GM 4.3L intake manifold gasket

 

 

The GM 4.3L intake manifold gasket is just like any other GM gasket: it leaks. This being said, it is very similar in procedure to the 5.7L found in many trucks and SUVs.

 

The most common area of gasket failure is at either side of the front of the engine. If the leak is on the passenger side, it may be harder to pinpoint since the alternator bracket obscures much of this area. A small mirror and a flashlight will be needed to verify the leak unless it is a heavy leak. You should be looking for oil, coolant, or a combination of both. If coolant is seen, a disclaimer should be attached to the ticket waiving the shop of any responsibility in the event that coolant has also leaked into the crankcase and damaged the bearings, possibly resulting in future engine failure. Even small amounts of coolant in the crankcase can mix with oil and cause future bearing failure. It is not always apparent that coolant is mixed with the oil by simply pulling out the dipstick and doing a visual inspection. Small amounts of coolant can mix with the oil and not be visually detectable. Often, the engine will run ok after repairs, but may return several months after the repairs with crank or bearing damage.

 

Also be sure to check for a leak at the rear of the engine. It can be seen with a mirror on top of the transmission bell housing, or in extreme cases, leaking down into the bell housing and out of the drain at the bottom of the torque converter shield.

Disassembly

 

 

 

Begin by draining the coolant and disconnecting the battery. Remove the air filter box and intake boot from the throttle body. Now remove the fan shroud, then the fan clutch and accessory drive belt.

 

Always use the proper tool for the job, as seen below. A fan clutch wrench and pulley holder are being used to break loose the large fan clutch nut from the water pump.

 

 

 

Next, remove the throttle and cruise control cables from the throttle body and remove the two brackets from the intake and set them aside near the master cylinder.

 

 

 

Disconnect the two electrical connectors from the AC compressor and remove the four bolts holding it to the bracket. Set the compressor assembly over to the passenger side of the engine compartment, as seen here. Ensure that the hoses are not kinked or stressed as this may cause a leak, especially in older vehicles.

 

 

 

Next, remove the idler pulley and alternator. Be careful when loosening the battery wire from the back of the alternator, as the stud may try to spin out of the housing. Hold the stud with a wrench as the nut is loosened to keep the battery wire from wrapping around the socket.

 

 

Now, the wiring harness that runs across the top of the engine must be relocated. Disconnect all of the electrical connections at the top of the engine (including the large fuel injection connector in the center of the intake, making sure that the retaining tabs and contact pins are not damaged upon removal) and fold the entire harness over to the passenger side of the engine compartment and retain it with a tie strap or bungee cord.

 

Take the upper radiator hose loose from the intake and fold it out of the way or remove the other end from the radiator. The vacuum hose to the brake booster must also be removed. To do this, grasp the plastic elbow where the brake booster hose enters the intake, depress the locking tab, and turn clock wise. There should be a slight detent, and then the elbow should pull up and out of the intake manifold. It may take some twisting back and forth and possible a penetrating oil before the plastic elbow will release. Be careful and do not tug so hard as to break the plastic elbow or intake.

 

 

 

The AC/power steering bracket must be loosened and pulled forward to access the front intake bolt. Start by loosening (don't take it all the way off) the nut behind the power steering pump as seen in the picture above.

 

 

Now remove the three bolts and two nuts on the front side of the power steering bracket. There is a hidden nut tucked under the bracket that must also be removed.

 

 

 

Once the AC/power steering bracket is loose, slide it forward along the stud until there is enough room to access the intake. In the picture below, the power steering bracket has been moved completely off of the stud. This is not really necessary. All that needs to be done is the bracket needs to be slid forward several inches.

 

 

With the brackets removed, the leak can be seen easily.

 

 

The coolant was leaking out of the passenger side coolant passage, and running along the top of the block over to the driver side of the engine.

 

 

 

Now that the front of the engine is accessible, proceed by removing the EGR tube and bracket. The EGR nut at the front of the intake is 7/8. Once loose, try to gently flex the tube over to the side. If it shows signs that it may break, stop and have a helper hold it when removing and installing the intake manifold. Also remove the PCV valve and tube.

 

Remove the two heater hoses, one from the fitting on the intake and the other from the tube at the water pump. Also, remove the intake side of the bypass hose from the water pump to intake and fold it out of the way. The coil bracket does not have to be removed, but the rest of the job is much easier with it out of the way. Remove the evaporative emissions line from the solenoid valve at the right rear of the intake by pushing down on the white clip and gently pulling on the line.

