Automotive Power MOSFETs to switch 80A+ - how can it work?
The legs of a TO-220 package will melt at a current of 75 Amperes or so, according to this article:


  The first surprise was that the TO-220AB package the FETs were installed in had a lower current limit than the FETs! Discussions with the International Rectifier FE and later with a rep from Motorola confirmed that the limits on the TO-220AB were approximately 75 amps. This limit was due to the heating of the lead frame to the point where the legs would melt. 


Realistically, the 120 Ampere limit might at best be achieved by applying some sophisticated cooling solution in a lab environment, not in an actual automobile product.

What is relevant though is that spikes of up to 120 Amperes might well be sustainable, if they are short enough. 

An alternative approach would be to use multiple of those MOSFETs in parallel in a combination that does not load one single MOSFET with the expected full load current.