Ask a Technician: What Happens to Car Engines as They Age?

The easy answer to what happens to car engines as they age is that they wear out. The much more complicated answer is exactly what begins to wear in an engine and when it does. The standard everyday vehicle engine is a reciprocating engine. This means that a series of pistons push down on a crankshaft, which changes the pushing and pulling motions of the pistons into a rotating motion that is passed on to the gearbox and then to the car’s wheels.

A lot of engine components either reciprocate or rotate at very high speeds and high temperatures, but modern-day engines are well built to handle this as parts that will wear out are usually easy to replace. The first thing likely to happen is the camshaft drive belt failing, and this can certainly damage your engine if the pistons smash into the valves, resulting in a big repair bill. All carmakers have a preset mileage at which the camshaft drive belt should be replaced, and some cars even have maintenance-free chain drives that do not have to be replaced.

Spark plugs are another thing that need to be replaced at a set interval, as the plugs themselves can burn out or become too dirty to work properly. These usually just screw in and out of the engine and are an easy fix.

The main wear inside the engine comes from all the moving parts. When correctly maintained, the oil in a car’s engine fills the tiny spaces between the moving parts so the parts themselves are not actually touching. Some wear does occur, especially in the early days, when the engine is “breaking in.” This is merely the process where all the different parts wear ever so slightly so that they all work smoothly together. That is why most automakers suggest that you not treat the engine too harshly or run it to extreme speeds for the first 1,000 miles or so.

In the long run, the cylinder bores will wear out the piston rings. These rings keep the oil in the engine from getting into the top of the cylinders where the fuel is being burned. That’s one of the main reasons why old or poorly maintained cars have a dark smoky exhaust – it is oil that has gone through the cylinder heads and out the exhaust.

The engine’s bearings can also wear out. These are metal inserts in the rods that connect the pistons to the crankshaft. If they begin to wear out, it’s easier and cheaper to replace the bearings and not the entire rod.

These last two types of engine wear should occur over a very long time period, unless there is some sort of manufacturing defect or a lack of maintenance, such as not changing the oil and oil filter at the prescribed intervals. Oil collects all the tiny bits of metal that can wear away in an engine and the filter removes those bits from the oil flow. So not only does oil keep your engine running smoothly, it also keeps it clean and free of stuff that can increase the wear rates.

Engines do wear out, but unlike in the old days, modern ones can last for a significant length of time if proper maintenance is carried out.