I've been trying to find out what is the colder spark plug for a '87 560 SEL. Pulled out my all my plugs today. The plugs are too hot for my 6.0Litre. Does anyone know what is the next colder plug for this car? It is a Bosch W9DCO or W9DC. What is the next colder plug to this from Bosch? I am using Bosch stock wires. I want to stick with the Bosch Super, without resisitor. Don't want Bosch +4 plugs.