My coil failed this last summer after a 150 mile drive. The center contact in the cap was fried as well. The next day the coil in my buddy's 69 fried on the freeway coming home after only a couple minutes on the road. His cap looked fine but it was following a week of 100deg weather. These were both in-cap coils. I think with the heat generated under the cap these coils have a finite life span. I've gone to carrying an extra coil in the trunk just in case until I can change over to a dist with a separated coil.