How do I replace my GM V6 Intake Gaskets?

IntakeIntake gaskets can be a very costly failure if you do not service them immediately upon finding them worn.  The intake gaskets on GM 3.1 liter, 3.4 liter, and 3.8 liter are very well known for having troubles.  These are some vehicles that have intake gasket problems.  So if you have a vehicle with one of these engines in them, make sure that you ask your dealership about some of the updated gaskets and intake manifolds to help prevent the failure.

We will discuss how an intake gasket fails.  Generally the intake gasket fails so that you will have engine coolant leaking into the engine.  This is bad because a liquid is not only uncompressible and can hydro lock a motor but it does not mix with oil.  If you run the engine long enough with this leak then you will have a lack of lubrication because there will be water in your oil and water does not have the lubrication properties of engine oil.

Next we will discuss some of the symptoms a vehicle with leaking intake gaskets may exhibit.  It may lack power or just sound different.  A good indication is if your vehicle coolant level is going down and you don’t see any coolant leaking onto the driveway.  This is because it is going inside your engine.  It is best to remove the spark plugs and read them.  If you look at the plugs and they are white this is a good sign of coolant.

Also if your engine becomes locked up do not try to continue to start it.  This is because there is enough coolant in your cylinder that the piston cannot compress it.  If you continue to try to crank the engine you can cause severe engine damage.  It is a good idea to remove all of the spark plugs and clear the cylinders by cranking the engine.  We will now go into the procedure for replacing your intake gaskets.

