Steam... a few people brought that up when I came back... you said from "contaminated oil" do you mean condensation in the block over the years ends up in the oil? I would think it would not mix, end evaporate out the valve cover breather? Or leaking headgasket causing coolant to be burned in the chamber and the steam goes out the exhaust? But usually when I have had that problem (even very minor) the combustion pressure makes its way into the cooling system and out the relief on the radiator cap... Or condensation in the exhaust? Maybe it took till 4th gear to get the majority of the exhaust hot enough to burn enough to make that much steam - sounds kind of strange - but sometimes anything is possible...
