The cache in magento , over time , uses up more and more data until the server is crashed.
How do I automatically have magento clear the cache so my server does not crash AGAIN :
In /admin > cache management > auto cache these 3 :
Additional Cache Management
Flush Catalog Images Cache Pregenerated product images files.
Flush Swatch Images Cache Pregenerated configurable swatches image files.
Are you using something different to the base file cache of Magento?
Can you check if the var/cache directory is the cause of the problem? (checking the size of that directory over time)