When to Replace Spark Plugs
Spark plugs are often the first suspect when a gasoline engine misfires especially when it has not been serviced for quite some time. Diesel engines do not have spark plugs. This is often caused by fouled, dirty, carbon covered or worn out tips. Sometimes cleaning, filing and re-gapping the tips would put them back in good condition.
When to replace the spark plugs is the question. Here are some points when a spark plug or the whole set of them needs to be replaced:
1. The tips, center electrode worn down too short or side electrodes are worn too thin. Cleaning and filing would only make them worse because the gap can not be properly set.
2. Broken or chipped external ceramic insulator and also the insulator around the center electrode.
3. When fouling is caused by either a “cold” or “hot” spark plugs. Your mechanic should be able to tell you if your driving routine will need either type. Cold plugs dissipate heat faster than hot plugs.
4. Check the continuity of the center electrode with the other end (terminal) where the high-tension wire socket is connected. If there is no continuity, or shows to be erratic, there must be a break within. (This is a personal experience that really surprised me!)
5. The washer is worn out that might cause the spark plug come loose. Tapered spark plugs do not have washers.
Please take note that replacing the spark plugs will just be a temporary fix if you have not determined the cause of spark plug failure. The following could be reasons why spark plugs fail:
1. Over-advanced timing that will ruin the electrode tips.
2. Pre-ignition when the engine still runs a little more after it has been switched off. There might be some particles in cylinder or piston that remains aglow causing it.
3. Some oil getting into the cylinder resulting to varnish coated spark plug tips that can eventually lead to fouled up plugs.
4. Incorrect gap setting. Too narrow gap will cause to burn the tips prematurely. Large gaps can cause some undetectable misfiring that can foul up the spark plugs.
5. Bad high tension wires that can also cause some undetectable misfiring. You can check for continuity, or run the engine in the dark. If you sparks jump from the cable in the dark, it can be cleaned if not replaced too.
6. Water can also seep into cylinders if water-jacket in the engine block has gone bad. This can cause mineral deposits on the tips of the spark plugs.
Precaution: If you want to test for spark while engine running or being cranked, 30,000 volts surge through the high-tension wires. It can give an unpleasant jolt or shock when held with bare hands in the process.
