View guide: Intake manifold gasket replacement (3.8L engine)
Written by: mrdiy

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Any engine that uses GM’s DexCool antifreeze has been known to have problems with intake manifold gaskets deteriorating and leaking. If your engine runs through a lot of coolant, but you don’t see any signs of a leak or you see water in the oil, you probably have an intake manifold leak. These instructions are for the 3.8-liter non-supercharged engine, as found in the Pontiac Grand Prix and other GM vehicles.



Disconnect the negative battery cable.

Remove the engine cover.

Remove the air intake tube.

Drain the coolant from the radiator. The draincock is located on the left bottom corner of the radiator, under the air intake.

Disconnect the top radiator hose. You will probably want to replace the thermostat at this time as well, so remove the thermostat housing.

Disconnect the rear spark plug wires from the coils and label them.

Disconnect all wires and connectors from the throttle body, fuel injectors and vacuum line connections near the intake manifold.

Remove the serpentine belt.

Remove the alternator.

Remove the throttle body.

Relieve the fuel line pressure.

Remove the fuel injectors and fuel rail.

Loosen the upper intake manifold bolts.

When all bolts are removed, you may have to pry with a screwdriver to remove the upper intake manifold. Do not pry in between the two surfaces, where you could make dents or scratches that could prevent a perfect seal later.

Loosen the lower intake manifold bolts.

There are two hoses on each side on the lower intake manifold, one is plastic and one is metal and bendable. The metal hose is attached with a bolt. The plastic one does not bolt to the manifold.

Remove the lower intake manifold; again do not pry between the two surfaces as you may cause damage causing leaks.

Clean all surfaces on the upper intake manifold, both sides of the lower intake manifold and the heads, removing all remnants of gasket and sealing materials.

Be careful that nothing falls into the ports, into the valves or other internals of the engine.

All surfaces should be dry, clean all oil, water, etc off.

At this time, it would also be beneficial to clean any oil, grease, or gunk buildup in the ports or other passages.

Place the new gaskets in place in the heads.

Place the rubber end gaskets in place and use RTV sealant (probably included in your gasket kit) to hold down the rubber end gaskets and to seal the gap between the rubber end gaskets and the lower manifold gaskets,

Place the lower manifold back into place. You will have to connect the plastic hoses on the side before setting it down completely.

Reinstall the bolts, tightening every other one.

Install the new upper intake manifold gasket to the upper manifold. There should be clips that hold it in place.

Set the upper intake in place, and reinstall the upper manifold bolts, tightening every other one. Do not over tighten these bolts.

Install the fuel injectors and fuel rail. (You may want to replace the rubber o-rings on the injectors if they are cracking or brittle.)

Install the throttle body.

Install the alternator.

Install the serpentine belt.

Connect all the wires and vacuum lines to the sensors, fuel injectors, coils or vacuum connections.

Install thermostat and connect upper radiator hose.

Install air intake tube.

Connect battery cable.

At this time, you may want to flush the radiator and cooling system, and replace the coolant with conventional fluid, instead of the original DexCool.

Fill the radiator with new coolant.

Start the engine and check for leaks.