Diesel engines are unique in the automotive world, in that they do not use an ignition system to ignite their fuel mixture. A gasoline engine utilises a timed spark, delivered at the precise moment, at the spark plug gap. A diesel engine,instead relies upon heat to get the job done. The high compression ratio of the diesel heats the combustion chamber mixture to a point where it ignites. In cold conditions this can be difficult, requiring a lot of cranking of the engine to build up the needed heat. Glow plugs preheat the combustion chamber air, allowing quick starts.
Raise the hood of your vehicle and locate the glow plugs. On some Ford vehicles the glow plugs are located under the valve covers. Remove any components which block access to the glow plugs, such as valve covers or wiring looms.
Spray the glow plug with penetrating oil at the spot where it threads into the engine. Allow the penetrating oil to soak into the threads for at least 20 minutes.
Place the appropriately-sized socket over the glow plug. Be certain that it fits the plug properly. A loose socket can slip off and break the glow plug, as it is hollow. Hold one hand on top of the ratchet and push in toward the engine as you turn the ratchet handle counterclockwise. This keeps the socket from popping off of the glow plug. Continue to turn the glow plug counterclockwise until it is completely unthreaded.
Coat the threads of the new glow plug with anti-seize compound and thread it into place on the engine. Hold the socket tightly, with pressure toward the engine, while you turn the ratchet handle clockwise until tight.
Glow plugs have a definite lifespan, so it's a good idea to buy them before they fail, so they will be on hand when needed.
Do not use high powered "jump start" battery chargers on glow plug-equipped vehicles.The added voltage can burn up glow plugs. Do not wire glow plugs to run continuously. This will cause them to burn out quickly.