What Parts To Replace When Servicing A Car & Why.

Regularly servicing your car is still the best way to save on maintenance costs in the long run, but do you know why certain things are replaced at certain times during a car’s life? Why not change everything in one fell swoop and be done with it until next time? Well, you could do that if you are not concerned about costs, but that is not the only reason.

The main reason has to do with the fact that some parts have finite service lives, and in this article we will look at why it is imperative that some parts and fluids be replaced on a regular basis during routine servicing to keep any car in peak condition. Let us start with the engine oil..

Why replace the engine oil?

While oil replacement intervals differ from car to car, the general rule is that oil should be replaced at around every 6 000 miles, instead of every 3 000 miles as was the case only a few years ago.

However, all new cars should ideally receive an oil and filter change during the first 1 000 or so to remove all the wear particles that result from breaking in an engine, but after the first oil change, the manufacturers recommendations must be followed religiously, and here is why..

While the additives in modern engine oil do a great job at reducing mechanical wear and keeping engines clean, they can do so only for a limited time before they start to degrade, and break down. The main reasons why this happens is that some additives react very strongly with oxygen, and the friction modifying additives are the first to suffer from oxidation. Oxidized oil forms harmful sludge, and the only way to prevent this happening is by replacing the oil at the prescribed intervals.

Other reasons include contact with combustion products and moisture, which creates sulphuric acid, a highly corrosive agent that can wreak havoc in any engine if it is allowed to reach critical concentrations.

In older cars, the degradation of oil is accelerated by defective or clogged PCV valves, whose function is the effective ventilation of the engine to remove volatile substances, and even though the replacement of this valve is a prescribed service item on almost all cars, it is sadly often ignored or overlooked, so be on the lookout for a defective PCV valve if you detect sludge in your engine.

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Why replace the oil filter?

This should be self-explanatory, but if the oil filter clogs up and no longer allows the passage of oil, the dirty oil is allowed to by-pass the filter through a by-pass valve in the filter housing. In short, this means that dirty, unfiltered oil is pumped around the engine. To prevent this from happening, the oil filter MUST be replaced at every oil change.

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Why replace the air filter?

Air filters are designed to filter out dust, grit, and other solid particulate matter from the air before it enters the engine, where it can cause serious damage by scoring the cylinder walls and piston rings, thus destroying the rings’ ability to contain the combustion pressure on the one hand, and to control the excess oil on the cylinder walls on the other.

Scored cylinder walls cause increased oil consumption, damage to catalytic converters due to high levels of hydrocarbons in the exhaust gas, and reduced spark plug life due to unburned oil being deposited on the electrodes. There is more though- a clogged air filter also starves the engine of inlet air, which causes increased fuel consumption, and all of the other problems associated with scored cylinder walls.

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Why replace the fuel filter(s)?

You will be amazed at the amount of dirt and crud that gets pumped into your tank together with the fuel you buy at the pump. High pressure fuel filters are excellent at removing this crud, which consists of sand, water, corrosion, and other unspeakables, but they eventually get clogged up. When this happens, the engine is starved of fuel but besides that, the fuel pump can suffer fatal damage by having to force fuel through a filter that is now an effective plug in the system.

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Why replace the spark plugs?

Spark plugs supply the spark that ignites the air/fuel mixture in gasoline engines, and although modern high performance plugs can last for as long as 60 000 miles and more, they eventually fail because of the cumulative effects of high temperatures, high pressure, and the fact that the electrodes literally burn away through a process known as “spark erosion”.

This increases the air gap across which the current must jump to create a spark, and this places huge additional loads on the entire ignition system when the gap gets too big. This is one of the main reasons why ignition coils fail, so keep an eye on how the engine idles, or performs under sudden acceleration, even though the spark plugs were replaced recently.

While ignition coils are not service items, the symptoms of damaged ignition coils include misfires, hesitation, increased fuel consumption, hard starting, rough running, erratic idling, and even frequent stalling that are often misdiagnosed, so keep an eye on the condition of the ignition coil(s) on your engine by having a full diagnostic check performed at least twice a year.

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Why replace the timing-belt?

The timing belt regulates the opening and closing of the engine valves, and it, and its associated tensioning device(s) are most definitely service items. Most manufacturers recommend that the timing belt (and tensioner) be replaced every 60 000 miles, but there are exceptions. Some belts need to be replaced every 90 000 miles but whatever the prescribed replacement interval, it must NEVER be exceeded.

Some engines, called “interference type” engines can suffer very serious, and even irreparable damage when the timing belt fails because the pistons slam into the valves with immense force, since the valves are no longer regulated. On non-interference engines, the engine will just shut off when the belt fails, but the associated towing and repair costs can run into many hundreds of dollars.

In some cases, the timing belt is routed by several idler pulleys, and although they are not strictly service items, they must be checked very carefully at each timing belt replacement. The smaller the pulley, the faster it rotates, and the bearings that support them can’t last forever, so look out for signs of free play, or noisiness in all pulleys that are in any way associated with the timing belt.

The failure of an idler pulley will always cause the timing belt to fail, so play it safe, and have all pulleys replaced as a matter of course when you have the timing belt replaced.

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