Spark Plug Boots

Does your engine misfire in damp weather, or is the rubber boot on your ignition coil cracked? The coil boot connects the coil to the spark plug and insulates the spark. We stock boots from NGK for cars with direct ignition, where each cylinder has its own coil.

What does a coil boot do?

The boot sits between the ignition coil and the spark plug and carries the high voltage down to the plug, while the rubber insulates against the engine's metal parts and keeps moisture and dirt out. Over time, heat can make the rubber hard or cracked. The spark can then arc over to the cylinder head instead of reaching the spark plug, which typically shows up as misfires, a rough idle or an illuminated check engine light. However, these symptoms can also have other causes, such as a worn spark plug or a faulty coil. If your engine uses spark plug wires instead of coils mounted directly on the plugs, you will find them under spark plug wire sets.

How to choose the right boot

The boots are made for specific engines, so fitment determines your choice:

• Car model and year: the products list the model and years, e.g. NGK Ford Edge 2014-2007 or NGK Buick Encore 2018-2013. Always check the part number against your car.
• Length and shape: the boot must reach all the way down and sit firmly on the spark plug; the wrong type can result in poor contact.
• Quantity: if one boot is cracked, the others may be just as old, so it is a good idea to check them at the same time.

Many people replace the boots together with the spark plugs, since the coils have to come off anyway. A thin layer of dielectric grease inside the boot can make it easier to fit and remove next time. You will find other parts from NGK on the brand page, and wires and accessories are under spark plug wires and accessories.

Frequently asked questions

How can I tell if a coil boot is faulty?

Look for cracks, hard or discoloured rubber and signs of arcing – light or black lines on the boot or in the spark plug well. A misfire on one cylinder can point to the boot, but the spark plug and coil should also be checked.

Should the boot be replaced when I change spark plugs?

It is not always necessary, but it is an obvious time to do it, because the coils have to come off anyway. If the rubber is hard or cracked, a new boot can reduce the risk of misfires with the new spark plugs.

Can I keep the old coil and only replace the boot?

Typically yes, if the coil works and the boot is designed for that exact coil and engine. Check the part number and make sure the boot sits firmly on both the coil and the spark plug.