4WD's and Beating the Dust.shtml

It's called Pindan in the north of Western Australia, and 'bulldust' nearly everywhere else and it's an insidious nuisance that can be problematic to control within the confines of a 4WD.

It gets into the back of instrument gauges, behind perfectly sealed headlights, on the upper side of folded up sun visors and into every last thing that you least want it to enter. And there is not a thing you can do to completely eliminate it other than travel solely by aeroplane. There are however many things you can do to minimize its ingression.

roadtrain along a dusty road
Prevention

It may seem patently obvious to mention - but the best way to avoid dust inhalation in a 4WD is to avoid driving in it. Travelling in convoy on heavily dusted roads is a sure method of eating plenty of the stuff. This can be substantially reduced by maintaining a following distance that allows the dust of the preceding vehicle to settle. This distance can be anything up to 15km. There is not much to be done about traffic coming from the opposite direction but there are things that can be done to minimize contamination from oncoming traffic (let's face it, contamination is what it is). More on this later.

When entering the vehicle make a habit of getting everyone to bang the sides of their feet and 'drop' as much dust as they can. Keep it out of the car from the get-go. This is probably the most useful feature of aftermarket running boards.

Dust Theory & Positive Air Pressure

Dust enters our cars because it is suspended in the air and we are passing through it. It also enters if we create a low pressure zone inside the cabin. The higher pressure outside the 4WD tries to equalize with the interior pressure and the cabin 'sucks' the dust in. The faster we travel the more air is forced through or sucked in and consequently, even more dust has the opportunity to enter. If we can reduce the amount of air that passes through the 4WD and create a high pressure zone inside the cabin, then we can minimize the amount of dust that is carried through the vehicle.

Positive air pressure, (while we are moving) is, theoretically, the complete removal of all air leaks from behind the front vents - where air is designed to enter the car. If no additional air enters the car then no additional dust is brought inside. This of course is impossible. If it was possible to completely block all airflow then we would have a vacuum, the car would be crushed by the air pressure differential and we would all have expired from suffocation by now. Cars are designed to allow a fresh supply of air to enter the cabin from the front.

Positive air pressure, inside your 4WD, is created when you allow the outside air to enter your vehicle and create a 'buffer' on the inside. Allowing this air to enter the car means switching the fresh/recirculate control to fresh. Similar to a highly inflated balloon, air enters the car through the front vents and can't escape through the rear, creating a high pressure zone inside the car. This creates a wall like effect that 'punches' through the dusty atmosphere holding the dust at bay.

Good rear sealing means the air enters quicker than it can escape under the pressure of forward motion. Turning the fan on to high means even more air is forced inside further pressurizing the cabin. Driving with the air conditioner on creates denser air inside the cabin - providing an even 'stiffer' wall to hold out the dust.

It is realistically impossible to 100% seal all the leaks in a vehicle (as impossible as it is to barricade 100% of the dust) and some air will always pass through the car - allowing some dust to enter. Approaching vehicles stirs up an enormous amount of airborne dust. We find that temporarily switching the controls from fresh to recirculate when driving through clouds of stirred up dust, minimizes the impact.

People who drive brand new 4WDs report that they find having the controls set to 'recirculate' may provide better sealing than having it set to 'fresh' and experience suggests that the sealing capabilities of a car fresh from the showroom floor may be so good that dust simply cannot intrude. Experimentation in your vehicle will determine the best setting but generally when seals and doors start to loosen - air leaks appear and 'fresh' seems to work best.

The best chance we have of minimizing dust ingression is to seal all potential gaps behind the front vents and drive with the air selector set to 'fresh', the fan on high and the air conditioner turned on.

Leak Sealing

The largest potential culprit in the air leak war are the rear doors on 4WDs. Rear doors are big, heavy and hinged and suffer continual movement and eventual misalignment. The very first thing to inspect and remedy if you are serious about keeping out dust is to fix poor alignment in your rear vehicle doors (not passenger doors but the cargo doors). Aligning doors can be a frustrating and time consuming exercise that firstly involves locating the bolts that hold the hinges and doors and then systematically making finite adjustments and rechecking until everything is shutting properly and sealing tightly. Components like catches wear over time and cease to hold the doors rigidly sealed. This is especially true where a spare tyre is bolted directly to the door panel and the additional weight and leverage increase wear and misalignment.

The sealing ability of a door can be checked by applying a bead of silicone grease to the entire face of the rubber door seal, closing the door and checking to see if contact against the steel car body is complete - evidenced by a trace of grease remaining on the car body.

A silicone grease or lubricant (made for rubber, not synthetic) can be applied to all door seals to allow movement and horizontal and vertical 'slipping' of the doors during travel. It keeps the seals supple and prevents damage to binding seals that create air gaps.

4WD's come in a variety of configurations from the dealer and additional holes can be supplied to allow for things like extra seating, baby capsules and cargo barriers. Lifting the carpet in a four wheel drive can reveal a plethora of potential holes that will allow air through. Often a simple bolt is all that is required to seal the leak. 11 seater Toyota troop carriers with a potential additional 8 rear seats and seat belts are real culprits where this is concerned.

Many vehicles come supplied with rear external vents, designed to allow air to flow through your 4WD while you hum around the pristine concrete plazas of Tokyo and Sydney. They also provide a massive passage of air through your car. Stop the air flow - reduce the dust ingression. We often temporarily tape these ducts up with quality duct tape when travelling long distances on dirt.

Car passenger doors are manufactured with small holes in the underside. These allow any water or condensation to filter back to earth and help prevent the build up of moisture and corrosion. It is important that they remain unblocked and free to drain - even in desert like conditions. However, under the door skins, ie: the trim on the inside of the doors, lurks a plastic layer that completely seals the dusty outside world from entering via these drain holes and via the window seals. These plastic sheets are normally sealed with a bead of 'Sikaflex' or some similar sealant and the degradation of this seal can allow large amounts of dust into a car. Mechanical repairs inside the doors or bad factory fitting are the usual causes of damage to this layer.

Canopies

Canopies provide a whole new set of parameters to deal with - virtually being a ute or tray back with a separate cabin attached and never designed with dust sealing in mind. Again the key is to maximize rear sealing and increase airflow from the front to enable positive air pressurization. Keeping a forward window open and then coming to a complete halt means all that circulating dusty air has the opportunity to invade and a forward located vent may be a better proposition than an open window.

Dust Deflectors & Wings and Things

Formula 1 cars have wings at the rear to hold them down on the racetrack and modern 4WDs sometimes comes equipped with a similar attachment to help create a swirling updraught at the rear of the vehicle and prevent traffic disturbed dust being inhaled in through the rear doors. Companies like Toyota don't spend millions on research and development fitting wing-things to 4WDs like the 100 series without a reason and reports are that they can work.

Reality

Dust inhalation in 4WDs is a real issue if you plan on covering hundreds or even thousands of kilometres on Australia's many isolated tracks. If you are engaged on long hauls through desert like conditions then dust is a fact of life. When you unroll your swag you will be bedding down in the 'red flour' and every bit of breeze will deliver a new coating of dust to your car, body and kit. A mental acceptance of this fact is essential if you are determined to explore the country's more remote regions (and most roads into iconic locations like Karajini or Cape York).

By understanding the fundamentals and sealing up the back end, pressurizing the vehicle and finding out what works best for your car (mostly either setting to 'fresh or recirculate') you can minimize the impact and reduce the ingression of dust.

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