Instructions for Changing a Chevrolet Head Gasket

The Silverado C1500 used several engines, including the ever-popular 5.7-liter engine. If the truck overheats, the head gaskets could leak, and once that happens, you must remove the heads. It is a complicated process, so you will need detailed instructions. If the truck overheats enough, it could cause one or both heads to warp. When replacing the gaskets, always send the heads to a machine shop to have them checked for wear and tear.

Tools

Several tools are required to complete this job. Though you can use hand tools, if you have air tools, the job goes much quicker.

Drain pan Tape and marker Set of wrenches Set of sockets Distributor wrench Set of line wrenches Screwdriver Breaker bar Torque wrench

Preparation

Locate the relay box near the driver’s side fender well. Using the diagram on the underside of the cover, locate the fuel pump relay. Remove the relay – you should be able to pull it out, using your fingers. Crank the engine over five or six times to relieve the fuel pressure. If the engine starts, let it run until it quits (because you took the fuel pump relay out, this means the fuel pump doesn’t come on, and it only runs until it uses up the fuel already in the fuel lines).

Disconnect the negative battery cable and set it aside. Make sure it does not touch metal. Slide the drain pan under the radiator petcock. If the engine is not cool, wait before proceeding. When the cooling system is warm or hot, it is under pressure. Removing the radiator cap or opening the petcock could burn you.

Open the petcock and allow the coolant to drain. If you remove the radiator cap, the coolant will drain faster. Discard the antifreeze in an appropriate manner. Not only is it bad for the environment to pour it on the ground, but it has a sweet taste that attracts animals. Antifreeze is poisonous to animals and will cause immediate death.

Remove the Intake Manifold

Label all the wires and vacuum hoses on the intake manifold. Loosen the clamps on the upper radiator hose at the radiator and the thermostat housing on the engine. Pull the hose off the radiator and the thermostat housing and remove it from the engine compartment.

Remove the throttle cables from the throttle body and set them aside. Match the distributor base to the intake manifold. Match the cap to the distributor base. Label the spark plug wires. Label, then unplug the wiring on the distributor. Pull the wires off the spark plugs, but leave them on the distributor. Remove the distributor hold down bolt, using the distributor wrench. Lift the distributor straight out of the engine.

Loosen the clamps on the heater hose and coolant bypass hose at the intake manifold then pull the hoses off the manifold. Unplug the wiring harness connector on the EGR valve, then remove the EGR valve, using the appropriate socket.

Disconnect the fuel pressure and return lines from the intake manifold, using the appropriate line wrenches. Remove the transmission oil level indicator and tube, using a wrench. Remove the EGR tube, its clamp and the bolt, using a socket. Loosen the clamps on the PCV valve and vacuum hoses, then pull them off the intake manifold.

Unplug the wiring harness connector for the air compressor, then unbolt the air compressor from the engine. Do not remove the high- and low-pressure lines on the compressor. Set the compressor out of the way, taking care to not kink the lines. Loosen the compressor-mounting bracket, using a socket, but do not remove it – simply slide it forward. Remove the power brake vacuum hose.

Mark the intake manifold bolts so you know where they go and in which order to torque them. Starting on the driver’s side, mark the bolts with the following numbers, from front to rear: 10, 9, 3, 2, 7, 8. The bolts are in groups of two. Mark the passenger side bolts, working from front to rear with the following numbers: 12, 11, 4, 1, 5, 6.

Remove the bolts and the intake manifold. Clean the gasket-mating surfaces of the intake and the lifter galley with a plastic scraper and rags, taking care not to drop any gasket material into the lifter galley.

Right Cylinder Head

Unplug the alternator wiring harness connector. Remove the power wire from the alternator, using the appropriate wrench. Put the nut back onto the stud, so you don’t lose it. Remove the alternator from the vehicle.

Remove the ground strap at the rear of the right cylinder head. Remove the oil dipstick tube. Remove the spark plug wire brackets from the rear of the head.

