Blue Smoke=Burning Oil. Black Smoke=Raw Fuel. White Smoke=Water in the combustion process. Sounds Like the old blown head gasket. Due a cylinder compression check on the 4 on that side, you will probably find 1 or 2 leaking water. Also if you idle the engine and pull off the pressure tank(closest to engine),cap, You should be able to smell/see exhaust coming out off the water. You'll also have to add water/coolant to bring the level higher, since you have been loosing it all along. Marlin.