Mike,

Have you pulled the valve cover and checked to make sure the valves for #3 aren't stuck open???

I would be inclined to think more of a valve issue than a head gasket. Have you checked your oil and coolant for cross contamination???

Dan

~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)