Motor Clinic: Car parts you never part with and parts that fall apart

Speedometer

Engine condition has no effect whatsoever on the relationship between engine revs and speedo reading. 

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Could you please highlight for me the average life spans of major parts assuming normal Kenyan driving conditions...Shocks, Tyres, Brake Pads/linings, CV Joints, Bearings, Springs, Fuel pump, Metal Fuel Filter etc. Nicholas K, Nairobi

First, segregate all car components into three main categories.

  • Service parts (often changed) like filters, plugs, points, condenser etc which are specifically designed to be regularly replaced at set intervals ranging from 5,000 to about 20,000 km. They should easily last that time unless they are physically damaged, but they should be replaced at the recommended interval even if they are still working well.
  • Fixed parts (almost never changed) which are simply part of the car’s structure or instruments and equipment - body panels, chassis members, window glasses, engine block, lights, radiator, etc which are designed to last the lifetime of the vehicle.
  • Moving parts (sometimes changed) which sustain friction and heat or other mechanical action and loads, and therefore literally “wear” out with use. These include everything from tyres and brake linings to shock absorbers, engine parts, bearings, ball joints and batteries.

The rate at which these major but ”active” parts will wear out or fail depends on a number of variables, including the make and model of the car, its load and speed, the road surfaces it predominantly uses, maintenance practices and, to a huge extent, on the style and skill of the driver.

vehicle parts

The rate at which these major but ”active” parts will wear out or fail depends on a number of variables, including the make and model of the car, its load and speed, the road surfaces it predominantly uses, maintenance practices and, to a huge extent, on the style and skill of the driver.

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To illustrate how wide the variations can be, it is perfectly possible to wear out a brand new set of tyres in 100 km, through either the most severe use and/or serious mechanical fault. However, the same tyres on the same car can last up to 90,000 km if it is mechanically sound and driven carefully A shock absorber can be smashed on a single bump, or overheated to destruction in less than an hour...or it can last for many years if is not subjected to damaging use.

“Bearings” are not a singular subject – they cover a wide range of types, uses and locations from the heart of an engine to the hub of a wheel. A con-rod bearing can be destroyed in a few minutes if it is not properly lubricated or is overheated. At the other extreme, the same bearing can last half a million kilometres or more, potentially decades!

Ditto wheel bearings and CV joints. The general principle here is that careful use, good maintenance, light loads and a gentle driving style inflict minimum wear-and-tear, enabling a good quality car to run for tens of thousands and even hundreds of thousands of kilometres with virtually no replacement.

Conversely, harsh treatment, heavy loads, negligent maintenance and poor driving technique can destroy almost any part - always sooner and sometimes almost instantly.

Exploring a myth about revs and speed

I recall reading something about the relationship between RPM, speedometer reading and engine condition. Some bigwig was saying something to the effect that a car doing 80km/h should not exceed 2000rpm if it is in good condition or something to that effect. Please clarify. Maina N

Engine condition has no effect whatsoever on the relationship between engine revs and speedo reading. The link between engine speed and vehicle speed is determined entirely by the vehicle’s gearing, and this does not change whether the engine is in tip-top condition or whether it is neglected, badly worn, badly tuned and about to cough and conk out.

The rpm-kph link in each gear is so precise and fixed it can be calculated to the smallest fraction of an rpm or kph. Many manufacturers state the kph per thousand revs in each gear in their handbooks. For instance, if a vehicle is geared to do 35 kph per 1,000 rpm on top, at 2184.5 rpm it will be doing 76.4575 kph – whatever condition the engine is in.

Speedometer

The link between engine speed and vehicle speed is determined entirely by the vehicle’s gearing, and this does not change whether the engine is in tip-top condition or whether it is neglected, badly worn, badly tuned and about to cough and conk out.

Photo credit: Shutterstock

The relationship between engine speed and the speed at which the wheels  rotate can only be changed if the gear ratios in the gearbox or final drive or wheel/tyre sizes are physically altered (ie different cogs are fitted) or if the clutch is slipping.

If during harsh acceleration, the engine revs increase much more than speed increases, this is an indication of a slipping/faulty clutch (or that the wheels are “spinning”).   But different speedo readings relative to rpm because of engine condition? No, never, no way, no how.


How to cope with on-coming dazzlers

You recently gave some most useful advice on what lights to use in heavy mist, and driving techniques to improve how well you can see in those conditions. Do you have any tips for reducing the dazzling effects of on-coming headlights, and is it okay to answer full beams with full beams?

When faced with powerful full-beam headlights, you are effectively blinded. They are the only thing you can see so the natural reflex is to look straight at them. Don’t!

Train yourself to immediately look slightly away (turning your head, not just your eyeballs) to the left where your own dip lights will still be illuminating the edge of the road for some distance in front of your bonnet. Use that, which you will still be able to see, as the focal point for your principal orientation. This action alone will reduce the intensity of the blazing light approaching you (and your peripheral vision will keep you well enough informed of their whereabouts). 

full-beam headlights

When faced with powerful full-beam headlights, you are effectively blinded. They are the only thing you can see so the natural reflex is to look straight at them. Don’t!

Photo credit: Shutterstock

Simultaneously, slowing down is also a good idea. Fighting fire with fire is not. If the oncoming full beams are dazzling you, then your full beams will dazzle the oncoming driver. That merely blinds both drivers approaching each other at speed, not solving the problem but making it even worse. Bear in mind that the person who has failed to dip in the first place is not of sound mind.

On the charitable assumption that the dazzler has simply been forgetful, while your cars are still a good distance apart it can be helpful to flash your full beams very briefly (for less than a second) as a reminder. The oncoming lights should promptly dip. If that doesn’t happen, do not flash repeatedly or turn on your beams. Stay with Plan A. Look away and down to the left-hand edge of the road.

In parallel, it is important to be aware (for your own sake and others’) that susceptibility to glare increases with age. For most people, from about the age of 45 the muscles in your iris (which regulate the dilation and stricture of the size of your pupils) take progressively longer to react/adjust to either brighter or reduced light intensity.

This reduces overall visual acuity, which means your eyes take longer to “adjust” to the dark, and are affected more intensely by glare. The older eye also takes longer to adjust its focus between, say, looking at the instrument panel just in front of you and looking at the road a long distance ahead. 

The start point and rate of deterioration in this respect varies from person to person, but the overall principle is universal. Being aware of that best equips you to make allowances for it. The common term for this syndrome is “night blindness”. If in doubt, have your eyes tested for their degree of “nyctalopia”.

Most people can still see well enough to drive safely in daylight, even at a ripe old age, but quite a number would be well advised not to drive at night.

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