Why you shouldn't panic over a missing wheel nut
The loss of one out of three nuts is a more severe reduction in security than the loss of one out of six.
Is a car safe to drive if any of the wheel nuts is missing? Several readers
One missing wheel nut does not make a car undriveable. Manufacturers do not wastefully over-design, but on safety-critical parts they will certainly leave a robust safety margin. The loss of one wheel nut will not turn a system that is very safe into something immediately dangerous.
However, if a wheel nut is lost it should be replaced as a matter of urgency – not because the wheel is in imminent danger of falling off, but to fully restore the safety margin. After all, if one nut can fall off, so can another… and with two nuts missing (especially if adjacent) the engineering equation is very different.
Also, wheel nuts don’t just fall off. Either they have not been tightened properly, or they have been tampered with (by an “interrupted” thief or vandal), or they have been mistreated by an incompetent mechanic. As soon as you notice a wheel nut is missing, you need to immediately investigate all (!) those possibilities.
Are all the other nuts on all the other wheels present and correctly tightened? A quick check would be to simply go round them all with a wheelbrace. In a fuller check, you would loosen each one and retighten it to the correct torque.
Each one should spin easily when loosened, and tighten down again to a solid stop, seated fully and straight in the wheel rim socket. Any stiffness or misalignment could indicate the nut has been cross-threaded (which could compromise its ability to stay tight when in use).
A single missing nut should not necessarily strand you. Most cars have four, five or six nuts per wheel, depending on the weight and power of the car, the size of the wheel etc. The chosen number and the size of each one will be what is required (by sophisticated engineering calculation) to “assure” that the mountings are secure and strong enough to cope with the maximum loads they will have to endure in life-long use; even if, at some point, one stud has sheared.
Clearly, the loss of one out of three nuts is a more severe reduction in security than the loss of one out of six. In the one-out-of-three case the car should be driven only briefly, gently and slowly to where the missing nut can be replaced. The strain on the remaining nuts will be considerably increased…and asymmetric, so cornering will impose a far greater strain. The strictness of those conditions can be eased, but not completely overlooked, on wheels with a higher number of nuts.
The loss of one out of four nuts also warrants prompt remedy. The asymmetry is significant. One out of 5 or 6 nuts is probably within the safety margins of design, and normal driving will be safe, even for quite extended use, once the other checks have been confirmed. Indeed, you can “borrow” one nut from each wheel to attach a tyre that has lost them all. What you have to consider is the position if another nut falls off. Safety margins are there for a reason. Tampering can loosen more than one. As ever, tighten securely but do not overtighten - that mistake is often what causes nuts to fall off in the first place, because it has distorted or stripped both the male and female threads so they no longer grip properly against the vibrations of use, or has so stressed the wheel stud that it has sheared.
For that reason, when replacing a missing wheel nut check the stud as well, and if in any doubt replace it...with an original part, not some look-alike from the PRC.
What is the secret of ‘golden oldie’ cars that just keep on going?
Compact SUV Toyota Land Cruiser (J40).
What is the secret with cars that last many decades and clock up astonishing mileages? Do most of them in fact lead very gentle lives in mild conditions, or go through several overhauls and restorations? Are they serviced more frequently and do they have lots of parts replacements? Alibhai M.
This picture answers some of your questions. When this shot was taken, the vehicle was 40 years old and had done more than half-a-million kilometers. Often heavily laden and driven quite quickly and not just in lava dust; also in mud, deep water, across fields of lava rock, and that most damaging of all surfaces – the rocky-cobbled D roads that local councils (ironically, I hope) call an “upgrade” from a dirt track. Every time this vehicle moved it was on duty as a “workhorse”. Not a pampered pet
It was (and maybe still is) a 4.2 litre straight six petrol (!) Land-Cruiser, born in the 1970s as a pick-up, later converted locally into a station wagon, and then into a canvas-topped cabriolet. Through all that, the engine, gearbox, drive train and running gear remained “unopened” and original. Fuel consumption was prodigious (5 kpl), but other than routine service parts and occasional renewals of time-limited parts (tyres, bushes, dampers, some bearings, brake pads, exhaust pipe, etc) everything else kept on keeping on.
The secret? First, the design, materials and build quality of the vehicle itself. Second, the fact its owners all used it with experience, mechanical understanding and empathy. They often asked it to go to the red line of its abilities, but very rarely more than that (which is where faster wear or damage gets done).
Third, owners observed scrupulous compliance with routine service intervals (and even more frequently, after safaris with especially severe conditions), and gave prompt attention to any fault or weakness, especially if it could have consequential impact on wear-and-tear of other parts or the whole.
That discipline actually reduces the number of replacement parts required. “Golden Oldies” don’t necessarily have more new parts. They probably have fewer, because the originals have been well made and their owners have kept them well lubricated and adjusted, and recognised the difference between hard use and abuse.
