Glow plugPanama

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139. Glow plug

A glow plug is an electrical heating element used in diesel engines to help ignite the fuel during cold starting. It heats the combustion chamber so that the compressed air reaches conditions suitable for reliable combustion.

Modern glow plugs can continue operating briefly after the engine starts to improve combustion, reduce cold-start emissions and help the engine run smoothly while warming up.

Glow plug
Diesel preheating and glow-plug dashboard indicator symbol.
Wikimedia.org • Chris828 • CC0
What does a glow plug do?

A glow plug heats the combustion chamber of a diesel engine before and during cold starting so that the injected diesel fuel can ignite more reliably.

Do diesel engines use glow plugs instead of spark plugs?

Diesel engines normally ignite fuel through compression rather than an electrical spark. Glow plugs therefore assist cold combustion but do not continuously ignite the fuel in the same way that spark plugs do in a petrol engine.

What are signs of faulty glow plugs?

Possible signs include difficult cold starting, rough running shortly after startup, increased cold-start smoke or a glow plug or engine warning light. Similar symptoms can have other causes, so proper diagnosis may be necessary.

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