3. Engine issues
Internal combustion engines have hundreds of pieces, so there's lots that can break, but some failures are more likely than others. Skaien specifically points to engine hoses: "By the time your car is 10 years old or it's got 100,000–120,000 miles on it, you should seriously be looking at replacing your hoses," he says, "even if they look fine." Another common culprit: oil and fluid leaks. "Manufacturers are getting better and better about sealing engines up well so they don't leak. But you should attend to leaks quickly. If you see any fluid on the ground, no matter what color it is, try to find the matching color underneath your hood and get it into a shop right away."
Having low oil is a related problem, though one that's harder to notice. If you're not checking your oil regularly, your first indicator that you're low is likely to be a "low oil" dashboard warning. "If you see a picture of an oil can that's red come on your dash, shut the engine off right away," Skaien says. Check the oil level and, if it's low, add enough to reach the minimum before driving. "If it's full and that light's on, you probably should not drive it."
If the engine's timing belt snaps while driving, the engine will suddenly shut down. If it snaps when the engine is off, the issue will instead present as an engine that cranks irregularly and won't start—similar to a failing battery, but with the cranking sound randomly speeding up and slowing down as the engine tries to start.
Hoses that suddenly break while driving will lead to rapid engine overheating.
Oil or fluid leak
An oil or fluid leak may leave fluid on the ground, but the lack of residue doesn't mean there are no leaks. Fluid leaks can humidify the engine compartment and lead dirt to accumulate on wet engine surfaces near the origin of the leak.
Use a disptick to make sure your oil isn't dipping below the minimum level. Don't wait for the "low oil" light to come on—at that point, your vehicle may not be safe to drive and the engine may suffer internal damage. Check your oil level at least once a month, or more frequently if you drive a lot.
A snapped timing belt will cause a sudden engine shutdown if it breaks while driving, or as an engine that cranks irregularly and won't start if it breaks while the engine is off.