Every car has seven vital fluid levels to check
A person checks a car engine oil using a dipstick.
I get confused when checking the fluid level of my automatic gearbox. It seems to change at random, both up and down, and I don’t want to put too much or too little. How big is the danger if that mistake is made, and is there a way to avoid it?
Most cars have seven major components that need their oil or fluid to be regularly checked for the correct level and condition: the engine, the gearbox (manual or automatic), the differential(s), the brakes, the power steering, and the cooling system.
Each requires a specific quantity of oil/fluid, of the correct technical specifications, and in good condition. Each car will specify a quantity of each fluid concerned for optimum function. Each will operate adequately with slightly less or slightly more but, outside those upper and lower limits, performance will be affected and damage could be done. If the error in levels is extreme, the car will not operate properly and damage can be rapid, expensive and potentially dangerous.
The importance of regular checks is self-evident, but is not always simple. Because each component uses different materials, with different life-spans and service intervals, and different ways of measuring the levels.
Engines need this attention most often and they have dip-sticks which make the checks of level and condition (and topping up) quick and easy. They also have a wider band of tolerance between “MIN” and “MAX”. Brake fluid, power steering fluid and radiator coolant levels and conditions can also be monitored with simple “under-bonnet” checks and top-ups.
A mechanic adds brake fluid.
Manual gearboxes and differentials have much larger intervals between oil changes, but checking and adjusting levels is not under-bonnet – it is under-floor. They do not usually have dip-sticks; you have to remove the filler plug in the side of the gearbox or differential casing and stick your finger in the hole to confirm the level of oil inside and to take a fingertip sample to assess condition.
Automatic gearboxes can be the most tricky because they have less tolerance of variation in level or condition, they are also under-floor, and their fluid (conventionally ATF but nowadays increasingly more complex formulae to deal with the latest designs like CVT etc) and their fluid has more jobs to do.
Oil in engines and manual gearboxes and differentials only has to lubricate to reduce friction, and to dissipate heat from the working parts to the cooling system. Otherwise all the operational functions of the engine and gearbox are purely mechanical – movement and power is a metal-pushing-metal process.
The fluid in automatic boxes also lubricates metal-on-metal interfaces and dissipates heat, but it also has a number of “hydraulic” functions – the fluid itself does a lot of the “pushing” to transmit power from one part to another and to open and close valves that trigger both mechanical and hydraulic gear changes. Nothing I can add in a single sentence will further enlighten boffins or be meaningful to non-tech readers, so let’s just take it as a given that automatic gearboxes are extremely fussy about how much fluid there is and what state it is in.
Brake fluid can last in good condition for quite a long time but certainly not the lifetime of a vehicle
Modern warning light systems will often alert you to a problem, and if your automatic box behaves oddly (jerky or delayed changes) or makes strange noises or smells different, the level and condition of the ATF is the prime suspect.
No need to panic. Most automatics these days also have dip-sticks to make measuring levels and assessing condition an under-bonnet process, though topping up is usually still an under-floor palaver.
And here lies the probable answer to your challenge: Dip-sticks are a quick and convenient way to check oil levels deep in the guts of engines and gearboxes, but they will only give an accurate reading if the vehicle has been
* standing still
* on level ground
* with its engine turned off
* for several minutes
Only then will all the oil have collected as a single “pond” in the bottom of the engine or gearbox casing. And it is the depth of that pond which the dip-stick measures.
Some car manufacturers are fussier about coolants than others.
When the car is in use – the engine is running, the gears are engaged and the vehicle is physically moving – the oil from the pond is constantly sucked and pumped, and sprayed and squirted, and splashed and channelled through tubes, and squeezed through valves and collected and spun through torque converters and fluid flywheels, and over every other item in every other part of the engine and gearbox casings. And some of those parts are spinning at hundreds of revolutions …per second! Through that maelstrom of circulation, as fast as oil drains back into the pond (through gravity or centrifugal force) it is being sucked up and sprayed out again.
So, to measure the oil, you have to stop the circulation (switch off) and allow some time for all of it to drain back into the casing sump, which is where the dipstick takes its reading. When the oil is hot, the majority of draining will be complete in a couple of minutes.
Do not take the reading as soon as the car comes to a halt. Give the oil time to “pond”. The same “run, stop and wait” pattern should be followed after you have topped up the oil in the engine or gearbox. And on automatic gearboxes and power steerings, take note of the “hot “and cold” marks on the dipstick. ATF runs at very high temperatures and when it is hot it expands. The reading with hot oil is not the same as the reading with cold oil.
To get accurate and consistent readings, you need to observe the “pause-and-pond” protocols in the same way every time.
