Head Gasket Replacement: What Else to Replace

Replace the bolts that were stretched

Most engines that use an MLS head gasket clamp it with torque-to-yield bolts. Those bolts are tightened past their elastic limit on purpose. The second time they are torqued they do not clamp the same, and a new gasket leaks at the bore or at a coolant passage. Fel-Pro’s instructions for those engines say to install new bolts. A head bolt set is a separate catalog part from the head gasket and from the head set.

If the engine uses torque-to-angle bolts that the service information calls reusable, still measure them and look at the threads. Necked-down, rusty, or bottomed threads get replaced. Clean the threads in the block. Oil, sealant, or a dry thread changes the clamp load, so follow the Fel-Pro sheet for that part instead of a general “light oil on everything” habit. Do not torque a torque-to-yield bolt a second time because the first pass felt short.

Gaskets that come off with the head

The intake almost always has to loosen or come off. The old intake gasket will not reseal, and on a V engine the intake is often the coolant passage between the heads. A reused intake gasket is a common way to put coolant back into the oil after a careful head-gasket job. Replace the intake gasket or use the intake gaskets that came in the head set.

Exhaust manifold gaskets are heat-cycled and usually break when the manifold comes off. Replace them. Valve cover gaskets always come off; molded rubber Fel-Pro covers replace cork that has already taken a set. Valve stem seals are inexpensive while the head is on the bench, and worn seals are why a fresh head job smokes on the first startup. Many head sets include them. If this one does not, order the stem seals listed for the engine.

• Head bolts, when they are torque-to-yield or damaged.
• Intake manifold gasket, including the valley and any end seals.
• Exhaust manifold gaskets.
• Valve cover gaskets.
• Valve stem seals if the head set does not already include them.

Coolant, thermostat, and hoses

Combustion gas and oil contaminate the coolant. Drain it and fill with the coolant the engine calls for. Stop-leak products left in the system plug radiator tubes and heater cores, and they do not seal a head gasket. If a stuck thermostat is what overheated the engine, replace the thermostat. A hose that is soft, cracked, or swollen at the clamp will fail next to a new gasket and get blamed on the gasket.

Flush until the water runs clear if the oil was milky or a stop-leak product was poured in. Then fill with fresh coolant. Reusing the old coolant saves a few dollars and puts the contamination back on the new gasket.

The head has to be flat enough to seal

Check the head and the block with a straightedge before the new gasket goes on. An aluminum head that was driven while it was overheating is often warped past the spec for that engine. No Fel-Pro construction, MLS or composite, will pull it flat. Milling has to bring it back inside the spec, and the surface finish has to match the gasket you are installing. MLS wants the finer finish printed on its instruction sheet. A composite gasket tolerates a coarser finish and still needs a flat deck.

If the head is cracked between a seat and a coolant passage, or the block is eroded around a coolant hole, a gasket is the wrong repair. The part page cannot see that. The machine shop can.

What you can leave on the engine

The oil pan gasket, rear main seal, and timing cover gasket stay in place unless the procedure removes them or they are already leaking. That is why a head set exists separately from a full set. Opening the pan “while you are in there” on an engine that is still in the vehicle is a different job, and it needs its own gasket. Do not disturb a timing cover that the head-gasket procedure does not require; a new cover gasket means a new seal surface, a new crank seal on many engines, and another leak path if it is rushed.

Torque the head in the sequence and to the angle on the Fel-Pro sheet for that part number. A forum sequence for a similar engine is how a good gasket gets crushed on one corner and left loose on the other. After the engine reaches operating temperature, recheck only if that sheet tells you to. Many torque-to-yield procedures are one pass plus angle, with no re-torque.