Sounds like you need a new mechanic

Anyways, it's very easy to test the radiator flow:
1. When engine is cold, drain all the coolant from the radiator
2. remove the bottom hose from the radiator
3. Cover the bottom outlet with your palm, and fill the radiator with plain water from a hose
4. When radiator is full, quickly remove your palm
- If the water gushes out the same amount as the bottom outlet, that's a good sign
- If the water trickles out, or runs out but in a stream smaller than the size of the outlet, the radiator is partially plugged

This happened to me. The radiator didn't look plugged, but it was. This can cause the suction hose to collapse as well, since the pump is on one side and a restriction on the other.