Without a heatsink it will overheat at about 2 or 3 amps at 12v (24 to 36 watts) and shut itself down.
Could you expand on this 'automatic' feature you are talking about?
It's been my experience that it is very easy to destroy power mosfets by forcing them outside their SOA (safe operating area). Manufactures go to great detail in their datasheets to explain the limits and the need to avoid them.
Lefty