First of all thanks for the reply ;)
First try putting a 1K resistor in the base circuit between pin11 and the transistor base, it needs the resistor to limit the base current and not over load the arduino.
I tried the 1k resistor in the base of the transistor and i observed that the motor rotated verry slow or didn't rotate at all . Then i changed the 1k resistor with a 300 ohm resistor and all worked fine (but didn't solve the heating problem).
When the motor is running, what is the voltage on the collector with respect to GND and your power supply and GNDd?
Windscreen wiper motors are quite a load, you may need to measure the running current.
I measured the voltage at power supply and gnd and i had 12 V , I didn't get to measure the voltage on collector and gnd because i think i just burned the transitor :). I will try to put a new one and do this measurement. I measured the current consumption and at low speed is around 2,5-3 A and at high speed is around 6 A.
In my opinion it would be better to use a logic level control MOSFET, as it does not require the base current that a transistor does and has a much lower switch on drain to source resistance.
I tried to use a mosfet (irf630) but i get the same result, tha transistor get's really hot. :(