Can't say if you have a BHG or not... looks like smoke coming out ?
But, you don't have a legitimate overflow tank/coolant reservoir/expansion tank or
whatever you want to call it. So you top up your radiator when it is cold, go for a
drive to get the engine up to temperature, and the coolant expands. It has nowhere
to go so it lifts the valve inside the radiator cap and spills out over the radiator. You
can see the "rust" coloured traces all around the water neck. Then you take a look
after your drive, see the coolant level is down a bit and top it up. Repeat...
What is supposed to happen is that the expanding coolant pushes out the overflow
hose that you have blocked off. That hose goes to the expansion tank and the end
of it is below the level of coolant in the tank. When the engine cools down and the
coolant "shrinks", ir causes a vacuum that draws coolant back up the hose into the
radiator so the radiator tops itself back up
You can make a temporary overflow tank with a length of hose, an empty plastic
bottle and a few zip ties. Half fill the bottle with coolant and fix the hose so that
the end always stays at the bottom of the bottle and is fully covered by coolant. If
you continue to lose coolant after every drive, then maybe you do have a leak .
Cheers... jondee86