Here is a spark plug comparison. On the left, please note the severely worn electrodes as compared to a new ones on the right.

Standard plugs are replaced as part of the Major service at 30,000 mile / 2 year intervals. Some platinum or iridium-tipped spark plugs will last about 60,000 miles. Pay no attention to the folks that tell you to wait to replace them until 100,000 miles. The threads will have become one with the cylinder head creating a very costly repair.

Motor Works is always working for your long-term benefit.

Your spark plugs shouldn't look like this...This is how your spark plugs look when they're new...