When should you replace your engine’s glow plugs?

Although heavy-duty diesel engines moved to direction injection many years ago customers still operate machines with older pre-combustion engines and can experience glow plug problems.

Glow plugs are an essential part of your engine, so it’s important to keep them in good working order. Here at Jaytrac, we’re on hand to help you diagnose your engine problems, and have compiled this handy guide to help you recognise the signs that your glow plugs need replacing.

What is a glow plug?

Glow plugs are a heating element of an engine; they use battery power to generate heat and are used for the ignition process. Like most parts of your heavy-duty engine, glow plugs can suffer from normal amounts of wear and tear, and it’s important to keep an eye out for the indicating signs that they may be damaged or faulty.

Hard starting

The clearest indicator of needing a replacement glow plug is if your engine refuses to fire, or won’t start. If your glow plugs are damaged or faulty, you may find your engine is particularly hard to start from cold, or in cold weather conditions. In this case, your engine may be firing but not immediately on all cylinders. If your engine requires excessive cranking when cold, or it won’t start at all, be sure to inspect your glow plugs for damage and look to replace them if necessary.

Misfire on startup

Whilst hard starting is one of the biggest signs of a faulty glow plug, you may also find engine misfire on startup to be another indicator. For example, you may have started your engine, but find it to not be firing properly, and this is often indicated by unusual noise or knocking sound.


A potential indicator of faulty glow plugs may be smoking or excess smoking upon your heavy-duty engine’s startup. If you notice unusual amounts of smoke from your heavy-duty engine, switch it off and inspect accordingly.

Abnormal Starting

When your engine is in good working order, take note of the usual starting characteristics, such as noise levels, amount of smoke and time taken to start. If any of these factors change and starting becomes an issue, it’s important to investigate and a good starting point is to check glow-plugs.

It’s crucial to recognise the signs of faulty parts within your engine. If you notice any of the symptoms above or any other signs that parts of your engine are damaged or faulty, make sure to act quickly and use quality replacement parts to avoid any further damage! If you need help diagnosing issues with your engine or if you are on the lookout for replacement engine parts, get in touch today and we’ll be happy to help. As specialists in quality replacement heavy-duty engine parts at Jaytrac, we are the genuine alternative to suit your needs.