Reply To: high Temperature shoot up and high mach flow.

[Rob]

The warning means you're hitting the solver temperature limits so the results are going to be somewhere between misleading and rubbish when you come to plot. With pressure in and out the mass flow becomes part of the solution, and that can require carefully set initial conditions.
Use inflation and refine the mesh where you think the pressure gradients are going to be: ie do you expect jetting from the inlet pipe?
Finally, try the Pressure Based Coupled Solver. We only tend to use Density based for complex high Mach Number flows and very tightly coupled systems (combustion being one example).