After a long damp winter, an engine wash, a deep puddle or a season on the water, moisture can collect on the spark plugs and in the wells around them. The symptoms are familiar: the engine misfires, starts poorly or not at all, and over time the contacts corrode.
This applies to cars, motorbikes, scooters and jet skis alike. You can dry the plugs and protect them from getting wet again yourself in about half an hour.
What you will need
Important: Work only with the engine switched off and cold, with the key removed. While the plugs are out, cover the holes with a clean cloth: no dirt, water or spray must get into the cylinders.
Step 1
Remove the engine cover
On most modern cars the plugs sit under a plastic engine cover. Take it off to get clear access to the coils or HT leads. On motorbikes and jet skis, remove the relevant panel or hood.
Step 2
Disconnect the coils and remove the plugs
Remove coils or plug caps one at a time and label them so the order is not mixed up. Before unscrewing, blow out or wipe the well so dirt cannot fall into the cylinder.
Unscrew the plugs with the plug socket, keeping it straight.
Step 3
Clean and dry the plug wells
Mop up water and dirt around the plug seats with a cloth. Then treat the walls of the wells with WD-40 Smart Straw through the thin straw: it drives moisture out of hard-to-reach spots. Do not spray into the open cylinder hole.
Soak up any excess with the cloth.
Step 4
Treat the spark plugs
Lay the plugs on a clean cloth and spray the outside with WD-40 Multi-Use: body, insulator and terminal. It displaces moisture and leaves a thin protective film against corrosion.
Inspect the plugs: if the insulator is cracked, the electrode badly worn or there is heavy carbon, fit new plugs instead.
Step 5
Let them dry and reassemble
Leave the plugs for a few minutes so the product can penetrate and the excess evaporate, then wipe them dry. Spray the coil connectors or lead caps with WD-40 Specialist Contact Cleaner, which cleans contacts and evaporates quickly.
Screw the plugs in by hand first, then tighten to the manufacturer's torque. Refit the coils in their original positions and the engine cover, then start the engine.
Tip: If the vehicle spends winter in an unheated garage or near water, treat the plug wells and HT leads with
WD-40 Multi-Use in autumn before the cold sets in. Moisture will not build up.
What next
Check the plugs once a season and replace them at the interval in the vehicle manual. If the engine still misfires after drying, the coil or a lead may be at fault, and it is worth seeing a diagnostics specialist.
These uses come from the experience of WD-40 users in many countries. Always follow the instructions and warnings on the product label.
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