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.
Thanx

gap them a little farther?
why are they buring too hot?
good luck!
adam

The difference between the W9DCO and W9DC is in the diameter of the central electrode not the heat range. The heat range is gauged by the second digit "9". I think the plug would be colder if it were an "8". In other words W8DCO.

No, the w9dco or w9dc is recommended or used for my stock model, but I have a 6.0 litre modification. The engine now runs hot. I don't know what the previous plugs were. One of my relatives brought it to someone and they exchanged the spark plugs out with w9dc. Now the plugs are overburned, all of them. I assume the extra gas or cams for combustion or whatever the modification is causing this. I checked the w8dc, but those are for the 420 SEL stock. I also checked with a cross-reference chart to see if the heat range changed any with these w8dc, but it doesn't change at all. I also assumed the same, but I don't think it is. Also, why would the 430 SEL, a less powerful engine than the 560 use a colder plug? Thanks, for the help
Any other suggestions.

Also, is the compression ration higher on a 420 SEL comapred to the stock 560 SEL? Don't think so, but I am guessing that the higher compression ratio in my car may be causing this. Any help or suggestions please.

I don't have a clue what you are talking about. The needs for plug heat range bear no relation from one engine to another. The temperature of combustion is relatively the same. What changes plug heat range is the ability for the head to absorb heat from the plug and the way the plug is mounted into the combustion chamber

Plugs have no effect on an engine overheating, actually the reverse is more likely.

Overheating engine?
I said overheated plug.

I beg your pardon. Don't mind me I often get caught in the English of the matter. The rest of the paragraph confused me equally.