request a BLOCK HEATER from the dealer.
do not know if NAPA would have one.
it replaces one of the FREEZE PLUGS that is now in the motor.
i have seen the lower radiator hoses that heat up but have no idea if
they are worth it. my guess would be no.
this must be plugged in to the house current to work.
don't expect your foot to get toasty once it starts up but with my old
300sd it takes much less time for the heater to put some warm air out.
the newer motors like yours warm up faster <i have been told> than the
Tiger if he sees this may be able to tell you whats involved to install
you may have one in there already
all 3 of my older<2> 300sd & <1> 240d <82 84> had them. look on the pass
side under the hood up front for a plug.
the case, minus a few cans!