ASE P2 Test Preparation Guide: Gaskets

10/9/2009

By Larry Carley

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Sample Review Questions:
1. Which of the following must be removed to repair an intake manifold coolant or vacuum leak?
a. Cylinder head
b. Exhaust manifold
c. Intake manifold
d. Timing cover

2. Which of the following is NOT true about head gaskets?
a. Head gaskets can leak fuel
b. Head gaskets can leak coolant
c. Head gaskets can leak combustion pressure
d. Head gaskets can leak oil

3. Which of the following is NOT true about MLS head gaskets?
a. They must be retorqued 500 miles after being installed
b. They require very smooth and flat surfaces on the head and block to seal properly
c. They typically have 3 to 5 layers of steel
d. They are usually used with torque-to-yield (TTY) head bolts

4. If an engine has a leaky rear main oil seal, the oil would be leaking:
a.Near the harmonic balancer and crankshaft pulley
b. Near the flywheel
c. At the camshaft plugs
d. At the back of the valve covers

ANSWER KEY
1C, 2A, 3A, 4B

EXPLANATIONS:
1. The intake manifold gasket seals the intake manifold to the cylinder head. On many V6 and V8 engines, it also seals the intake manifold to the engine block. The gasket prevents air/vacuum leaks at the cylinder head intake ports, and coolant leaks at the cylinder head coolant ports. Coolant and vacuum leaks past the intake manifold gasket are common in high mileage engines. To replace the gasket, the intake manifold must be removed.

2. The head gasket seals the cylinder head to the engine block. This prevents coolant from leaking into the cylinders from the coolant jackets inside the block. The gasket also seals the cylinders so combustion pressure cannot leak externally or between cylinders. It also seals the oil passages between the block and head. A poor seal in any of these areas, or damage to the gasket can allow coolant, compression or oil leaks to occur. Head gaskets can be damaged by engine overheating, internal corrosion from worn out coolant, or improper installation (not torquing the bolts properly, not cleaning both mating surfaces, not having smooth, flat clean mating surfaces, or using a sealer on a coated gasket that does not require sealer).

3. Multi-layer steel (MLS) head gaskets are used on many late model engines to improve durability. They usually have 3 to 5 layers of steel, and are coated with a thin layer of rubber. No sealer is needed. To seal properly, MLS head gaskets require a very smooth, flat surface on the head and block. TTY head bolts are used with MLS head gaskets to assure even loading and to reduce cylinder distortion. TTY head bolts should not be reused. MLS head gaskets do not require re-torquing after the initial installation. Aftermarket MLS head gaskets are available for some engines that were originally equipped with ordinary head gaskets. An MLS gasket may be recommended to prevent premature gasket failure in a “problem” application.

4. Lip-style oil seals are used a the front and rear of the crankshaft to seal the engine. A worn rear main oil seal can allow oil leaks near the flywheel at the back of the engine. A bad front oil seal can leak oil near the crank pulley. Replacing a one-piece rear main oil seal requires separating the engine and transmission, and removing the flywheel.

Crankshaft oil seals must have a smooth, polished surface on the crank. If the surface of the crank is rough or worn, it can damage a new seal. A simple fix for this is to slip a repair sleeve over the end of the crank when the new seal is installed.

Camshaft oil plugs in an overhead cam (OHC) engine can leak oil at the back of the cylinder head. Oil leaks on the sides of the engine are most often due to old, cracked or damaged valve cover gaskets.