Spark Plug question

[Joe Craven]

I'm running stock heat range plugs in my 1971 2000cc Capri. I'm concerned that they may be running a bit hot, especially since I found some little round metallic balls on the number 4 insulator.

Anybody know how the manufacturers numbers work. For example, the motor takes a Motorcraft 42 or Autolite 45 plug. Can I specify a different number to get a colder plug that still fits?

[joeg]

Yes, Joe.

Typically, the lower the number, the colder the range--Autolites for sure go that way.

Try one number down on the Autolite and see if they make it.

I'm sure you can Google this too.

Cheers.

[C. Ludwig]

Except for NGKs which have a higher number for a colder plug.