My coolant comes out of exhaust pipe and truck won't start. Why is this?

What is your question?

The oil filler cap has a whitish sludge on it and the is smell of fuel coming from coolant hose fill cap- as I fill coolant, it runs out of exhaust pipe and muffler. Truck ran little rough originally when it started overheating but it overheated other day and won't start back up along with the list of problems I prior stated. What is cause? Is it head gasket or something else or is it a couple things?