You probably already know you need to change your spark plugs, and maybe how to do it. But do you know when to replace them? If you don’t read the signs now, you could be looking at more money spent later. What does a bad spark plug look like, and what does it mean? Here’s how to figure out when spark plugs need changing.
What does a bad spark plug look like?
A “bad” spark plug doesn’t work properly, and the reason for its failure can often be determined through visual clues. What a bad spark plug looks like will depend on what caused it to fail, and they’ll all fail eventually.
Spark plugs have multiple components, and they all need to work properly. Engine vibrations can damage the insulator over time, cracking the ceramic casing. Excess heat can warp the electrode. Bad fuel, too much fuel or air and any other number of conditions can wear out the spark plug prematurely. If any part isn’t working, you will have a failing or bad spark plug.
What should a spark plug look like? If yours resembles any of the following, it’s time to change them.
Both electrodes can break, causing visible or invisible damage depending on where it happened. If either electrode is broken, the spark cannot jump the gap, meaning it won’t fire. This causes a misfire in the cylinder that you’ll definitely notice. These spark plugs should be replaced with new ones.
Soft sooty black deposits indicate an improper air and fuel mix. Check the engine air filter, ignition components or air sensors. Once that is done, clean the spark plugs with fuel injector cleaner or brake cleaner and reinstall them.
It’s unexpected to see the electrode tips wet after being inside a running engine. It’s counterintuitive but can happen. If you flood the engine by continually trying to start the engine without it firing up, all that gas soaked the plugs and prevents proper firing.
Instead of fuel, wet oil coats the spark plug electrode. That indicates worn piston rings or valve seals, allowing oil into the chamber. The solution is complicated, possibly resulting in a costly full engine teardown and rebuild.
Burned spark plugs indicate the plug got too hot. This could be caused by an overheating engine or lean running condition, ignition problems or the wrong spark plug heat range. This issue takes some diagnostic skills, but either way, you need to replace the burnt plugs.
Worn-out electrodes often indicate the spark plugs were not changed on time. This will look like the electrodes are trying to get away from each other, increasing the gap and wearing out the electrodes over time. Other signs to expect here are loss of power and misfiring.
If the engine idles rough, it’s a sign the spark plugs might be going bad. This is because the issue causes an interruption in the usual firing order, causing excess vibrations. Note this symptom typically improves some as engine revs climb.
Combustion is the reason an engine has power. When the combustion process gets interrupted, so does the power. This makes for faltering, stumbling performance or just a feeling of running on half the cylinders. That last part just might be what is actually happening.
Reduced fuel economy
That poor acceleration does more than annoy you. The decreased performance causes you to step on the accelerator harder to get up to speed. Bad spark plugs can decrease fuel economy by up to 30%.
An engine backfire happens when unburned fuel reaches the hot exhaust components and ignites, causing a loud pop or bang. While the fuel burns, it’s happening at the wrong place and time. Take this seriously because backfires are detrimental to engine performance and health.
Similar to backfires, engine misfires happen when the air and fuel mix doesn’t ignite properly, resulting in engine stumbling, poor performance, vibrations, and a check engine light. Spark plugs and other ignition components can cause misfires. Spark plugs are cheap and easy to replace, so if your engine is misfiring, the spark plugs are a good place to start diagnosing.
What to do with a bad spark plug
For cleaning or replacing spark plugs, keep it simple. If the spark plug is dirty, clean it. If the plug is damaged or broken, replace it. Also, remember to have the underlying issue checked out. If the spark plugs were simply old, a simple replacement should do it. However, misfires, oil-soaked or burn damage won’t go away by simply changing plugs.
Nelson Xavier Ssenyange
Germax Autos, Spares & Garage Ltd
Lukade Road, Naalya