Do cars need oil changes more or less often as they age?

Car engines wear out as mileage increases. Older and higher mileage engines have lower tolerances, requiring more frequent oil changes.

Although the engines used in today's cars may seem exceptionally modern, if you take a close look at their basic principles, you will find that they are still related to engines developed in the past. For example, Ford introduced its famous V8 engine in 1932. As any experienced auto mechanic will tell you, the basic engine architecture has remained the same since its introduction. It is important to note that regular oil changes are still necessary, but the type and age of the engine matters when this occurs.

Engines tuned to suit

It is true that major changes have been made to the engines as new tunings and other engineering tweaks have been applied to improve their performance as well as to ensure they meet EPA standards. However, the basic architecture - gallery layout, piston angles, etc. - has remained the same over the years.

One way to change engines is to significantly tighten internal tolerances. In the early days, overhead cylinder heads were very soft due to the metallurgy of the time. This dictated the use of low compression ratios in the engine. In turn, the low compression ratio meant that performance was relatively consistent as the long-legged engines could run at 65 mph for hours. However, it took a little time to get there. It wasn't until the invention of tetraethyl lead for use as a gasoline additive that the automotive industry was able to increase the compression ratio to make engines run better. The tetraethyl lead provided lubrication to the top of the cylinder and meant the engines could run more reliably.

Engine tolerances weaken over time

Although they share many similarities with their predecessors, modern engines are designed to much tighter tolerances. The tolerances are such that engines run more efficiently at higher compression ratios. This means that fuel consumption can increase and emissions can be reduced.

However, engine wear inevitably develops and tight tolerances begin to loosen. As they weaken, oil consumption tends to increase. This is somewhat inversely proportional. As engines wear, oil consumption increases. As oil consumption increases, oil change intervals tend to shorten. Where oil used to be changed every six months or 7,500 miles, it now needs to be changed every three months and 3,000 miles. Over time, the intervals are likely to get even shorter.

Specific engine requirements affect oil changes

While gasoline engines tend to run at one end of the scale, diesel engines tend to run at the other. From the beginning, diesel engines had tighter tolerances. Tighter tolerances are due to the need to work at high pressure and high temperature. Pressure and temperature were dictated by the fact that diesel engines are autonomous. They use self-ignition as engines rely on the pressure and temperature generated by compression to ignite the diesel fuel. Diesel fuel also burns more efficiently.

Because the diesel is self-contained, any emissions or other contaminants that are produced get into the oil and cause oil wear over time. Oil change intervals on diesels can be up to 10,000 miles, however, as the oil wears or internal parts wear, more frequent oil changes may become necessary.

Cars may need more frequent oil changes over time

The need for more frequent oil changes is usually associated with engine wear. As engines wear, once tight component tolerances become larger. In turn, this requires more oil usage, and as more oil is used over time, more frequent oil changes are required. Mobil High Mileage is specially formulated for older engines and reduces leaks by burning off power-damaging deposits.

The specific type of engine may determine the need for more frequent oil changes. For example, a diesel engine operating under high pressure and temperature is a closed system that creates its own unique conditions. Special emissions and other engine by-products are produced that can contaminate the oil and cause it to wear out earlier. Also, engine temperature causes oil wear. These factors may require more frequent oil changes.