Filtration and Engine Wear

Increase a vehicle’s service life with routine engine oil and filter changes

In spite of technological advances in lubricants, materials and manufacturing, engine wear has not been eliminated. Sure, engines last longer than ever before, but that doesn’t mean that the parts inside the internal combustion engine are not wearing. Wear cannot be eliminated. Any time there is movement between two surfaces that are in contact, wear will occur.

The major cause of wear in an automotive engine is dirt. More specifically, this dirt is the silicone-
based abrasive material that is everywhere around us. Air and oil filters prevent the engine from 
becoming contaminated with this dirt, but these filters have a specific service life. And if that service life is exceeded, dirt contamination and the resulting engine wear is a real possibility. Also, operating a vehicle in a dirty environment can lead to dirt contamination.

THE AIR FILTER

All automotive engines have an air filter. Figure 1 shows a typical air filter element. Fifty years ago, the air cleaner assembly was mounted on top of the carburetor. An air horn provided the intake passage for air. On modern vehicles, air flow into an engine is much more directed. The point of intake is usually near the bottom of the engine compartment with tubing leading up to the air cleaner housing. The incoming air passes through the air filter element through a passageway into the throttle body.

The incoming air is dirty, thus the need to filter it. As a result, the filter element becomes dirty and, over time, requires replacement. As a general rule, you can’t go wrong with replacing the filter element once a year. Remember, too, that the inside of the air cleaner housing should also be cleaned. Dirt will accumulate inside the housing, so it’s important that it be cleaned.

When installing a new filter element, be sure that it is properly seated in the housing. If it’s not, the housing cover might not seat properly on the housing. Also, be sure that all the clasps that secure the cover are fastened correctly. A cover that is improperly installed can allow unfiltered air to enter the engine.

THE OIL FILTER

In order to keep the lubricating oil in an automotive engine clean, it must be filtered. Any dirt or other foreign material that is in the engine is picked up by the oil as it circulates throughout the engine. This includes metallic wear particles, carbon and any dirt that might get through the air filter.

Figure 2 illustrates a typical oil lubrication system in the engine block. The oil is drawn up from the pan by the pick-up tube, then travels to the oil filter before circulating to the lower gallery that feeds the main and connecting rod bearings. At points 1 and 2, the oil travels to the cylinder heads to lubricate the camshaft, cam followers and valves. The oil drains down by gravity through the heads and the block back to the oil pan and the cycle repeats.

As is the case with the air filter element, the oil filter has a specific service life. Changing the oil and the oil filter in an automotive engine is the most basic of maintenance tasks that can be done to ensure long engine life. The usual service interval is about 3,000 to 7,500 miles, depending on the service conditions.

DIRTY AIR AND OIL

If an air filter element becomes dirty and clogged, abrasive material will get into the engine. While some of this dirt can be carried away by the circulating engine oil, much of it is not. Tight clearances in the valvetrain (valve stem-to-valve guide) and engine block (piston skirt-to-cylinder wall) prevent this dirt from being swept away. Often these abrasives are lodged in the clearance spaces. This is where the problems begin.

The dirt that is picked up by the circulating oil can be removed by the oil filter. But what happens when the oil filter hasn’t been changed for 20,000 miles? Two things. First, any dirt in the oil cannot be effectively removed by the filter and, secondly, the dirt is now carried throughout the engine, making the contamination problem worse.

Dirt can also enter the engine at the time the oil is changed or added. While most oil containers are designed as self-pouring, be sure the outside of the container is clean. In automotive shops and quick-change service facilities, oil is usually pumped from a barrel and fed into the engine through a nozzle. The outside of this nozzle can easily become dirty. Be sure the nozzle is cleaned every time that it is used.

ENGINE WEAR

When there is movement of one or both of two contacting surfaces, wear occurs. If there was no lubricating oil in the system, this movement would generate a significant amount of friction and heat, leading to the rapid deterioration of the surfaces. In an automotive engine, oil provides a thin film of lubrication that prevents metal-to-metal contact and minimizes wear. There are contacting surfaces throughout an engine that must be protected from excessive wear (piston/cylinder wall, bearing/journal, valve/valve guide, etc.). As long as the oil remains clean, friction and wear are minimized.

When dirt particles contaminate the engine, either through the oil or the air intake system, engine 
wear can be quick and destructive. But how does this wear actually occur? The mechanism is actually pretty simple.

Dirt particles become entrapped in the clearance spaces between any two moving parts. When this particle is large enough, it breaks down the oil film between the two parts. This high spot acts like a little grinding wheel, wearing away at the moving parts. Now, imagine thousands of these dirt particles causing wear on bearing journals, cylinder walls and valve guides. The clearance between the two parts becomes excessive, breaking down that thin film, resulting in metal-to-metal contact.

When the clearance between the valve stem-to-valve guide becomes excessive, oil enters the combustion chamber and builds up on the valve face. This oil can foul spark plugs, causing driveability problems.

As the bearing-to-journal clearances increase, oil pressure drops. Excessive clearance can lead to connecting rod knock which, left unchecked, can cause failure of the small end of the rod. If that happens, extensive engine damage is the result.

Dirt can also become embedded in the face of the piston rings. This causes cylinder wall wear and increased blow-by. As this wear increases, the piston rings can no longer seal the combustion chamber properly and sweep oil off the cylinder walls. This leads to oil build-up in the combustion chamber, more oil burning and spark plug fouling.

Abrasive engine wear is a progressive problem. It gets worse as time goes on. The metal particles that are worn off the cylinder walls and valve guides end up in the engine oil and are circulated throughout the engine. These particles also cause wear. Over time, the engine is destroyed, requiring a complete rebuild.

SUMMARY

As you can see, the air and oil filters play an important role in maintaining the serviceability of the modern automotive engine. If these filters are cleaned and/or changed as recommended, and installed properly, engine wear will be minimized. On the other hand, if dirt gets into the engine as a result of a dirty air filter, or a dirty oil filter can’t remove it, the engine can be destroyed as a result of abrasive wear. Once the cycle starts, it feeds upon itself and can’t be stopped.