Mazda suggests that the spark plugs be replaced every 100,000 miles. The back three spark plugs on the Mazda 6 are located under the intake manifold. The intake manifold needs to be loosened before you remove the spark plugs.
Pop the hood and allow the engine to cool. Locate the engine cove and the intake manifold.
Loosen the three bolts that hold the dust cover in place. Use a 10mm socket to remove them. Gently turn the bolts, so they do not get damaged. Remove the dust cover from the engine.
Use the 3/8 socket to loosen the intake manifold. Loosen the vacuum hoses but do not remove the vacuum hoses. Carefully remove the manifold and set it on the side of the engine. If a gasket gets turned in the process, replace it with a new one when you put things back together. These gaskets are hard to find in auto parts stores, so you may have to find them at a Mazda dealership.
Find the back spark plug wires and remove them. Grab the tip, or boot, of the wire and turn 180 degrees to the right and left. Pull the wire of the spark plug. Replace each spark plug one at a time. If the spark plug wires are placed on the wrong spark plug, it damages the engine.
Place the 5/16 socket on the spark plug and loosen the spark plug. Pull the plug out of the well once it clears the threads.
Remove any debris or dirt from the wire boot and spark plug well. Lightly scrub them with a wire brush.
Apply a layer of anti-seize compound to the thread of the spark plug and insert the plug into the well. First tighten the plug by hand and then use the socket to tighten the plug 1/4 turn.
Replace the wire. Turn the wire 180 degrees in each direction until you hear or feel a click. Continue the process with the other wires on the back of the engine.
Replace the intake manifold gaskets if needed. Place the manifold back on the engine and bolt it in place. Return the dust cover to it's place.
Move to the front of the engine and repeat Steps 4 through 8 for the front spark plugs.