 

 

The distributor must be removed since it passes through the intake manifold. The easiest way to do this is first, ensure that the plug wires coming from the drivers side of the engine are lined up in the loom in the same order that they are on the cap. Pull them off of the distributor cap and, along with the EGR tube if possible, pull them out of the way. Remove the two small torx screws holding the distributor cap on and fold it and the remaining wires over to the passenger's side of the engine compartment. Do not remove the plug wires from the passengers side of the cap. On this particular year, the distributor is not adjustable, so only the rotor to housing relation must be marked. Marking the distributor location with white out will ensure it is reinstalled correctly.

 

Once the rotor has been marked to the housing, remove the hold down bolt and pull the distributor out of the engine. Stuff a rag in the distributor hole to keep any tools or parts out of the engine.

 

 

Using a stubby 16mm wrench, loosen the fuel lines at the rear of the engine as seen below. If the lines are excessively tight, you will need to use two wrenches. One to hold the line and the other to loosen the nut. Typically, however, fuel line bracket will hold the lines tight enough to allow you to loosen the lines without using two wrenches.

 

 

 

Remove the other end of the evap line that was previously disconnected and set it aside.

 

 

Time to Remove the Intake

 

The engine should look something like this now(below). All wires and hoses are out of the way and everything is disconnected from the intake manifold. Now remove the eight intake bolts (the right rear bolt is hard to access with a socket due to the large wiring harness running near it) and the intake manifold.

 

 

Once the intake has been removed, inspect the gaskets for any signs of breakage or leaking as seen below. This picture also shows how easily the coolant can enter the valley of the engine and mix with the engine oil when the intake gasket leaks.

 

 

Surface preparation

 

Before beginning the gasket removal, place several clean rags in the lifter valley to minimize the amount of particles that enter the crankcase. Once the gaskets have been removed, use a rag to wipe off the loose pieces on the gasketing surface and surrounding areas. Next, use a razor blade to scrape off the next layer. Finally, using a 3M bristle disc, lightly prep the surface of the head, paying close attention to the areas around the coolant passages.

 

DO NOT use this style of prep disc. (seen below) The silicates used in it will break apart and enter the crankcase which can damage the bearings. This type disc can also gouge the aluminum intake manifold and destroy the sealing surface.

 

 

Instead, use a bristle-type disc, as shown below. They are available on most tool trucks and at most parts stores.

 

 

Once all particulate matter has been removed from the gasketing surface on both the head and the manifold, inspect for corrosion around the coolant passages. If any is found, it must be coated with silicone before installing the intake. The gaskets on this engine are designed to seal without the use of silicone around the coolant passages. Do not use silicon UNLESS pitting and corrosion are severe enough to keep the gasket from sealing such as with the picture below.

 

 

Clean the threads of the intake bolts with a wire brush and some brake cleaner to minimize the chance that material on the threads will falsify the torque readings. Bolt torque is VERY important on this style intake gasket. These gaskets are designed to use a very low torque. Dirty bolt threads will cause inaccurate torque readings when tightening.

 

 

Re-installation

 

 

Once all surfaces are clean and ready, apply a bead of silicone to the surface of the block between the cylinder heads at the front and rear of the engine. This bead should be about as wide as the surface that it is on, and approximately inch high. Extend this bead at either end up onto the surface of the head by about inch. At this time, ensure that any pitting on the cylinder head and intake is filled with silicone as well. Place the intake gaskets on the head surface making sure that the pins on the back enter the holes on the head. Now place a small dab of silicone on each corner of the intake gasket where it meets the silicone from the block to complete the seal. A drop of thread locker is needed on the intake bolts to ensure that they do not back off due to the low clamping forces necessitated by the gasket construction.

When re-installing the manifold, ensure that the fuel lines enter the connection at the back of the engine. Place the intake straight down on the engine. If at first the bolt holes do not line up, pick the intake up and reposition it. DO NOT slide it as this will push the silicone away from the block. Start all eight of the intake bolts in the heads, then gently snug them all down uniformly. Start the torque procedure with about 89 inch lbs., starting in the center and moving outwards in a circle. Next, torque to about 106 inch lbs. in the same pattern. Finally, torque all bolts to 11 ft lbs. Do this step several times to ensure that all bolts are evenly tightened.

Once the torque process is complete, reverse the order of disassembly to complete the repair. Do not forget to change the oil and filter to minimize the chance of engine damage. Fill the engine with coolant, re-connect the battery and start the engine. As it warms up, inspect for leaks or any other problems. Test drive and re-check for leaks. This repair is not as difficult as it may sound, but is indeed time consuming the first few times. Allow plenty of time to ensure that mistakes are not made and nothing is overlooked. If any one step is left out or forgotten, the vehicle will almost certainly come back with a check engine light on or a leak. Do it right the first time.

 

Adam Riggs

ASE Certified Master Technician