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Replacing the 3.5 V6 Intake Manifold Gasket

Click here for other issues which can cause rough idling on the 3.5 liter engine

3.5L Intake Manifold Gasket Replacement Procedure

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Why do it?

The original gasket tends to crack and leak at about 50 to 75K miles. This creates a masive vacuum leak and the engine will run rough and skips . It only needs to be replaced when it leaks but it happens often. I wrote these instructions for a person who found me on the board so I wrote them like an article and figured you could use them.

Parts

Intake Manifold gaskets(lower)

  • Air plenum gasket (upper intake)
  • 2 - Fuel rail gaskets
  • Tube of RTV silicone

Process

  1. Start the engine and remove the fuel pump relay (while the engine is running) to relieve any fuel pressure from the system
  2. Drain the cooling system by opening the drain 1 turn only
  3. Remove the upper radiator hose
  4. Remove the engine cover from the top of the intake plenum
  5. Disconnect the AIS motor , TPS , and MAP sensors electrical connectors
  6. Remove the two 15mm head bolts on either side of the intake plenum that attach it to the stiffening brackets
  7. Disconnect the vacuum lines from both ends of the intake plenum and from the throttle body's
  8. Remove the fresh air intake ducts from the throttle body's
  9. Remove the PCV hose from the PCV valve
  10. Remove the EGR tube mounting bolts that attach it to the intake plenum (you can leave the tube connected to the EGR valve)
  11. Remove the center attaching bolts holding the air plenum to the lower intake manifold
  12. Remove the air charge temperature sensor electrical connector and the MTV vacuum hose (both located towards the centerline of the air plenum)
  13. While leaving the throttle cables connected you can lay the air plenum on the top of the drivers side fender (be sure to use a fender cover)
  14. Disconnect the vacuum line from the fuel pressure regulator and remove the six 10mm head bolts that secure the fuel rails in place (Do Not remove the two 7mm head bolts from the fuel injector locking plates) . Look at the fuel lines at the rear of the fuel rails , you will see a bracket holding the lines together . Remove the 5/16 head bolt from the bracket and remove the single 10mm head bolt that holds the bracket to the rear water tube , now you can lift the fuel rail and swing it out of the way without disconnecting the fuel lines
  15. Remove the two heater hoses from the rear water tube
  16. Remove the eight 13mm head bolts from the lower intake manifold and lift the manifold
  17. Now you will need to clean all the gasket surfaces Use a skin coat of RTV silicone on both sides of the water passage ports (outer most holes) and put the new lower intake gaskets into place
  18. Hand tighten the 13mm head intake bolts and Torque the bolts , starting from the center and working your way out in a circular pattern
  19. Torque these bolts in a few small increments until they have reached 250 inch pounds of torque

Note: Be careful when handling the fuel rail as not to put excessive force on it at any time

Note: When installing the intake air plenum , be sure to catch the four center bolts and the two side bolts (stiffener brackets) before tightening , The center bolts should be torqued to 250 inch pounds .The fuel rail bolts should be torqued to 100 inch pounds .

Feedback

Malcolm wrote:

JohnAutoTech unequivocally stated the best way to do it. That is with rtv, quick hands to stop the fluid drip, not letting the rtv set too long, use mopar fluid, and having the car up on a rack. He probably has great tools also.

With all respect to JohnAutoTech, I lack quick hands, a car rack, any skill in squeezing rtv from a tube, and have no patience for scraping gasket sealer from the pan or transmission while laying on my back. I found using RTV frustrating and switched back to gaskets. I like to change the fluid twice each time and reuse the old gasket for a few days until I can get around to the second change.

Yes, I am careful about watching for leaks and the gaskets can leak. Just wipe a paper towel around the back of the pan to check for leaks. I have changed fluid in Chrysler trannys since 1988. Changing the fluid is the key to avoiding $1200 repairs like the one I faced a few years ago. Try not to glue the gasket in place it needs to move or it might leak. Some gaskets have a few smaller bolt holes that hold the bolts in the gasket and keep everything aligned while you put it on. Don't overtighten the bolts either.

Fram filters just don't seem to click into place and hold like Mopar or Purolator filters. For the record, this is not just my imagination. I have done a side by side comparison of both and there is a difference.

Watch the rubber O-ring. It is critical to the operation of the transmission and will set an error code if missing or misaligned.

One advantage I do have is that I can let the minivan drain overnight and get more of the fluid out each time.

Conclusion: RTV gives a better seal but takes skill to do right. Gaskets can leak but any car nerd can probably get it installed decently. If you use a gasket watch for leaks not just in the beginning but as the gasket ages, hardens, and shrinks.

Finally, respect JohnAutoTech. I learn something new each time I read one of his responses. He knows what he is doing.

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