Mileage to replace ignition coils?

While ignition coils do not have a service interval, they do have a lifespan. There is no specific mileage or age to replace them. They should only be replaced when they are bad. If you notice any cracks on the plastic or epoxy, and of course misfires, then it is time to replace the ignition coils. The boots and springs can be replaced separately if they are cracking or corroded. If one ignition coil fails, and the other coils are several years old (we recommend 6 years or more) we recommend to replace all of the coils in the vehicle. Different factors can affect the life of the ignition coils such as climate, how often the vehicle is used, and age. If you live in a humid climate (anywhere in the south), your coils may not last as long as someone who lives on the west coast. 

If you live in a climate with extreme temperature changes (90° F-100° F in the summer, and below freezing in the winter) this can be hard on the plastic and epoxy as they expand and retract from summer to winter. This can lead to the body of the ignition coil cracking sooner than a coil that is not exposed to extreme temperature changes. Washing your engine bay with a water hose and pressure washer can also damage the ignition coil. We generally do not recommend anybody wash their engine bay this way without properly covering all electronics from the water. Water is a very common reason we get calls for bad ignition coils. If water gets into the connectors (and it is VERY easy to do this with a high pressure washer) it can cause a short and damage the coils, and other electronic components. 

The last reason we see ignition coils fail is from water that leaks from the wiper cowl into the engine bay during a rainy day. If you open your hood and see puddles of water anywhere, make sure to find out where the water is coming from, and clean it out asap. Using these kind of methods can help to prevent your ignition coils from an early failure.