Diagnosis and Service Procedures
DIAGNOSISNOTICE: ONE OR MORE OF THE FOLLOWING FOUR (4) CONDITIONS LISTED BELOW MAY INDICATE A FAILED HEAD GASKET.
The following inspections may be performed to verify that there is a concern with the head gasket.
1. Confirm that there is coolant loss with no external leaks.
2. Check for bubbling in the coolant recovery or surge tank.
3. White smoke from exhaust system WHEN VEHICLE IS AT NORMAL OPERATING TEMPERATURE.
4. Remove spark plugs from a cool engine, refer to Section 6D4.
^ Inspect cylinder by looking through the spark plug hole. Water or coolant in the cylinder or a washed (clean) piston may mean there is a concern with the head gasket.
^ Remove ECM fuse and crank engine with spark plugs removed. Water or coolant vapor coming out of the spark plug hole may mean there is a concern with the head gasket.
^ Inspect spark plugs. Green contamination may indicate an internal coolant leak.
5. If steps 1 through 4 give no indication of a head gasket concern, fill the coolant recovery or surge tank. Mark and date the tank at the coolant level. Return vehicle to the owner. Ask the customer not to add any coolant to the system and monitor the coolant level. Have the customer return the vehicle to the dealership if the coolant level is low.
IMPORTANT: Condensation in the oil does not necessarily indicate a head gasket concern if there is no coolant loss. Some condensation in the oil may be considered normal.
SERVICE PROCEDURE
NOTICE: THIS SERVICE PROCEDURE SUPERSEDES ALL PREVIOUS SERVICE BULLETINS AND INSTRUCTION SHEETS FOUND IN THE PARTS KITS.
1. Completely drain the cooling system.
IMPORTANT: The cylinder block, head, radiator and heater core must be completely drained of coolant since the old coolant will be contaminated with combustion residue. Refer to the appropriate section of your service manual for draining procedure.
2. Remove the cylinder bead. Refer to the appropriate service manual section.
3. Inspect the timing chain tensioner shoe, refer to Figure 1.
IMPORTANT: On 1988 vehicles, also check the thickness of the backing plate. If the thickness is 2 mm (0.079 in.), replace the tensioner shoe and stud with GM Kit Part No. 12340864. The new tensioner shoe backing plate will be 3.7 mm (0.146 in.) thick, refer to Figure 1. GM P/N 24570357 will be an updated chain with smooth edges that will reduce tensioner shoe wear.
4. If the tensioner shoe is broken and the chain is worn from contacting the metal surface, use GM kit P/N 12340864 to replace the tensioner shoe and stud. P/N 24570357 to replace the chain and P/N 24570356 to replace the tensioner.
5. Disassemble, clean and inspect the tensioner assembly. Be sure to pay special attention to the oil feed and drain holes, refer to Figure 2. Make sure the oil holes are free of dirt so they will allow proper oil flow. If there is varnish in the tensioner bore or on the plunger that may cause the plunger to stick in the bore, LIGHTLY polish the plunger or bore with SCOTCH BRITE or equivalent. Do not use any other method or technique to clean the plunger or bore. Smooth surfaces will ensure the plunger will not stick in the tensioner assembly until it is needed for assembly in a location (ex. the parts cleaner) where dirt will not get into the oil holes. DO NOT USE ANY CLEANING MATERIAL OR METHOD THAT WILL REMOVE METAL FROM THE PLUNGER OR BORE.
6. Inspect the cylinder head bolts for damaged threads or for damaged heads caused by improper use of tools. Replace head bolts if necessary.
7. Thoroughly clean the cylinder head and block surfaces and check for flatness.
NOTICE: DO NOT USE POWERED ABRASIVE PADS TO CLEAN THE CYLINDER HEAD OR BLOCK SURFACES. A POWERED ABRASIVE PAD MAY DAMAGE THE CYLINDER HEAD AND BLOCK.
A. Carefully remove all gasket material. Use only a plastic or wood scraper. Use Loctite brand "Chisel Gasket Remover" (P/N 79040) or Permatex brand "Gasket Remover" (P/N 4MA), or equivalent. Do not use any other method or technique to remove gasket material.
IMPORTANT: NOT USE A TAP TO CLEAN THE HEAD BOLT HOLES.
B. Check cylinder head for flatness. Refer to service manual Section 6A7 for cylinder head checking procedure and specifications.
8. Inspect the cylinder head surface for corrosion or cracks. The combustion seal area will leave a "shadow" mark on the cylinder head (shaded area - Figure 3). If corrosion is evident outside of the outside diameter (OD) of the combustion seal area, (shaded area - Figure 3), the cylinder head may be reused.
9. Clean each head bolt seat boss on the cylinder head. Clean bolt holes in the cylinder block, refer to Figure 4. MAKE SURE THAT ALL PUDDLES OF OIL AND COOLANT HAVE BEEN REMOVED FROM BOLT HOLES OTHERWISE THE TIGHTENING SEQUENCE WILL NOT OBTAIN THE PROPER CLAMP LOAD BECAUSE OF HYDRA-STATIC LOCK. IF THE BOLT HOLES ARE NOT CLEANED THE HEAD GASKET MAY LEAK.
10. Replace the oil flow check valve (see Figure 5) in 1988-89 model year vehicles. Refer to the applicable 1991 model year service manual. The check valve does not need to be replaced in 1990 or newer vehicles or those vehicles where the check valve has been previously replaced.
IMPORTANT: To determine if the check valve has been previously replaced on 1988-89 vehicles, shine a flashlight into the oil check valve. If there are three dimples immediately above the check ball, it is the new style oil flow valve and should not be replaced (see Figure 5).
11. Apply clean engine oil SPARINGLY to the threads and the bottom side of the flange of the bolt (see Figure 6).
NOTICE: The following tightening procedure must be used to assure gasket life. Failure to follow this procedure exactly may result in cylinder head gasket leakage.
12. Install and tighten cylinder head bolts to the N.m (lbs.ft.) specification in SEQUENCE. Refer to Step A in Figure 7 for the specification.
13. After completing Step 12 on all ten bolts, tighten all the cylinder head bolts an additional 90 degrees, indicated in Step B of Figure 7 in SEQUENCE using J 36660.
14. Replace thermostat.
15. Assemble the rest of the engine, refer to the appropriate service manual.
16. Change the engine oil and filter, being sure to use a PF 1225 oil filter, or equivalent.
17. Add two (2) engine cooling system sealer pellets from package, P/N 03634621, to the cooling system.
18. Fill the cooling system. Use a mixture of water and coolant meeting GM specification 1825-M to get a protection level of -37 degrees C (-34 degrees F) to maintain sufficient engine cooling, freezing and corrosion protection. Do not use a mixture that has more than 70% anti-freeze in it.
^ 1988 Model Years
a. Disconnect heater inlet hose from engine coolant outlet.
b. Remove pressure cap from radiator and fill with coolant until coolant drains from the engine coolant outlet.
IMPORTANT: This process may take up to 15 minutes.
c. Reconnect heater hose to engine coolant outlet.
d. Start engine.
e. Continue to fill radiator as coolant level drops until the radiator hose at the radiator inlet is hot and coolant level in radiator becomes stable.
f. Fill radiator completely.
g. Install pressure cap.
h. Stop engine.
^ 1989-91 Model Years:
a. Remove the top radiator hose from the radiator prior to refilling the coolant.
b. Fill the coolant system until coolant appears at the radiator inlet.
c. Reinstall the top radiator hose to the radiator inlet and continue filling surge tank to the base of the filler neck.