Left Cylinder Head

Unplug the coolant sensor wire harness and remove the wiring harness brackets at the rear of the head.

For Both Heads

Remove the valve covers. Loosen the rocker arm nuts enough to pivot the rocker arms. Lift the pushrods out of the engine, one at a time. Mark each pushrod – they must be reinstalled in their original positions.

Number the cylinder head bolts in the following manner. If you are looking down at the head, at the center of the head, you will notice there are three rows of bolts. Two rows are in the center of the head and the third row is at the bottom of the head. Number the top row with the following numbers: 13, 5, 2, 10. Number the second row with the following numbers: 17, 9, 1, 6, 14. Number the lower third row with the following numbers: 16, 12, 8, 4, 3, 7, 11, 15.

Starting with 17, remove the bolts in descending numerical order, using a breaker bar. Lift the head off the engine. Clean the gasket mating surfaces of the head and the engine with a plastic scraper and rags.

Send the heads out to the machine shop to have them checked for any warping.

Installing the Cylinder Heads

Before you change a head gasket on a 1998 Silverado, c oat the steel gasket on both sides with sealer. If you are using a composition gasket, do not use sealer. Position the head gasket on the engine with the word “Head” up. Clean the bolts, then apply sealer to the threads. Insert the bolts into their proper bolt holes and tighten them hand tight.

The bolts must be tighten in stages. Starting with the bolt No. 1, tighten them in ascending order to 22 foot-pounds of torque.

Tighten the short bolts (3, 4, 7, 8, 11, 12, 15, 16) another 55 degrees, in ascending order.

Tighten the medium bolts (14, 17) another 65 degrees.

Tighten the long bolts (1, 2, 5, 6, 9, 10, 13) another 75 degrees.

Reinstall the pushrods in their original position. Pivot the rocker arms onto the pushrods and tighten the bolts.

Reinstall the valve covers. Reattach the spark plug wires to the spark plugs. Reinstall the rest of the parts for whichever head you are working on in reverse order of removal.

Reinstalling the Intake Manifold

Position the intake manifold gaskets with the port blocking plates facing the rear of the engine. If you purchased factory gaskets when you decided to change a head gasket on a 98 Silverado , you should be able to see “This Side Up” on the gasket. Some aftermarket gaskets may also be marked accordingly.

Place a 5mm bead of RTV silicone on the front and rear sealing surfaces of the engine block. Extend the sealer about ½ inch onto the heads. Allow the RTV to skin over – when you touch it, it should not stick to your finger. Position the intake manifold onto the engine without disturbing the gaskets.

Apply sealer to the intake manifold bolts, then insert and tighten them by hand in their appropriate places as marked earlier. Staring with bolt No. 1 and working in an ascending order, tighten the bolts to 71 inch-pounds of torque. On the second pass, tighten the bolts in ascending order to 106 inch-pounds of torque. On the third and final pass, tighten the bolts in ascending order to 11 foot-pounds of torque.

Reconnect the wiring harnesses and brackets to the manifold. Reinstall the power brake vacuum tube. Reinstall the PCV valve, PCV valve hose, EGR tube, clamp and bolt, and the transmission oil level indicator and tube.

Reinstall the valve covers. Reconnect the wiring harness connectors, vacuum lines and throttle cable. Reinstall the rest of the parts in reverse order of removal. Close the radiator petcock. Fill the radiator with the proper mixture of coolant – see your owner’s manual for the specific mixture for your region. Reconnect the negative battery cable.

Leave the radiator cap off. Start the engine and check for leaks. Allow the engine to come to operating temperature. Once it does, the coolant will lower in the radiator. Top off the coolant. Reinstall the radiator cap.

Tip

You do not have to change both head gaskets if only one is bad. When you read the instructions on how do you change a head gasket on a 98 Silverado, you will see that steps for both heads are included. The left and right cylinder heads each have certain instructions to get down to the head, but after that, the instructions are the same for both sides. Follow the instructions for whichever side you are replacing, then go to the instructions for both heads to complete the process.


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