Streetka Overheating

I bought my 2004 Streetka almost two years ago. It worked fine for a long time, until a few months ago I noticed it seemed to start overheating. Even a brief 2 kilometer drive would heat up the engine so much, the ventilator can be heard running at maximum speed when you turn off the car. The air coming from the heating system is also so hot, it literally burns your hands. I am genuinely scared my engine is going to explode one day. This problem started all of a sudden, so it's not 'just the way the car is built'. Another problem, but possibly unrelated, is that fuel consumption of the car seems abnormally high all of a sudden. Like, I can only drive 300 miles on a single tank.

I checked the coolant liquid, it's fine. The two garages I've been to for this problem detected no issues whatsoever. They say the ventilator kicks in at the correct temperatures, but that doesn't mean the engine isn't overheating... Would it be possible the water cooler is broken (and somehow the oafs at those garages didn't see it)? If not, could one install a second coolant tube to increase the flow of coolant? I really need this car for work, I am close to broke, and this problem needs to go away.