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Spark Plugs: Professional Glow Plugs | ACDelco

ACDelco Professional premium aftermarket Glow Plugs are specially designed to give diesel engines the heat they need for cold starts. They will maintain ignition in all cylinders, improving throttle response and reducing exhaust emissions. These premium aftermarket replacement glow plugs fit a variety of diesel engines and are manufactured to meet or exceed your expectations for fit, form and function.


Find out more about ACDelco Professional Glow Plugs and how they fit into the Ignition System with the product facts below.

Features & Benefits:

  • Designed to give diesel engines the heat they need for cold starts
  • The ACDelco Professional Glow Plug can function under higher voltages than other glow plugs
  • GN-type regulating coil
  • Self-regulating to control electrical flow from battery as temperatures rise to avoid overheating
  • Full range of reaches – from 21 mm to 40 mm – to meet chamber requirements in a wide variety of applications


  • Function:

    A high-voltage spark from the ignition coil ignites the air/fuel mixture inside the engine’s cylinders.

  • Signs of Wear & Troubleshooting:

    Signs that you might have problems with your glow plug and need to replace it are:

      • Damage to the heating rod, which can be caused by overheating, atomization beginning too early, choked, worn or dripping nozzles, seized piston rings or a closed annular gap between plug housing and heating rod.
      • Deformed plug or missing bolt, which can happen when excessive torque or an incorrect tool is used to tighten the plug.

  • Did You Know:

    Most vehicle breakdowns are due to one of five causes:

      • Out of gas
      • Stalled/engine won’t start
      • Dead battery
      • Flat tire
      • Overheated engine

    Most of these breakdowns can be avoided through the following measures:

    1. Periodic mechanical checkups, especially when engine stalling, hard starting or other such symptoms are signaling trouble
    2. Regular tire inspection to spot damage, unusual wear or under inflation that can lead to the failure
    3. Seasonal checks and preventive maintenance of the cooling system, a frequent factor in roadside breakdowns
    4. Be sure the gas cap is on tight after filling up to safeguard against condensation in the tank. If moisture in the gas line freezes, the engine can stall.

    Also, having a cellular phone or portable CB radio is of great benefit while traveling.

What It Does:

The Starting and Charging System starts the engine, maintains the battery’s charge and provides power to the electrical accessories while the engine is running.

Good Maintenance Practices:

It is important to inspect spark plugs at regular intervals for signs of deterioration. Follow these steps for removing spark plugs for inspection, servicing or replacement:

  • Grasp the spark plug boot and gently rotate it 90 degrees counterclockwise. Pull the spark plug boot and cable away from the spark plug. If necessary, use spark plug boot removing tool. DO NOT grab or violently pull spark plug cables.
  • Use the correct deep socket size to loosen each spark plug one or two turns. NOTE: To remove spark plugs from aluminum heads, allow the engine to cool. The heat of the engine, in combination with a spark plug that is still hot, may cause the spark plug threads to strip the cylinder head upon removal.
  • Brush or air-blast dirt away from the well areas before removing spark plugs. CAUTION: Use goggles to protect eyes from dirt when applying compressed air to spark plug wells.
  • Remove each spark plug and place each one in a tray by cylinder number. This will help identify and relate any unusual condition to the cylinder involved.
  • Apply dielectric grease into the boot area to reduce the chance of exterior tracking on the buttress tower of the spark plug. This grease also promotes a good heat transfer between the spark terminal screw and boot terminal.
  • Before installing new spark plugs, use a gap guide to make sure your new spark plugs have the correct gap. NOTE: ACDelco Professional Iridium Spark Plugs are pre-gapped during manufacturing. Never attempt to gap an ACDelco Professional Iridium Spark Plug. You could damage the spark plug. Replace the incorrectly gapped ACDelco Professional Iridium Spark Plug with one that is correctly gapped.



Should I change my spark plugs every 3,000 miles?

  • No, it depends on what type of spark plug your vehicle requires. Refer to your Owner’s Manual or contact your vehicle’s manufacturer for more information.

Can changing my spark plugs improve my engine’s performance?

  • Yes, but spark plugs may not be the only factor impacting performance. Replacing old spark plugs may temporarily improve poor engine performance due to reduced demand on the ignition system. However, this is not the cure for poor engine performance caused by worn rings, faulty carburetion, worn distributor parts or other engine performance issues.

Should I change all of my vehicle’s spark plugs at the same time?

  • Yes, if it is the scheduled time for spark plug replacement. It may be OK to replace one spark plug if it was broken for any reason prior to scheduled maintenance.

Does a diesel engine require a different type of plug than a gas engine?

  • Yes. Diesel engines require glow plugs because diesel engine ignitions operate differently than gas engines. ACDelco Professional Glow Plugs are specially designed to give diesel engines the heat they need for their cold starts.

Are ACDelco spark plugs pre-gapped?

  • Yes. When ACDelco spark plugs are manufactured, they are pre-gapped to the correct gap specification.

When I replace my spark plugs, should I also replace my spark plug wires?

  • Not always. Refer to your vehicle Owner’s Manual or contact the manufacturer for more information.

How do spark plugs become fouled?

  • Certain engine conditions can cause oil, powder and carbon to collect on the spark plug, causing a misfire. See our list of Signs and Causes of Spark Plug Wear.

What is pre-ignition and can it damage my engine?

  • Yes, pre-ignition can cause serious damage to your engine. Pre-ignition happens when the spark plug is too hot and fires before the piston is in the correct position.

Can I just clean my spark plugs instead of replacing them?

  • No, cleaning your old spark plugs is not recommended. Dirty, fouled spark plugs may also have broken, chipped insulator tips, worn electrodes or worn or missing side wires. These conditions severely affect spark plug performance. Replace your dirty, fouled spark plugs with new ACDelco spark plugs.

Does ACDelco have marine spark plugs?

  • Yes, ACDelco has marine spark plugs for many applications.

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