预热塞（Glow Plug），俗称电热塞，是一个使用在柴油引擎启动过程中的补助加热器材。

当柴油引擎启动时，因为外部的低温，使得依靠进气、压缩、爆炸、排气循环的过程，难以启动引擎的循环，此时就需要补助加温。这个设备装设在引擎气缸上部的预热室，喷油嘴下方。当柴油被喷出雾化时，会经过预热塞而被加温。当油气被压缩时，则容易爆炸，启动引擎的循环，达到正常的引擎循环工作。

按照电热塞的发热时间，可以分为慢速和快速型电热塞。

按材料分，可以分为金属电热塞和陶瓷电热塞。

A glowplug (alternatively spelled as glow plug or glow-plug) is a heating device used to aid starting diesel engines. In cold weather, high speed diesel engines can be difficult to start because the mass of the cylinder block and cylinder head absorb the heat of compression, preventing ignition (which relies on that heat). Pre-chambered engines make use of small electric heaters inside the pre-chambers—glowplugs—while the direct-injected engines have these glowplugs in the combustion chamber. The glowplug is a pencil-shaped piece of metal with a heating element at the tip. This heating element, when electrified, heats due to its electrical resistance and begins to emit light in the visible spectrum, hence the term "glow"-plug. The visual effect is very similar to that of a toaster. The fuel injector spray pattern then impinges directly upon the hot tip of the glow plug during the injection of fuel at top dead center. This enables the fuel to ignite even when the engine is insufficiently hot for normal operation. This reduces the cranking time needed to start the diesel engine.