Just how tight should wheel nuts be?

I recently bought my first car and I’m trying to learn as much as possible. Jokes that portray women as clueless when it comes to how cars operate irritate me - how tight should wheel nuts be?

Abigail

The “right torque” principle also applies to wheel nuts, and many garages are prone to chronic over-tightening. The end of that story can be stripped threads, or sheered wheel studs, and eventually a wheel coming off when driving.

Ordinary mortals can easily achieve adequate tightness with a standard wheelbrace. Spin it with a finger until it stops. Then press lightly with the heel of your hand until it will not turn any further without extra force. From that point, another hard-press quarter turn using a gripped hand (only) should be plenty. And no more force than that will be required to undo it. If it squeaks in the final tightening, that is too much. It is not a good sign, as many mechanics seem to think. That noise is a signal that damage is being done to the threads.

Punctured wheel

PS: When changing a punctured wheel on safari, make sure the wheel hub and the inside of the spare wheel are not clogged with dust or mud.

They do not have to be clean enough for the dinner table, but nothing of any thickness should be left sticking to their surfaces. Spare wheels, especially those mounted under the floorpan or on the tailgate can have months of accumulated dust or dirt-cake when time comes to use them. If substantive dirt is left, it will be squashed between the two metal surfaces when the nuts are tightened. Over consequent miles, that dirt can shake loose and fall away, leaving a space, so nuts that were tight enough to start with may now be too loose.

 Even if you have ensured both the hub and wheel rim are clean, it is a good idea some miles after a wheel change to double-check the nuts’ tightness. Again, do so with moderation.

Yes, there is a right and wrong way to change oil

Is an oil change as simple as draining old oil out and pouring new oil in, or is it more complicated than that and therefore possible to do well or badly? Other than checking the level on the dipstick after service, is there anything else car owners should monitor? Also, is engine oil still okay after it turns black?

 Peter

There are definitely right and wrong ways to change the oil in an engine. Assuming the new oil is of a good quality and a suitable grade, filled to the correct level, the most likely mistake will be how the old oil is drained out.

Oil should be drained as soon as possible after the engine has been running at normal temperature, so the oil is hot and runny and all the “dirt” in it is still churned up. Also, the filler cap must be removed before the drain plug is loosened. And the vehicle should be on a flat surface.

 All of that is necessary to ensure the oil flows out with maximum speed, carrying all the dirt with it and leaving as little as possible of the old oil clinging to the walls and components of the engine, to minimise residual sediments.

 Doing this when the car is flat is important because the sump is shaped to ensure everything drains out when it is horizontal. If the car is tilted, the drainplug hole will be above parts of the sump and ponds of old oil will be left behind.

Oil changing colour

 The black colour of old oil is mostly soot generated by combustion in the engine which accumulates over time. In new petrol engines, the quantities are minute, and even though there are millions of combustion strokes between oil changes, the oil can remain clear and golden. As the engine wears, contact with the soot in the combustion chamber and elsewhere increases, the level of soot in combustion increases, residual dirt accumulates, and the oil can become black well before an oil change is due.

Read: How often should I wash my car engine and how should I do it?

 This source of soot is microscopically fine and not hard, and therefore not significantly abrasive, so the oil can still do its lubricating job adequately (though not perfectly) until the due time for change, as long as there is not too much other detritus (shavings of metal from engine wear or dust particles from the air ingested for combustion) suspended in it.

 If the oil gets so dirty with soot and other substances (more prevalent in diesel engines) that it becomes less thin and slippery and more thick and sludgy, it should be changed without delay, irrespective of the scheduled service interval. It is the consistency and smoothness more than the colour of the oil that matters. If you take a sample of oil from the dipstick and rub it between your thumb and forefinger, and there is any sense of grit or stickiness, change it.

 If the oil is not drained properly when being changed, some “sooty” oil will be left behind to mix with the new almost immediately. That’s why the correct draining process is important.

Diligence down the drain

Another common malpractice in oil changes is the way the oil drain plug is removed and refitted. It has a sunken head (a protruding nut would risk contact with the road surface or damage from flying stones) which requires a specialised spanner (Allen Key, also known as a hex key or a larger hex wrench) of exactly the right size. Many garages do not have a comprehensive range of those, and resort to using a chisel and mallet instead. This can distort the plug so no hex key will ever fit in it again, and in extreme cases (for instance when “hammer-and-chisel” opened for the 20th time) become misshapen enough that it allows oil to leak out.

