I'm surprised it has been in there that long and not started leaking.
I've got them in my other cars,but not my GN. Installed them myself. Just knock out a freeze plug and install. Messy job. Got my winter car plugged in right now since I have to go to work at 1:30am and it's near 0'F.
Just running out and plugging it in on a cold night,won't do much. It really helps if you plug it in when the engine is already hot. On a 0'F night with no wind,my 3300 (sort of like a 3.8) will be about 80'F after 10hrs or so.
I have trouble with the Kats brand of these heaters,which I believe that is a picture of. That looks exactly like mine. The Kats brand sort of half burns-out and don't get as hot after a while.
There usually isn't a long cord from these heaters. You need to use and extension cord to plug it in. The shorter the better.