GM 5.7L intake manifold gasket

 

 

 

The GM 5.7L(and 5.0L which is virtually the same engine) intake manifold gasket is an extremely high failure item. Of the millions of cars and trucks sold with this engine, 99.9% will have an intake gasket leak at least once, and if the vehicle lasts more than 100,000 miles, it may leak two or three times. This means that every 5.0 or 5.7 liter GM car or truck that comes into your shop should be inspected for a leak.

 

Inspection

 

The most common area of failure is at the front of the engine, behind the alternator bracket or air conditioning bracket. Behind the alternator is not easily visible, so a small mirror and a flashlight will be needed to verify the leak unless it is very bad. You should be looking for oil, coolant, or a combination of both. If coolant is seen, a disclaimer must be attached to the ticket waiving the shop of any responsibility in the event that coolant also leaked into the crankcase and damaged the bearings, possibly resulting in future engine failure. Also 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. Although leaks at the front or more common, the rear of the intake will sometimes leak as well.

 

Disassembly

 

Begin the procedure by draining the coolant. Remove the air filter box lid and air intake boot with filter attached. Leave the bottom of the air filter box, as it makes an excellent tray for brackets and other larger pieces that will be removed from the engine. Next, remove the upper fan shroud (one of GM's best ideas), the fan clutch assembly, drive belt, and idler pulley. The water pump pulley doesn't have to be removed, but it does give a little more room to work later. Now remove the electrical connectors at the front of the engine and from the AC compressor. Release both of the cables at the throttle body and the throttle cable bracket. Unbolt the compressor and fold it over to the passenger side of the engine compartment and fold the throttle cable bracket over to the driver's side.

 

 

The alternator does not have to be removed, but again, it makes the job easier later (don't forget to disconnect the negative cable at the battery). Once the alternator is out of the way, inspect the coolant hose quick disconnect fitting behind it. If it does not appear to have been replaced in the last 6 months, you need to do it now. These fittings are made from an extremely cheap metal and break very easily. It is likely that it will break off in the intake when you try to remove it. A tool can be purchased on most tool trucks that can be hammered down into the broken fitting and twisted out (buy this tool before the fitting breaks). Now remove the other coolant hose from the water pump and fold it over to the side along with the hose from the quick disconnect and the AC compressor. Remove the upper radiator hose and the EGR fitting.

 

Getting into your work

 

At this point, the easiest way to proceed with the job is to climb up into the engine compartment and sit on the radiator support (careful not to catch the seat of your pants on the hood latch). Watch the placement of your feet so that you don't damage any of the components on either side of the engine. Many techs have found that the best position is the left foot on the alternator bracket and the right on the sector shaft. This places you in a position easily accessible to the engine and all components. Make sure to have your tool cart close by as well.

 

 

Now release the evap. hose from the valve on the passenger side of the intake. With a small screwdriver, press the white clip into the fitting(seen above), releasing the catch, and pull the hose off of the valve. Fold this hose over to the driver's side of the engine compartment. Now release all of the electrical connectors from the top of the engine and all of the clips that hold the wiring harness. Be extremely careful when removing and installing the large fuel injector connector in the center of the intake. If one of the pins is bent, that injector will not activate, causing a hard to diagnose misfire.

 

 

 

This is the fitting for the brake booster (above). To remove it, twist clockwise until it stops, and then pull up. Next, remove the PCV tube and set it aside, unbolt the bracket on the driver's side of the intake that holds the blue connector and move it to the side. Also unbolt the bracket behind it that supports part of the wiring harness and set it aside.

 

 

The bracket that routes over the passenger side of the distributor cap and bolts down over the coil is retained by three bolts. Two are at the top and are easily removed. The third is on the back side of the cylinder head and is not so easily removed. Here, you can choose which way you want to remove this bracket. Either it can be unbolted entirely and set aside, or you can remove the two nuts at the top and bend the bracket up and over the coil and distributor cap and out of the way. Both ways yield the same result, but the second is much faster. Now remove the coil and set it aside.

 

 

Note, in the picture above, that the spark plug wires on the driver's side of the cap are routed in the same order in the clip as they are on the cap. Remove them from the cap and remove the 13mm bolt holding the plug wire clip and the EGR tube bracket and pull them out of the way. The EGR tube should be flexible enough to bend it up and over the oil filler tube and rest it on the other side. If it feels like it may crack, however, remove the oil filler tube, and using a bungee cord, pull the EGR tube as far out of the way as you can without breaking it. Next remove the two torx screws holding the distributor cap on and set the cap over to the passenger side with the plug wires still attached.

 

Fuel line disconnect

 

 

Some techs like to disconnect the fuel lines from the top of the intake at the injector assembly and then flex the fuel lines out of the way. I find it easier to take the lines loose at the back of the intake. Simply remove the two 16mm fittings at the back next to the distributor. The easiest way to do this, due to the lack of room to swing a wrench, is to break them loose with a medium-length line wrench (be sure to hold the other side of the fitting when you do) and then run the nuts out by hand if possible, or a stubby wrench if they are too tight.

 

 

Be sure to mark the distributor

 

 

Now, clean off a portion of the base of the distributor and make a mark with liquid paper from the intake to distributor. Be as precise as you can, because the closer you get the two marks on re-assembly, the less time you will have to spend setting cam timing when the job is done. A mark also needs to be made at the rotor button. This is not as critical as the lower mark, but still needs to be as precise as possible. Once these marks are satisfactory, remove the distributor and set it aside. Plug the distributor hole with a rag so that nothing gets dropped down into the engine.

