Are you trying to do internal analysis with a non-airtight model? Use the leak tracing tools to find out where the cracks in the model are.
You might want to do a parasolid export and them import and run import diagnostics. See what kind of model you actually have. Since you haven't bothered to provide sufficient information for any one to really help you it hard to know what to suggest.
Guess: probably an aerodynamic test for the flow around that car --> external analysis.