Depending on what type of ignition the car has, removing the coil wire could be very bad. My Crane HI-6 instructions specified the use of a grounding wire between the coil tower and a chassis ground, so that the power had someplace to go, or it could fry E36 M3.
Also, I use Castrol 15w40 in my car all the time. High Zinc, and $13/gallon at Tractor Supply.