In Summary
  • Jerky shifting or slipping are warning signs that something is drastically wrong with the transmission.
  • If your mechanic sees that the car has had all four corners repaired, that might be an indication that the car has been driven by a reckless driver who is probably reckless about maintenance, too.
  • Though the odd full-throttle puff is considered normal as particulate is blown out of the exhaust or the fuel injection system ups the air/fuel mixture for a moment, continual smoking, especially at idle, is never a good sign.

When buying a used car, you will have to contend with the fact that there are many copies of any given model to choose from and most are in decent shape. However, they also have two things working against them, too. First, you probably do not know who owned it before and how they took care of it. Secondly, since that used car is a machine made of parts and components and assemblies, its mechanical condition is largely subject to how the previous owners handled it.
Regular readers will be familiar with common used-car checks to make, the importance of a mechanical pre-inspection and how to tell if the car in question is in good condition or not. This time we shall play the walk away game. This is where you will look at and consider some factors and then look for another car if some of them are not satisfactory.

Shifting issues
Jerky shifting or slipping are warning signs that something is drastically wrong with the transmission. Warning signs of trouble on a manual transmission include a gearbox that bites back at you when you shift gears, or grinding when shifting, even slowly. Further, a manual gearbox that pops out of gear likely needs some attention, too. Gear boxes are not cheap to fix with most mechanics recommending a replacement and walking away from one that is about to self-destruct can save your wallet.
Obvious signs of a spoilt gear box include dings, dents, strong odours and ugly stains. By themselves, superficial signs of neglect are not a big deal, but a person who does not care what his car looks like or smells like may not care about its mechanical condition, either.

Accident damage
Everyone has mishaps, so it is not a deal-breaker if the car you are considering has been in an accident. Almost every car “of a certain age” has at the very least a scratch. However, if your mechanic sees that the car has had all four corners repaired, that might be an indication that the car has been driven by a reckless driver who is probably reckless about maintenance, too.
Or, if the car has been in a particularly serious accident, you can have unexpected problems later on, such as electrical gremlins from pinched wires or uneven tire wear due to a bent frame and inability to align the wheels. Typically car bodies are laser aligned so any form of misalignment on the body panels is indication of work done.
Once you finish your personal inspection, write down everything you have noticed that seems questionable to you. Having a friend with you to document all this can help as well. These are all the things you will want to mention to your mechanic when you bring it in for an inspection.

Smoke
Though the odd full-throttle puff is considered normal as particulate is blown out of the exhaust or the fuel injection system ups the air/fuel mixture for a moment, continual smoking, especially at idle, is never a good sign.
If there is smoke, chances are the engine has bad valve seals or piston rings. Neither are cheap to change. White, oily smoke at idle on a turbocharged car means the turbo is probably too old and very heavy, sweet-smelling smoke from the tailpipe means the coolant is burning up in the combustion chambers, meaning you could have a blown gasket on your hands. Repairing most of these is very costly and you are better off avoiding them in the first place.