I have been using Bosch platinum plugs since the first tune up at about 15,000 miles. I change them every 30,000 miles or more and they allways look like they could go more. I now have 188,000 miles. And for the listee who said they eat coils.He must have another problem, like maybe bad wires or coil wire conn. I still have the original coil on my 90 vanagon. I have not tried the quad plugs. i don't see the benifit. Happy plugging.
John 90 vanagon gl