How to "Read" your Spark Plugs | Goss' Garage

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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 how mundane all

cars still use spark plugs and spark

plugs we're out now if you know how to

read the spark plugs that you take out

of your engine well 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 that the

center electrode is noticeably wore in a

way 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 looking now that

would indicate a rich mixture if it's

only on 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

all right 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 to see this is 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 you

look at that and say oh 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


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 you probably need

major 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 a comment drop me a line

right here at motorWeek