Spark plugs used to be so cheap it made little sense not to change them regularly. In those days spark plug electrodes would visibly erode and demand more spark voltage and even filing them flat and regapping would not restore as-new performance.
These days most spark plug types are somewhat specialised - made from better materials, providing an extended life with little reduced performance. This is reflected in the price paid and the cost of some types is eye-wateringly painful.
One vehicle I looked after had covered 70,000 miles on the same set of plugs without the tell-tale rounding of the electrodes even under a strong magnifier. I had checked them every 10,000 miles only to put them back (with some copper grease on the threads and a smear of silicone grease on the insulator). I eventually replaced them as a matter of form but I think they would have done in excess of 100,000 miles without trouble.
I suggest you remove the plugs and look at them in good light through a magnifier and replace them only if electrode erosion is taking place and the gaps have widened significantly, if there is heavy ash/carbon deposits (almost unheard of these days) or the dreaded town running deposits are apparent. This yellow/green tint to the insulator colour is electrically conductive and usually formed when a person drives steadily in city limits all week and then at the weekend leaves the city limits and accelerates rapidly to high speed instead of building the speed slowly. Town running creates a buildup of ash and carbon that will burn off when speed is built slowly whereas sudden acceleration can bake those deposits so they become an integral part of the insulator.
Answers & Comments
Spark plugs used to be so cheap it made little sense not to change them regularly. In those days spark plug electrodes would visibly erode and demand more spark voltage and even filing them flat and regapping would not restore as-new performance.
These days most spark plug types are somewhat specialised - made from better materials, providing an extended life with little reduced performance. This is reflected in the price paid and the cost of some types is eye-wateringly painful.
One vehicle I looked after had covered 70,000 miles on the same set of plugs without the tell-tale rounding of the electrodes even under a strong magnifier. I had checked them every 10,000 miles only to put them back (with some copper grease on the threads and a smear of silicone grease on the insulator). I eventually replaced them as a matter of form but I think they would have done in excess of 100,000 miles without trouble.
I suggest you remove the plugs and look at them in good light through a magnifier and replace them only if electrode erosion is taking place and the gaps have widened significantly, if there is heavy ash/carbon deposits (almost unheard of these days) or the dreaded town running deposits are apparent.
This yellow/green tint to the insulator colour is electrically conductive and usually formed when a person drives steadily in city limits all week and then at the weekend leaves the city limits and accelerates rapidly to high speed instead of building the speed slowly.
Town running creates a buildup of ash and carbon that will burn off when speed is built slowly whereas sudden acceleration can bake those deposits so they become an integral part of the insulator.