The Procedure

  1. Park your vehicle.
  2. Allow for a couple days of work if needed due to parts being broken that may need to be replaced.
  3. Remove all of the spark plugs in the engine.  If you don’t have a spark plug socket this ATD1380 106Piece Socket Set should contain the correct socket and the sockets that you will need to do this job.
  4. With all of the spark plugs removed it is a good idea to crank the engine over.  WAIT BEFORE CRANKING THE ENGINE OVER DISABLE THE SPARK AND THE FUEL.  To disable the spark disconnect the connector on the coil.  To disable the fuel locate the fuse for either the fuel pump or the fuel injectors and remove this.  You can now safely crank the engine over to clear out any water inside.
  5. You are now ready to start the removal process.  The first thing to remove is the air cleaner tube.  You will have to disconnect the intake air temperature sensor and then loosen the clamp.  Set it aside.
  6. Next remove all of the sensors connected to the throttle body.  Move the connectors out of the way.
  7. Remove the vacuum lines attached to the throttle body.
  8. Remove the throttle and cruise control cables from the throttle body.  Remove the cruise cable by pushing the plastic piece until it pops off the throttle arm.  To remove the throttle cable, open the throttle all the way and hold the arm.  Then move cable out of the groove and slide the little pin out with the cable.  You can release the throttle.
  9. You now need to remove the cables from the throttle body.  To do this, use a flat blade screwdriver.  If you don’t have a flat blade screwdriver this ATD6265 8 pc Screwdriver Set contains a screwdriver that will work.  Use the blade to pry up on the little tab that is holding the cables in.  Then simply slide the cables up and out.  Do this for both.
  10. Remove the EGR shield out of the way it consists of two bolts.
  11. You are now ready to remove the injector connectors.  Simply push in on the metal clip and pull up on the connector.  Make sure to pull up on the connector and not on the wires otherwise you risk damaging the wires.  Remove all the injector connectors.
  12. Remove the EVAP Purge valve connectors and any other electrical connectors that are attached to the intake manifold.
  13. Remove any brackets that look like they are going to be in the way for the intake removal.
  14. Now all that is left should be to remove the fuel rail.  To do this you will want to take off the cap on the regulator.  Then take a screwdriver and rags and gently depress the Schrader valve.  Fuel will come out that is why you have the rag handy.  Make sure to use extreme caution at this point.
  15. Remove the bolts holding the fuel rail in place.
  16. You will then need to remove the two fuel lines connected to the fuel rail.  Simply squeeze in on the plastic tabs and pull up.
  17. Now you can gently pull up on the fuel rail.  The injectors should come out with the fuel rail.  YOU HAVE TO BUY NEW INJECTOR O-RINGS FOR THE BOTTOM OF EACH INJECTOR!
  18. Remove all of the bolts holding the intake manifold in place.  Consult a service manual for the specific locations of your bolts and the number of bolts.
  19. With all of the bolts removed you will be able to pull the intake manifold off.  This is the upper intake manifold and on some vehicles specifically the GM 3.8 liter engines it needs to be replaced with new intake gaskets.  It is plastic on the 3.8 liter engine and warps.  Consult your local shop to see what needs to be done.
  20. Since you have the vehicle apart this far it is also a good idea to remove the lower intake manifold.  To do so simply remove the bolts holding it in place.
  21. With the lower intake manifold removed you will want to place rags in each port on the cylinder heads and rags in the valley to prevent you from accidentally dropping anything in either of those places.
  22. Now comes the time consuming part.  You will need a can of brake cleaner and a gasket scraper such as this ATD8560 3pc Scraper Set.  Use the brake cleaner and the scrapers to remove any and all gasket material.  Take care to not scrape any of the material into the engine.  Also don’t gouge any grooves into the aluminum this could cause leaks.  On the plastic intake manifolds you don’t have to scrape you simply have to either get the new gaskets or a new intake manifold.
  23. With everything all clean and dry it is time to install the new intake gaskets.  Start with the lower intake gaskets.  They will come with instructions on if you need to place silicone at the corners of the gasket or not so follow the instructions.
  24. Set your lower intake manifold in place.
  25. You will now need to look up the torque on the bolts.  You will also need to know if they need some kind of thread locking compound or not applied to the threads.
  26. With the torque and what should be applied to the threads you can start threading the bolts in by hand.  Get them all finger tight.
  27. It is now time to torque them.  There is a certain torque procedure for your specific vehicle consult the manual for it.  Also you will need to know how many torque stages you will need.  Torque the bolts, if you don’t have a torque wrench this ATD100M Torque Wrench will work.
  28. Next you will need the same information for the upper intake manifold.
  29. Set the gaskets in place and the upper intake manifold.
  30. Follow the torque procedure and use your torque wrench to torque the bolts to the manufacturers specifications.
  31. Now you are ready to reinstall the fuel rail.  WAIT BEFORE REINSTALLING THE FUEL RAIL YOU WILL NEED TO INSTALL NEW O RINGS ON THE BOTTOM OF EACH INJECTOR.  Then apply silicone based grease in a thin film to the injector O-ring.
  32. Slide the fuel rail in making sure that all of the injectors are seated in place.  Torque down the bolts.
  33. Reinstall the fuel line connections.
  34. Now simply reverse the procedure.
  35. When you are finished you will want to replace the spark plugs with new ones.  Your old spark plugs will be coolant fouled and should be replaced.
  36. With the new spark plugs you will also want to change your oil.  Your current oil will be full of coolant which is not a good thing.  So change the oil and filter.
  37. You can now fill the radiator.  Fill it with a mix of Dexcool and water at a 50/50 mixture.
  38. Start the vehicle and allow it to run.  You will have to bleed the air from the cooling system so open the bleeder valve located on either a heater hose or the thermostat housing.  Once coolant starts to come out of the bleeder valve you can close the valve.
  39. Shut the vehicle off and wait for it to cool.  If you don’t wait you can be severely burned.  Once the vehicle is cooled off you can remove the radiator cap.  Top off the radiator.
  40. You will also want to fill the overflow tank to the correct level.
  41. Now you can test drive your vehicle.  Take it on a good long test drive to insure that you don’t have any overheating.
  42. After your test drive check your oil level and look at the oil it should be black and not look milky.  If it is milky you still have an intake gasket leaking.
  43. You will also want to check your coolant rating.  To do so use a refractometer such as this ATD3705 Coolant-Battery Refractometer.

You just finished replacing intake manifold gaskets on your GM 3.1 liter, 3.4 liter, or 3.8 liter engine.  Your vehicle should now be trouble free and run much better.

Written by: Cody Mammenga an NDSCS Student

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