Coolant loss- any connection to a fuel injector

You could just go ahead and pre-empitvly change the head gasket now.
Then the rest is mute!

 

Preventing coolant pressure from pushing in coolant through a hg leak will eliminate start rattles for a while. It won't fix the problem and is likely to lull the driver into a false sense of satisfaction until the engine overheats.

You will only see plums of steam out of the exhaust when the coolant is going down fast and largely when the engine needs to be replaced. You need to watch at the exhaust as someone revs it up to observe it.

Cold start rattles will progress to anytime rattles when the engine restarts - such as at a traffic light.

Even at an advanced stage the severe rattling and shaking won't be every time but it will be much more frequent than the early stage once or twice a month rattle.

Losing a significant amount of coolant in a week is beyond early stage and entering risking the engine zone.