Question of the week: When do I need to change my spark plugs?
Fri, 13 Mar 2026
Dear Honest John,
"I have a Ford Fiesta Active X that I've owned since 2021. It has 36,000 miles on the clock. Starts first time every time and is a great car.
I'm having a full service now. Does it need plugs renewed even if it starts perfectly? What's your advice?"
- AC
Dear AC,
When it comes to maintenance, it's tempting to skip over scheduled items because the car is working well. But the reality is that consumable parts such as spark plugs, air filters and engine oils will slowly degrade every time the car is used, and you are unlikely to notice until these parts are really worn.
Spark plugs play a key part in engine performance, as a good spark means an efficient and powerful detonation of the fuel and air mixture in the cylinder. It is possible that you could leave the original spark plugs in place and it would run well, but changing them for new ones would help to keep the engine in the best possible condition.
While the recommend service interval for spark plugs on EcoBoost engines can be as high as 100,000 miles depending on the use case, we would suggest that while your mileage is relatively low the spark plugs are now approaching five years old and a new set would be a sensible investment.
