Use something like the LM2940 as its been designed for use on automotive power. Also read the datasheet carefully and choose the output capacitor accordingly as it has to be within certain tolerances to stop the LM2940 oscillating.
I agree, you need to use a voltage regulator IC that is specifically designed for the automotive environment. The hazards that such ICs help with include:
- reverse polarity connection
- overvoltage during jump starting (to at least 24V)
- load dump. This is an overvoltage spike in the + or - direction that can be as high as 200V and occurs when high current loads are switched off (like headlights) and the parasitic inductance of the vehicle wiring causes a back EMF spike. It is short duration but may be relatively high energy.
- impulse noise due to alternator and other rotating or intermittent electrical loads
- high level RF from VHF two-way radios. This is usually only a problem if you have a radio in your vehicle.