a standard spark plug should last 10-20K KM...those better/performance type should last 30-50KM....
Spark plug is wear and tear part...
Also life span of spark plug depend on your engine condition...if your engine makan engine oil / wrong tuning then your spark plug will wear out faster.
wanna ask what happen to my fan.
My fan stops working when the weather is hot like in the afternoon stop at traffic light or when engine under high usage like going up genting highlands.