully applied on dry pavement and the car binds, shudders and hops through slow tight turns — parking lots, U-turns, driveways. Mismatched tire circumference (one new tire, or uneven wear) accelerates it by forcing the clutch to slip constantly. The diagnostic that confirms it is inserting the FWD fuse in the underhood holder: if the binding disappears with the transfer clutch de-energized, the fault is in the AWD path, not the front axles or brakes.

On the 1998-2008 Subaru Forester, the rear differential on SF and SG Foresters hangs on rubber bushings — a large front mount bushing plus rear outrigger bushings tying the diff nose and carrier to the body. The rubber dry-rots and cracks with age, letting the differential rotate and move vertically before it transmits torque. Owners describe the classic 'Subaru diff clunk': a hard thump when shifting from reverse to drive, a bang on hard throttle application or fast shifts in the manual cars, and a general clunk from the rear over bumps. In advanced cases the diff bottoms the subframe against the body. It is frequently misdiagnosed as a failing rear wheel bearing, a bad CV joint, or a transmission mount, and the tell is that the noise tracks torque reversal rather than road speed.