slant 6 problem

When I suspect antifreeze in the exhaust, I swab my finger around the inside of the tailpipe and taste my finger, looking for the telltale sweetness.
Make sure you are not confusing the gray smoke for water vapor which is a normal by-product of combustion. The smoking is always more pronounced with a cold engine, with a cold exhaust system, at cold ambient, and on high-humidity days.