check the following
cooling fan operation-is yours an electromagnetic or the viscous type/-either way check that it is working fine.
if it is electromagnetic ,then you should hear a click when the fan engages-that is when the car is hot
if it is the viscous type-it should free wheel easily when turned by hand with the engine cold .
when at operating temperature(hot) -viscous fan,with the engine turned off,the fan should not spin more than a 1/4 turn
my 190e used to run way to hot in traffic,-it turned out to be a faulty cooling fan switch-don't know if your car has a similar switch-it may be called an auxillarly fan switch in the u.s.