The following has been working well for me the past 35 years; I have had my 73 Charger since 1980, My garage is not heated but in the Northeast I keep it on a battery tender, oil is changed every October regardless of miles. I will start the engine every two weeks and let it run in gear. I have the rear end raised off the floor with stands under the axel so the tires will spin, I run it about 35 mph for 20 min. This will keep the seals well worked and tranny working, better than just an idle. I wont start the car if it is been below 30deg. sometimes it sets for 3 weeks during extreme cold. I will jack the front up to rotate the tires. I do all this until about April, then will pull it out of the garage until I drive it more in late April or early May, Massachusetts has winters that last and roads are not clear of pot holes or sand until early May. To get the engine hotter I will cover the front grill radiator with a heavy towel, it cant over heat the air is too cold but it helps with a warm up. I never put anything in the gas tank, and have used Marvel oil for 35 years in the oil changes, all this has worked for me and the car always starts easy very very little oil smoke until the valve seals warm up too. Antifreeze is changed every 7-10 years with the red 7 year type, Original radiator never rust or sediment has been seen in this system. of course over the years all hoses have been changed, water pump, so that is why the antifreeze is always like new. I think it wears out with use, not just age. since I only drive the car 1200 miles a year on average it really never would need changing. Mine is always at -34 deg. when tested every fall.