 Ideally, the plug should be refitted using a torque spanner set to the design tightness. Too loose and the seal may not be sound and allow leakage and the plug could work loose and literally fall out during ongoing use. Too tight, and the plug could distort its own threads, with similar consequences, or require even more (damaging) vigour with a hammer and chisel the next time it has to be removed for an oil change.

 The drain plug threads should be kept clean (not tossed on a gritty workshop floor) and the integrity of the washer should be checked. The quality of the new oil filter is also important, as is its pre-fit lubrication and straight attachment…to the correct tightness.

Where Hype becomes Humbug

 There’s something disturbingly weird about a drag race promoted at a motoring derby in Nyahururu. I’m searching for a logical motive for a drag race pitting a 1000hp Audi against a 1500hp Nissan, and all I can think of is subtle brand promotion for Nissan. Why would motoring enthusiasts race two vehicles with such a wide HP margin, considering the Audi doesn’t have any corresponding weight advantage to make up for the HP difference? Is this a fair race, in your expert opinion, and should it inform car preferences between the two brands? Thanks,

Joseph M

Short answer: Such a race should not inform preferences between either of the brands mentioned in any way whatsoever. At 1,000 bhp or more, I would be very surprised if showroom Audis or Nissans had anything to do with it. Hopefully, the event is not claiming to be informative…merely entertaining.

Longer answer: Is it fair? Maybe. Producing more than 1,000 bhp from an engine is one thing (and it only delivers a potential, not a result. And in this instance, I wonder how the advertised power has been measured). Delivering that power to the rear wheels is another, as is getting those wheels to put that power onto the road, as is then keeping the car on that road long enough to reach a finishing line. As you say, any difference in weight is significant to the power-weight ratio, which is a more realistic measure of likely performance than horsepower alone. Even then, the balance of acceleration and top speed will depend on many other factors, not least the gear ratios, the weight and centre of gravity of the flywheel…etc. And, at very high speeds, aerodynamics are as important as kilos.

Read: Help me decide: On my list is the BMW X1, Mazda CX-5, Honda CRV, the Nissan Skyline and Toyota Crown

Drag racing (even the cowboy-style “Street Outlaws” genre) is as different from ordinary motoring as say, a Cessna from an F15 fighter jet.

 The most powerful street-legal V8 muscle cars made by any manufacturer boast engines of about 600 bhp and the most extreme tuning and boosting (without making the original engine redundant) can raise that to about 900 bhp. That is a Le Mans level of power. Anything with 1,000 bhp or more is a very super Supercar or the next step up known as a Hypercar…the likes of Bugati Chiron and Bolide, whose prices start at $3 million and go on up to $12 million (Shs1.4 billion). Plus duty and VAT! Whose preference does that inform?

Drag racers are in another league – in acceleration, not necessarily top speed - for their standing quarter-mile events, which they readily complete in under 10 seconds. They go from a standstill to 100kph in two seconds, subjecting their occupants to 5G of force at the get-go, and they’re going so fast at the finish line (which is only a short walk away) they need a drogue parachute to help them stop. Not many roads (or even airports) around Nyahururu can offer the necessary environment for that.

 The power rating of the most extreme dragsters? 11,000 bhp! That is not so much powering off a start-line as like being fired out of the barrel of a giant cannon. In a straight line (only)…with acceleration as the overwhelming priority at the expense/neglect of any and every other attribute that might inform “motoring” choices.

 Leaving aside the more extreme engines (even by dragster standards) the more regular drag racers measure their fuel consumption in litres per kilometer (not the other way around), have a major service every day, and an engine life more likely to be measured in hours than decades.

Topically, it is interesting to see Americans at last getting passionate about Formula 1 (thanks to the enormous popularity of a new computer game, we are told) which has introduced them to lots of corners, of varying shapes, going both ways, sustained for 100 times the distance. That adds a whole new dimension to either of their two most popular motorsports: Indycar (as all the corners are left-handed, identical and helpfully banked) and drag racing (only in a straight line on the dead flat). Both are extraordinarily quick, deafeningly noisy and can be mega dramatic, but they are a bit one dimensional.

Do you have a motoring question? Email [email protected]