If you keep a car for a very long time, the moment will come when you are going to inevitably put it in the back yard and leave it there for good. You are going to know when it's time to say good bye to your car, because the servicing costs will be higher than its total value. Many people would see this as an inevitable loss. In fact, you could trade your junk car for cash and put this amount against buying a new car. This is how to turn your junk car into cash:
If your car is already a bunch of junk, you need to discover some junk yards that accept cars for scrap metals. Ask all of them for a quote and see if you like any of them. You may be surprised to see how much money you can get on a piece of junk you thought didn't have any value at all. If you don't know where to find junk yards, you can either look online or in classifieds pages of local newspapers. You are going to have your car inspected by technicians from the junk yards, then they are going to make you an offer. If you have a well-known make and model, you could sell various parts of your car and make more cash than if you'd sell it as a whole.
If your junk car is a classic, all you need to find is a collector of such cars. Collectors buy classic cars and invest a lot in repairing them, not because they actually need a vehicle to move from point A to point B, but because they want this specific make and model to be part of their collection.