Parts for your 2004 Subaru Impreza-Head gasket

2004 Subaru Impreza head gasket — what it does and when to sort it

Yes, a head gasket is absolutely used on the 2004 Subaru Impreza. Every EJ-series boxer engine fitted to this model year (including the 2.0 WRX EJ205, 2.5 NA EJ251/253 and performance variants) runs a head gasket on each bank. This is documented in the 2004 Subaru Impreza Factory Service Manual, the Subaru parts catalogue listings for left/right cylinder head gaskets, and supported by Subaru Technical Service Bulletins about external coolant seepage on Phase II 2.5-litre engines and the recommended Cooling System Conditioner (for example, TSB 09-36-03 and later revisions).

On a flat-four, there are two cylinder heads and therefore two head gaskets. Their job is to seal combustion pressure, coolant and oil passages between the block and heads. Turbo models typically use multi-layer steel (MLS) gaskets from factory, while many naturally aspirated 2.5s originally used a composite style that’s more prone to external coolant weeps as the kilometres rack up.

Owners of a 2004 Impreza should keep an eye on early warning signs so a small issue doesn’t turn into a bigger drama:

• Sweet smell or light coolant misting at the head-to-block seam
• Unexplained coolant loss, bubbles in the overflow, or system pressurising when cold
• Milky residue under the oil cap, rough cold starts, or overheating under load

When replacement is due, it’s smart to do both sides together. The heads should be pressure-tested and skimmed if needed, the cooling system fully flushed, and fresh thermostat, radiator cap and hoses considered. Many workshops in AU/NZ prefer the updated OEM MLS-style gaskets (or quality equivalents), fresh head bolts, and meticulous torque-angle procedures from the factory manual. Because it’s a timing-belt job on most variants, it’s cost-effective to pair the work with a timing belt, idlers and water pump if they’re due—saving a second round of labour down the track.

For ongoing care, stick to correct coolant spec and change intervals, use distilled/deionised water where appropriate, and keep the cooling fans and radiator clean—especially if the car sees beach runs or country gravel. Subaru’s Cooling System Conditioner was factory-endorsed for minor external seepage on certain 2.5 NA engines