Replacing the head gaskets on a Subaru 2.5 is a procedure that may be completed while the engine is still in the car. It is a challenging task that should be attempted only by someone with considerable mechanical skill and a full set of automotive service tools both metric and standard. Always wear safety glasses and gloves to protect yourself from caustic chemicals and gasoline. Always have a fire extinguisher handy.
Relieve the pressure in the fuel system by removing the gas cap, disconnecting the fuel pump relay and running the engine until it stops. Disconnect the negative battery cable. If your vehicle is before 2002 and it has the factory vehicle theft system, follow the instructions in the owner's manual to disable it or your radio will not function when you reconnect the battery. Drain the cooling system. Recover the coolant for reuse or recycling.
Remove the spark plugs, timing belt covers, belt, camshaft sprockets, camshafts and disconnect the exhaust manifolds (use penetrating oil to loosen the bolts if necessary). Remove the intake manifold and any other hoses, brackets or accessories that block access to the sides of the engine.
Loosen the cylinder head bolts in the reverse order for tightening. This is generally from the top center to the bottom center then an "X" pattern for the ends. Remove the heads and the old gasket material carefully. Place a clean shop towel in each cylinder to prevent debris contamination.
Use the acetone or lacquer thinner to clean the gasket mating surfaces. Carefully scrape any stuck material from the surfaces. They must be absolutely clean to seal properly. Install the new gasket onto the head locating dowels. Lubricate the head bolts with engine oil and install them finger tight.
Use the torque wrench and torque angle gauge to tighten the head bolts in the exact sequence outlined by the references. Over-tightening will strip the threads and improper sequence can warp the head.
