An engine's intake manifold operates to direct the air/fuel mixture into the cylinder heads, which in turn distribute the mixture into the combustion chambers. In addition to the air/fuel mixture, antifreeze also flows through the intake manifold. Underneath the intake manifold is an area called the "valley," which contains the valve lifters. Oil constantly circulates through the valley to keep the valve lifters lubricated. On occasion, the bolts used to secure the intake manifold to the engine break when turned. This is particularly problematic with old bolts. Once one or more bolts have broken, the risk of the various engine fluids commingling increases, which can seriously damage the engine. Thankfully, a broken intake manifold bolt is easier to remove than some other bolts, particularly broken cylinder head bolts, but the intake manifold must still be removed.
Disconnect the upper radiator hose and the water pump hose from the intake manifold. Both hoses attach to the intake manifold with a hose clamp. Loosen the screw on each clamp with a screwdriver, then pull both hoses off of the intake manifold.
Remove the distributor, if the distributor enters the engine through the top of the intake manifold. To remove the distributor, pull each spark plug wire off of the distributor cap, then remove the distributor's single hold-down bolt with a wrench. The hold-down bolt is located underneath the distributor where the distributor meets the intake manifold. Once the hold-down bolt has been removed, pull the distributor straight up to remove it.
Remove the valve covers from the cylinder heads with a wrench. Each valve cover attaches to its cylinder head with several retaining bolts located on the valve cover's lip. Remove the retaining bolts, then pull the valve covers off of the heads.
Remove the intake manifold from the engine with a wrench. Like the valve covers, the intake manifold uses several bolts to attach to the cylinder heads. Once the intact bolts have been removed, lift the intake manifold off of the engine to expose the broken manifold bolt(s).
Spray the broken bolt(s) with an aerosol lubricant, such as WD-40, then allow at least 30 minutes to pass.
Remove the broken intake manifold bolt(s). Use a large pair of locking pliers to grasp the broken bolt. The pliers should be adjusted to maximize the gripping power of the pliers by turning the adjustment screw on the bottom of the pliers in a clockwise direction. Grasp the broken bolt with the jaws of the pliers as close to the base of the bolt as possible. If the bolt's threads are visible, grasp the threads. Slowly turn the bolt in a steady motion in a counterclockwise direction until the bolt breaks free, then unscrew the bolt to remove it.
