Does my car have spark plugs or glow plugs?
In short: gasoline engines use spark plugs; diesel engines use glow plugs.
Understanding which type your car uses matters for starting, maintenance, and part replacements. This article explains how to identify the plug type in your vehicle and what to look for in the engine bay.
How to determine which your car uses
Use these practical checks to determine whether your engine relies on spark plugs or glow plugs. A quick look at the engine bay and the vehicle manual usually settles the question.
- Check the owner's manual or the engine spec plate for the engine type (gasoline vs diesel). This is the most reliable source for determining which ignition system your car uses.
- Inspect the ignition components: spark plugs connect via ignition wires or coil-on-plug modules; glow plugs sit in the cylinder head with a small electrical connector and heating element.
- Look for a glow plug indicator on the dash (common in diesel engines). A lit glow plug symbol during cold starts typically means a diesel engine.
- Count the plugs in a cylinder: diesel engines typically have a glow plug per cylinder; gasoline engines use one spark plug per cylinder (though modern setups may use coil packs instead of visible wires).
- Note the ignition wiring layout: if you see thick spark plug wires or individual coil packs above each cylinder, you’re likely dealing with spark plugs; absence of such wiring and presence of glow plug wiring points toward glow plugs.
Bottom line: the engine type—gasoline or diesel—is the quickest way to tell, supported by a look at the ignition components or a check of the manual.
What you’ll see in the engine bay
These visual cues help you confirm the plug type when you open the hood. Some layouts vary by model, but the general differences are clear.
- Gasoline engines commonly feature spark plugs connected to ignition wires or individual coil packs (coil-on-plug) located atop or near each cylinder.
- Diesel engines feature glow plugs installed in the cylinder head with smaller electrical connectors and a dedicated glow plug relay/fuse cluster; you will not see spark plug wires.
- In some modern direct-injected petrol engines, you may still see coil packs, but there will be no glow plug heating elements in the head.
For most drivers, the engine’s basic type and the visible ignition components are the simplest way to identify the plug type. If you’re unsure, consult the owner's manual or a qualified technician to confirm.
What to do if you need maintenance or replacement
Follow these steps to handle maintenance or replacement correctly, especially if you’re shopping for parts or planning a DIY job. These steps assume you have identified the plug type for your engine.
- Consult the owner’s manual or a parts catalog for the correct part type and gap specification for spark plugs or glow plugs related to your engine.
- Gather the proper tools and safety equipment, including a torque wrench and the recommended anti-seize or lubrication as advised by the manufacturer.
- Follow vehicle-specific procedures for removal and installation; diesel glow plugs can require more careful handling and sometimes preheating steps during installation.
- After replacement, clear any stored fault codes, and perform a test start to ensure proper ignition and no misfires.
Note: If you’re unsure about the process or if your engine is diesel, it’s often best to have a qualified technician perform the replacement, as glow plugs can be more labor-intensive to replace on some engines.
Summary
The rule of thumb is straightforward: gasoline cars use spark plugs; diesel cars use glow plugs. Confirming which type your car has can be done by checking the manual, inspecting the ignition components under the hood, or looking for a dash glow plug indicator during cold starts. When in doubt, rely on the official specifications or a trusted mechanic to avoid misidentifying the parts or damaging the engine.
