Blender has a global cache limit.
You can change that limit in the user preferences (Ctrl+Alt+U on windows) in the system tab.
You’ll see a Memory Cache Limit at the bottom of the middle column. Default value is 1024 (1Gb) but you can change it to any value you like. Multiples of 1024 are usually prefered to keep things clean. I don’t know if smoke sim uses this cache limit but you should give it a try.
8 high res may be a little high for smoke simulation. Maybe if you bring it down to 2 or 4 it’ll save heaps of memory without noticeable change.
Thank you for the answer, I knew about this setting but it’s listed under “Sequencer/Clip Editor” so I thought it has nothing to do whit simulations…
Has someone ever made a simulation with cache files bigger than 1 GB?