 

 

 

Next, using a bungee cord, pull the wiring harness up off the top of the intake. It needs to have several inches of clearance between it and the top of the intake for ease of removal and installation. Secure the bungee cord to the base of the passenger side windshield wiper arm.

 

 

AC and Power Steering Bracket

 

 

Next, remove the AC and power steering bracket. To do this, the three visible bolts and one nut must be removed. There is another nut down at the bottom of the bracket, usually covered in dirt and grime, and very hard to find the first time. Once these five fasteners have been removed, there is a sixth nut behind the power steering pump below the exhaust manifold on the drivers side. This nut only needs to be loosened, not removed. Now the bracket should slide forward and out of the way of the intake. It is your choice to either slide it along the stud, or to pull it all the way forwards and rest it on the bottom of the fan shroud.

 

 

 

 

 

Now remove the coolant hose between the water pump and the intake. If the clamp is in an accessible position, remove the hose from the intake. If it is not, remove it from the water pump, but once the intake is off, remove the hose from the intake(it can get in the way of setting the intake down properly if it is still attached). Inspect the hose for any damage. If the hose is aged or has any swollen areas, replace the hose.

 

 

 

Valve Cover

 

 

Bend the main harness bracket out of the way and remove the passengers side valve cover. It is not necessary to remove both valve covers.

 

 

 

 

Final steps before intake removal

 

Now the intake should be nearly ready to come off. Remove the eight bolts retaining it to the heads and, using a screwdriver or a small pry bar, pry up on the front of the intake to break the seal. Do not remove the bolts attaching the plastic upper intake plenum to the lower intake. With the 8 intake bolts removed and the gasket seal broken using a small prybar, the intake should lift off the heads with a minimum amount of effort.

 

 

 

Below you can see the split in the gasket that was allowing the coolant leak at the right front of the engine. This leak was external, but it is very possible that coolant was also leaking into the valley of the engine and mixing with oil. This can cause future engine problems even if the oil does not appear to be contaminated.

 

 

 

Surface preparation

 

 

The first thing to do once the intake is off, is to clean up any coolant that may have spilled into the lifter valley. Any that went into the oil pan will come out when the oil is drained later. Place some rags at the bottom of the lifter valley to catch any debris from the cleaning process. Begin by wiping off any loose particles and gasket material with a rag, then scraping the surface with a razor blade. Once the heads are fairly clean, use a die grinder with a medium grit bristle disc to finish prep the heads. Once all of the surface is clean, inspect around the coolant passages for signs of pitting. Usually an engine with cast iron cylinder heads has fewer problems with pitting than one with aluminum heads, but higher mileage vehicles may have some pits deep enough to need filling with silicone later.

The eight bolts that retain the intake will need to be cleaned up. Any debris on the threads will affect the torquing process and may cause a leak. Make sure that before they are re-installed, the bolt threads are clean and dry.

 

Now the intake manifold must be cleaned. Once again, wipe off any loose particles, then scrape with a razor blade (be careful not to gouge the surface) then use a very fine grit bristle disc (above) suitable for aluminum (the 3M aluminum discs are white, yellow works well for the heads). Be careful not apply too much pressure or stay in one place too long when cleaning the intake. The gaskets can only compensate for a very small amount of surface variation.

 

Never, ever use a disc such as the one below to clean engine parts. They are fine for rotors, but if used on the heads, you may as well throw a hand full of sand into the engine, and the aluminum intake would gouge extremely easily with this disc. The problem is that the grit is much too course for softer metals, and the compound is made almost entirely of silica. As it wears it throws off particles into the engine. If these particles then enter the oiling system, they will damage the bearings and cylinder walls.

 

 

 

Install the Gaskets

 

 

Once both of the surfaces have been thoroughly cleaned and wiped with solvent, apply a thick bead of silicone to both surfaces of the block, making sure to extend the beads up about inch onto the heads. Don't forget, if you had pitting around the coolant passages to fill it with a small amount of silicone. Now place the gaskets down on the heads, making sure that the pins on the back of the gasket are pressed into the holes on the cylinder head. Apply another small dab of silicone to each corner of the gaskets to complete the seal. Don't forget to remove the rags from the lifter valley.

When all of this has been done, the intake is ready to be re-installed. Note that the fuel lines will have to be put in their corresponding fittings before the intake can be set down. Also make sure to set it straight down, and not slide it to line up the bolt holes. Once the intake is properly located, apply a small amount of thread locker to each of the bolts before you install them. This is necessary to keep the bolts from backing out due to the light torque required. Torque the bolts to 11 ft. lbs., making several passes, increasing the torque each time until you reach 11 ft. lbs. These gaskets are designed to seal at a low torque. Using proper torque specs if very critical on this job. When finished, make at least one more pass around to ensure that all of the bolts are at the specified torque. Once the intake is on, install the valve cover, torquing the bolts to 89 in. lbs.. At this point, put everything back in the reverse order that it was removed.

 

Conclusion

 

Once the engine is re-assembled, perform an oil change and fill up the coolant. Start the engine and check for leaks. Once the engine has warmed up, the cam timing needs to be set. Unfortunately, a timing light won't work, a scan tool with manufacturer specific capabilities must be used. Different scanners have different methods of doing this, but a few moments of searching should yield the section you need. Follow the on-screen instructions to adjust the timing.

It is nearly impossible to properly complete this job properly in the 4.1 hours alloted in most labor manuals. It is recommended that a minimum of 5.5 hours be charged for this job, in addition to any extra repairs being performed at the same time (thermostat, tune up, etc.). Once you have done two or three of these, they become much easier, and are an excellent way to make bill hours for all the flat raters out there.

 

Adam Riggs

ASE certified technitian