C drive losing space fast each time I try to use Unreal Engine although EVERYTHING is on a different drive!

[ClockworkOcean]

Bear in mind that 253MB is nothing. I think maybe your C drive is full of something else?..

Even if you move your vault and projects, the engine still sits on C:

You can move the engine using:

[Windows] Moving installed Unreal Engine 4 into another system

or this looks a bit better:

wiki.unrealengine.com