Glow plugs are pencil-shaped objects that help diesel engines start. In essence, they serve as the diesel equivalent to spark plugs found in gasoline engines. Unlike spark plugs, glow plugs use heat to get the engine going. In cold weather, glow plugs play an especially important role. This is because diesel engines often experience ignition troubles when temperatures are low. Diesel engines require the air to reach a certain temperature for fuel ignition to occur, but they tend to absorb heat when they are cold. Glow plugs help solve this problem by providing enough heat for the fuel to ignite. However, glow plugs usually require a small amount of time to warm up before they can perform. While they gather heat, glow plugs let off a small light or glow. As a result, this process is often referred to as “glowing.” After the glow plugs finish warming, drivers should be able to successfully start their diesel vehicles.