Spark Plug Diagnosis

You know back in the day, cars had a lot of ignition parts that today don’t even exist.

Like spark plug wires. But no matter how exotic or mundane, all cars still use spark plugs. And spark plugs wear out, now if you no how to read the spark plugs that you take out of your engine, you can determine the general condition of your engine.

Now look at this spark plug: we’re looking right at the center, and we see the center electrode is noticeably worn away. Well that’s normal wear; nothing wrong with the engine there, that’s just too many miles on a set of spark plugs.

Now the next one, the end of the spark plug is black, dry…and dry is the key, black dry and sooty looking. That would indicate a rich mixture. If it’s only one cylinder, you probably have a leaky fuel injector. If it’s on more than one cylinder, then you probably have an overall fuel control problem.

Now this next one: really, really clean, spotlessly clean, cleaner than any of the other plugs in the engine. That usually signifies that coolant is getting into that cylinder and it is cleaning, steam cleaning the end of the spark plug.

Alright next: this is what we hope to see. We have a little bit of discoloration, the electrodes are worn evenly and everything is clean…there are no deposits. That is normal.

Now here’s one we don’t want see. Here’s one where the end of the spark plug has dry sandy, now in texture, not in color…dry, sandy looking deposits that have built up primarily on the outer electrode. Look at that, say uh oh, got some bad valve seals….means  oil is being sucked into the engine in an atomized state, and it’s usually coming around the valve seals or the valve guides.

The last one: this is really a bad one. The end of the plug is all gunked up and filled up with deposits and so on…it’s wet, it’s oily, it’s greasy looking…that means that liquid oil is coming from the bottom of the engine either around or through the piston and your probably need major repair internal engine repairs.

So learn to read the spark plugs and you’ll know a lot more about the general condition of your engine…and if you have a question or  comment drop me a line right here.

by Pat Goss

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