What's the Difference Between Glow Plugs and Spark Plugs?
- Engine
- Maintenance
FixMyCar explains the differences between glow plugs and spark plugs.
Book a car repair nowEllie Dyer-Brown
Friday September 20 2024
2 min read
If you have questions about glow plugs and spark plugs, this guide is for you. It covers what they are, how they differ, and how often they need replacing.
What's the difference between glow plugs and spark plugs?
Glow plugs and spark plugs perform a similar job in slightly different ways, providing the ignition source in combustion engines. Spark plugs are found in petrol engines; glow plugs are found in diesel engines.
A glow plug is a heating element that raises the temperature of incoming air and fuel to make the combustion process more efficient. A spark plug, on the other hand, supplies a spark that ignites the air-fuel mixture in the combustion chamber.
What happens when a glow plug or spark plug fails?
When glow plugs and spark plugs fail, the symptoms are very similar, often causing problems with the engine, such as:
Reduced fuel efficiency
Dashboard warning light
The light pictured below signals a glow plug problem.
How much does it cost to replace a glow plugs vs. spark plugs?
The average cost to replace glow plugs vs spark plugs is similar. According to our data, the average price to replace glow plugs is £217.55, versus £150.48 for a spark plug replacement.
How often do you need to replace spark plugs?
Spark plugs are built to last; you should expect to get anywhere between 80,000-100,000 miles out of them before they begin to show signs of failure.
How often do you need to replace glow plugs?
As with spark plugs, your glow plugs should also last around 100,000 miles.
If you think you might need your glow plugs or spark plugs fixed, there are a number of mechanics in our network who can carry out the repair for you. Simply enter your registration plate and postcode on the homepage to get a quote from a specialist near you.
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