You need a new mechanic. Anyone who removes the pipes to the dashboard doesn't understand how a vehicle cooling system works. When you bypass the heater matrix, you're taking a huge chunk of circulating coolant out of the system. Less coolant flowing through the system means the engine runs hotter. More chance of overheating and causing serious damage. I would go back and kick him in the balls and tell him he doesn't understand the most basic things about how a car works.
Check that inside the radiator is clean and the fins aren't blocked and that the "mechanic" has filled the system with coolant and not just used tap water. Check that the fan comes on when the vehicle reaches temperature at idle. I would be inclined to check that the water pump is working properly too. Worth taking a look at the recirc flap and control motor too.
The bad smell could be bacteria in the system. It happens in this humid weather. You can buy cans of special disinfectant that you spray into the air intake with the ac running.
Seriously though, find another mechanic. This guy hasn't got a clue, he's a butcher.