2004 Ford F-150 - Glow Plug

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What is a Diesel Glow Plug?


The glow plug is an electric heating device used in diesel engines to aid in cold-engine starting by acting as an igniter and heating fuel and air during the starting process. Diesel engines don't rely on spark plugs for combustion, and instead are fired by engine heat and high compression. When a diesel engine has sat and cooled down, especially in the coldest months of the year, the air in the diesel engine's cylinders may not be hot enough to combust, and the engine may fail to start. The glow plugs on a diesel engine heat each individual engine cylinder to aid in cold-weather starting and are commonly found beside each fuel injector. Glow plugs are essential components to starting diesel engines when they are especially cold, and extremely low temperatures can make starting your diesel more challenging if the glow plugs are not working as they should. If your diesel engine experiences hard idling, excessive white smoke, or fails to start in the cold, it could be an indication of a failing glow plug. Diesel glow plugs are designed for a long service life, although hard starts or low-quality glow plugs can cause these components to wear and fail prematurely. While you may be able to start and run your diesel with bad glow plugs, it's recommended that you check bad glow plugs and replace them if needed ahead of the cold season to ensure smooth, reliable starting and prevent long start times that could cause engine damage. For assistance finding the correct parts for diesel engine repairs, shop O'Reilly Auto Parts for a complete line of diesel replacement parts, including glow plugs, fuel injectors, and more.