The glow plugs inside of a John Deere tractor are the main components that aid in the internal engine combustion process. The glow plugs heat up the compression area inside of the piston cylinder so that the diesel can ignite. Diesel takes longer to ignite than gas. Hence the use of glow plugs to assist in the temperature increase so that the diesel can ignite and the pistons can compress. If the glow plugs stop working, they will not be able to heat the compression area and it will cause the engine to take longer to crank.
Pull the bonnet back on the John Deere and secure it in place so that it does not fall.
Remove the air-cleaner housing from the top side of the engine. Remove the bolts and nuts from the housing with a ratchet and a socket. Pull the air-cleaner housing off the engine and place it on the tractor's seat. The glow plugs can now be accessed.
Locate the glow plugs that are inserted into the top driver side of the engine. The glow plugs are inserted into the engine in the same manner that spark plugs are. Each glow plug also has a wire attached to the top of the plug by a single nut.
Turn the ignition key on the John Deere to the accessory position. Turn the multimeter on and move the settings knob to the voltage section. Touch the positive prong of the multimeter to the wire that is attached to one of the glow plugs. Attach the negative prong of the multimeter to the side of the engine. The voltage reading should be between 12 and 13. Turn the ignition key off.
Inspect the wire that is attached to the glow plug to ensure that it is tight. Also ensure that the glow plug itself is tight inside of the engine. Move to the other glow plugs and repeat the same process as outlined above.
Remove the nut from the top of the glow plug that secures the wire to the plug with a ratchet and a socket. Turn the nut counterclockwise to remove it from the glow plug.
Insert a glow plug socket onto a ratchet. Lower the socket over the top of the glow plug until the socket is over the hex head of the glow plug. Turn the glow plug counterclockwise with the ratchet and socket until the plug is loose. Remove the ratchet and socket from the glow plug.
Remove the glow plug by unscrewing it with your fingers. Move to the other glow plugs and repeat the same process as explained above to remove the glow plugs from the engine.
Apply a thin layer of anti-seize thread seal onto the threads of the new glow plugs. Screw the new plugs into the engine by hand and tighten each plug with the ratchet and socket until the plugs are tight. Once the plugs are tight and have stopped turning, finish tightening the plugs by turning each plug another one-quarter of a turn with the ratchet and socket.
Reattach the glow plug wires to the top of each glow plug. Screw the nuts onto the top of each glow plug and tighten the nuts down with the ratchet and socket until the nuts stop turning. Reinstall the air cleaner over the top of the glow plugs. Test the new glow plugs by turning the ignition key on for five seconds. If the John Deere has a glow plug buzzer, the buzzer should stop buzzing after five seconds.
A deep-well socket can also take the place of a glow plug socket to replace the glow plugs. The anti-seize thread seal will prevent the glow plugs from freezing up inside of the engine. This makes it easier to remove the glow plugs again if necessary.
Do not over-tighten the glow plugs or the glow plug wire nuts. This can result in stripping the glow plug threads and the glow plug wire stud threads.