sql query runs long time and always seem to fill out temp

The developer is trying to execute a query for report purpose. The query seems to run four a long time and always seem to fill out the temp tablespace. I did added another 1Gb to the temp tablespace, but still filled up. Gurus, please advise whether this query needs tuning or is having syntax issue maybe. Thank you very much.

Below is the query:

select productinfo.serial_no,
testdata.tst_rvalue, testdata.tst_judge, testdata.upd_date from t_prd_info
productinfo, t_tst_data testdata

where testdata.upd_date >=
to_date('03/20/2014', 'mm/dd/yyyy')

and testdata.tst_id = '123456'