From what i could understand from your question, you have partitioned the table based on vehicle_type and you are trying to select ALL the records from the table using select * from myschema.myoldtable;
The above query would result into a FULL TABLE SCAN and would not give you any performance benefit. The basic idea behind partitioning is to avoid access to the unwanted data by accessing only the relevant data. In your case, select * from myschema.myoldtable where vehicle_type = ‘TRUCK’ would be the correct query to benchmark the performance.
Also, note that partitioning is geneally recommended for very large tables (in hundereds of Megabytes) and it would not be a great idea to partition a table sizing few MBs.
Hope this helps.