If you have an old car that you still drive, hang onto it. I still drive a 1993 Dodge minivan. I used to haul my dogs in it. The old one died. The survivor doesn’t go for walks these days. But I’m not selling the car.
The car is my back-up. If I take my 2005 Toyota minivan into the shop, I still have a car to drive. That will let me drive the Toyota longer. The same applies to my wife’s 2006 Chrysler minivan.
It’s also good for hauling around gardening supplies. This includes rabbit manure. Bags tip over.
There are signs that indicate junk-it time.
You can’t depend on it anymore
Like our physical bodies, cars are really multiple different systems operating in concert. When it’s just one thing that’s gone wrong and once that one thing’s fixed the car can be counted on to run reliably for some time to come, doing the repairs makes sense. But when the entire car is getting obviously tired and several systems are on the verge of collapse, it’s probably time to say your goodbyes.
It’s no longer safe
Rust is the major factor here. Not cosmetic rust – structural rust. The frame (and critical mounting points on the frame). Structural damage to the frame/mounting points due to corrosion takes longer to manifest nowadays because cars built since the late ’80s are much better protected (and have better body integrity) than vehicles built before that time – when it was common to see cars only a few years old with significant rust problems. . . .
If structural rust is found, it’s time for Last Rites. The only way to fix this sort of problem is by cutting out the bad section(s) with a torch and welding in new metal – which is neither easy nor inexpensive. And then you’ve only fixed one cancerous area. If you’ve got one, odds are you’ve got more.
It’s becoming hard to find essential parts
Even if you succeed in finding the part you need, it’ll be a used part that comes with no guarantee it will work any better than the one you’ve got. Or it might only last for a few weeks/months. There’s no way to know – and no alternative.
You are putting more money into the car than the value of the car
Here’s the Catch-22 you don’t want to find yourself facing: The transmission in your 16-year-old car fails and a new/rebuilt replacement will cost you $2,000. But the car itself is only worth about that much much. If you spend the $2k on the new transmission, the car will not be worth $2k more. It will be worth about the same as it was worth before the old transmission failed.
On the other hand, if you don’t put the $2k new transmission in, the car (not-drivable and needing a major repairs) will be worth… nothing. Or almost nothing. You might get a few hundred bucks for it as a parts/scrap car. Maybe.
You can’t win.
I buy cars used. I sell them far more used . . . or give them away. This has worked for me for 35 years.