yes I just checked my spark plugs and I used to run those Autolite 3924 so as well.. I tried one heat range hotter this year and used in NGK V Power 8..
Thank you for that tip all address that as needed.. also I'm wondering if this is more of a concern with cast iron than aluminum?..
I grabbed the two different plugs and took a picture real quick while I was out checking what I am running I forgot it's been a few months now.. and for some reason I can't find the book that I write them down in.. also I pulled the cover and looked inside my car and gave myself a shock as I forgot my seats are at the reupholstery shop...
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the next Heat range up is still pretty cold and insulator is still inside.. just not down in the hole..