Living in the age of "fake news" and misinformation is such fun, isn't it? But baseless myths are nothing new: we just used to call them other things, such as "old wives' tales". I was never quite sure how that saying came about. Are old wives more likely to give flawed advice than members of other demographics? Where's the evidence?
But we digress. Myths, misapprehensions, whatever you want to call them, can actually cause us to waste a fair bit of time and money. In some cases, they can even get us into trouble with the law. We've checked out half a dozen bits of car maintenance advice that we have heard offered at one time or another, to determine whether they are wisdom worth acting on, or just nonsense.
Myth 1: Tyre pressures can get dangerously high in hot weather, so you should let some air out of hot tyres to bring the pressure down to normal
This is incorrect. Tyres are manufactured to tolerate a range of pressures. The benchmark pressure that we should use to assess our tyre pressure is known as the cold pressure or cold inflation pressure. That should be our starting point. Tyre pressures should be measured before driving, when the tyres are cold. That is also the time to do any top-up inflation if pressures have dropped.
Letting air out of hot tyres creates a risk of driving on underinflated tyres if conditions change and the tyres cool down. This can happen unexpectedly, when one drives through water, for example. Incorrect tyre pressures shorten tyre lifetimes and increase the risk of accidents.
Instead of deflating tyres in extremely hot weather, it is better to avoid leaving cars parked in direct sunlight, and to take a break from driving to give your tyres some time to cool a little, if you suspect that they may be getting too hot.
Myth 2: It's a good idea to slightly overinflate tyres so they go longer before needing to be pumped up again
More nonsense. Different cars require different tyre inflation pressures to ensure safe and economical running. Overinflated tyres can cause reduced traction, raising the risk of skidding. Overinflation can also reduce the lifespan of your tyres.
Both overinflation and underinflation can both damage tyres and increase the likelihood of accidents.
Myth 3: After requiring a jump-start, a car should be fine after a drive around the block. If that's not enough to get it back to normal, then the battery is worn out and needs replacing
If a battery has drained so far that it doesn't have enough charge to start the car, then you should try to identify the likely cause. If you left some electrical system running - leaving a light on, for example - then the problem should be easy to spot. However, if there is no obvious cause, then the issue could be with the battery or with a component such as the car's alternator. If you don't know why your battery went flat, get the car checked over by a mechanic.
If, for example, you left the lights on overnight and needed a jump-start from your neighbour, then you should drive the car for at least 20 minutes to give the battery a chance to recharge to some extent. A longer drive is preferable. Alternatively, use a car battery charger to give your battery a proper recharge.
Myth 4: Modern cars don't need "running in" like cars from the last century. It's fine to drive a new car fast from the outset
Modern cars don't need running in to the same extent as older cars, but many manufacturers do still recommend limiting revs and speed for an initial break-in period.
BMW's website says:
[...] You should avoid running the engine at high RPM for the first 1,300 miles. Experts recommend a maximum 3,500 rpm and 90 mph in diesel models and 4,500 rpm and 100 mph in gas models. This will give the engine and transmission sufficient time to adjust to each other."
In practical terms, that shouldn't make a huge difference to UK drivers as the speeds mentioned are all way over our maximum speed limit anyway, but the fact remains that cars do still require a degree of breaking in before overenthusiastic new owners thrash the life out of them.
Myth 5: In very cold weather, the car should be left to idle for 10 minutes before driving to warm up the engine
No, extended periods of idling are unnecessary. Modern car systems make it fine to start the engine, give the oil a few seconds to circulate in the engine and then drive away. Leaving a car idling for long periods just increases wear and tear on the engine, wastes fuel and emits pollutants and carbon unnecessarily.
That doesn't mean that one should drive the car hard before the engine has warmed up. Metal components such as valves, pistons and shafts gradually heat up and expand. It is best to give the car's parts a chance to reach a kind of equilibrium by warming up uniformly before making harsh demands on the engine. Similarly, BMW recommends not switching off a hot engine suddenly but, instead, drive the last few miles at "a gentle pace" before switching off.
Myth 6: After topping up the oil, mechanics add a little more "for luck" to make sure the oil level doesn't drop between services.
This is incorrect. Engines are designed to work within specific oil pressure ranges. Overfilling with oil can cause the oil pressure to exceed that range, resulting in oil leaks, compromised performance and possible damage to the engine. Your dipstick will have markings showing maximum and minimum levels. Always top up the oil within the indicated range.
The safest way to ensure that your DIY maintenance efforts really are helping your car rather than harming it are to consult either your owner's manual or a qualified mechanic. Your car's manual will contain all the information you should need. It may not be the most absorbing of books for most people, but finding out a few basic bits of practical information about looking after your car can, at least, be mildly interesting. It can also save you time and money.
