My DCo4 was doing the same thing. I replaced the filters but still overheating. Finally, I took the bin and cyclone assembly outside and washed it out with a hose. You would not believe the muck that came out. After two days to dry out, I used the hoover again and it now works perfectly.
CAUTION - only wash the cyclone. Do not get water near the motor for obvious reasons. Make sure it is all dry before use. You have been warned!!!!
John, July 2005