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.