Posted on 10/30/2026
The car feels fine around town, but you're about to ask it to run for several hours with passengers and a loaded trunk. Then you remember the spark plugs haven't been changed in years. Should that go on the pre-trip list? Start with the service record. Worn plugs often become more noticeable when the engine is working harder, but mileage alone doesn't tell you whether yours are due. The engine and its plugs determine the replacement schedule. Why Spark Plugs Struggle Under Load A spark plug has to fire across its electrode gap while compressed air and fuel surround it. Climbing up the road or accelerating onto the highway asks more of the ignition than a light cruise. A worn plug that fires acceptably around town sometimes starts missing under that heavier load. The electrodes gradually wear during use. Oil deposits or other contamination can cause problems even on a plug that hasn't reached its normal interval. We'd look at the plugs and the en ... read more