I understand that its possible to cache Google maps for offline use.
But is it possible to search or calculate new routes with the pre-cached map without connecting to internet?
This is not possible at the moment (but maybe in the near future).
Maps is deliberatly an online service, Google wants you to be "connected".
You have to either buy one of the many pro routing apps (from Navigon, CoPilot or others) or use one of the Open Street Map apps that also provide offline routing (I really like OsmAnd+ or OsmAnd free). See also Open Street Maps wiki for more apps and info.