After the IEEE ballot accepted the first draft language reference manual for VHDL-AMS (IEEE PAR 1076.1) in October 1997, we now can spend time and effort on applying the new arising methodology to real world problems outside the electronic domain. In automotive engineering we have system design problems dealing with hydraulic or mechanic components and their controlling units, for which we expect a major advantage by introducing unified modelling to all domains. With the Brite/EuRam-Project TOOLSYS (a joined effort of automotive industry and tool makers to apply VHDL-AMS as unified modelling language on mixed-domain applications) we prove the suitability as unified modelling and interchange language for real-world systems and components. First experiments with hydraulic components reveal numerical problems on analog circuit simulators. None of the available strategies for these particularly hard problems are included by the electronic simulator makers. With VHDL-AMS multi-domain modelling seems possible, now we need multi-domain simulation environments.