The more air available in the combustion chamber, the more completely the fuel is burnt meaning more heat, and more force pushes the piston down. That equates to more power at the wheels.

It is possible to have too much boost. The engine is only designed to handle a certain amount of compressed gas inside the chamber when the piston has risen to the top. Besides, there's a point where there's more air than needed for the fuel - the extra energy used to pump that air in is not equal to the extra energy created by the engine.

So, what we really have is an air pump that is driven by burning fuel. The more fuel that's burnt, the faster the turbo goes.

Sometimes one of the bearings will wear badly and start leaking oil, there are a few signs of this issue. Blue smoke may be evident while the engine is running, the turbocharger may squeal (like fingernails on a chalkboard) and the engine may seem to have lost power. Since they're tuned to expect the full boost available from the turbo, when the turbo is underperforming, the engine will perform poorly.

The last cause of damage is water from river crossings. The turbocharger will get wet and if it's extremely hot, the water will rapidly cool the housing causing it to crack. River crossings can be done with a turbocharged vehicle but you MUST let the turbo cool before making the crossing, you should ALWAYS use a wading bra and you should only use enough power to get you through. How cool? As cool as possible. If you've been driving hard, let the engine idle for at LEAST 3 minutes, or better still 5 minutes before attempting the crossing.

After that, the key is to let it cool down before turning off the engine (or entering the water). The best way is to plan your journey so that for the last few minutes, you just drive gently. If that's difficult (say you live at the top of a hill) then let the car idle for a couple of minutes before turning it off. You could add an EGT gauge and see for yourself if it's too hot (figures for approx acceptable temps to come). Whilst not legal, you can buy and install a turbo timer which will do the waiting and switching off for you. With a little bit of time,two kits you can buy in Jaycar and a few extra components you can make the ultimate - an EGT-controlled turbo timer. There is no guide for doing this at the moment.

If you forget and remember just after you turned the engine off - just start it up again; this will continue to circulate the oil (and water, for those with water-cooled turbos) allowing it to cool down.

The other consideration to prolong the life of your turbo is to avoid using lots of power until the engine is warm (and thus the turbo is warm).

The intercooler has an additional purpose; think of it as insurance. If your turbocharger ever destroys itself, those parts that would normally be flung at nearly 200km/h towards your intake manifold will be directed towards the intercooler, which will catch most of the small particles and all of the larger ones. The remaining small bits shouldn't pose a major problem unless you're unlucky to have one caught on a valve seat as the valve tries to close and is jammed home as the piston reaches the top (TDC).

The effectiveness of the intercooler lowering the temperature of the charge air depends on several factors; including the ambient temperature, humidity, the efficiency of the intercooler and how much oil (from the PCV system) is inside the intercooler compromising its performance (get a catch can!). Catch cans help to remove some of the oil being pumped out of your crankcase's breather hose that normally is ingested and combusted by the motor.

Technically, the intercooler in our vehicle should be called an aftercooler. The term "intercooler" comes from the device that cools the airstream between (hence 'inter') multi-stage compressors - think of a turbo that feeds a cooler that feeds a turbo that feeds a cooler that feeds the engine. Since ours only works AFTER the turbocharger, it is rightly called an aftercooler. Either term is acceptable in practice as long as we understand what we're talking about!

You can replace most of your hosing with metal pipes to reduce lag. You shouldn't try to replace ALL of it. Some flexibility needs to be there so the engine can move. Make sure the pipe you use isn't smaller (inside) than the hose you're replacing.

For more information check out the wikipedia entry for turbo chargers at http://en.wikipedia.org/wiki/Turbocharger

Written by Old.Tony March 2012
Thanks to Tweak'e and DodgyPuzzles for proof-reading and corrections.
Updated 21 May 2012 by Old.Tony

Although most of the new model Navaras are rated to pull 3 tonnes (3T), there are variations, especially in the older models and the 2WD versions. You need to keep these limits in mind not only for safety reasons, but because insurers can - and have in the past - refuse insurance payouts based on a breach of the rules. They can also seek to recover monies from you if you were found to be doing something outside the legal limits.

The most important point to remember is the towball weight (read about this further on). When loading your Navara's tub, don't forget to add the towball weight to the vehicle - and stay under the vehicle's Gross Vehicle Mass (GVM)!

There are reductions in the GVM that apply to certain towball weights and these are model-specific. For instance, if you have a 2014 model 2WD dual cab and have a towball weight of 140Kg, you have to reduce the GVM figure from 2805Kg by 110Kg to 2695Kg and THEN do your calculations.

Here's an example. Your car is a D40 4WD auto dual cab that weighs 2500Kg (with bullbar, winch and ONE person), you want to tow a 1800kg van (180kg towball weight, so 60Kg has to come off the GVM) and you have 2 more adults (140Kg) plus about 200Kg of fridge, clothes and recovery gear. That's 2500+140+200+180 = 3020Kg - the car's limit is 2920Kg (2980 minus 60), so something has to go.

There are some important factors if you're towing 2T or more. First, not only does your trailer need electric brakes, it needs a breakaway braking system and, in NSW for now, it also needs a unit that monitors the breakaway system's battery! There's also a rumour about requiring reversing lights to be fitted - it may not be retrospective, but if you're planning on getting someone to do the wiring in your Navara, get them to add the reversing wire to pin 2 of your 7-pin or 12-pin plug! Check the wiring section below for more info on the connections.

For trailers under 2T, the generally accepted guide has been to use 10% of the trailer's gross weight. This means you need to balance the load around the trailer to achieve this.

For trailers over 2T (and up to 3T) manufacturers have been recommending some rather different ball weights - but always in excess of 100Kg.

If you don't have enough weight on the ball, the trailer will tend to fishtail (particularly single-axle trailers). This can be more of a problem when braking - a trailer that is already trying to swing sideways will happily continue moving sideways and around the tow hitch as the car slows, colliding with the car ('jack-knife'). You also need some additional weight so that you can maintain rear-wheel traction on loose/wet surfaces (particularly up hills) when trying to pull the extra weight. Also, if the towball breaks, you want the trailer to nose-down and hang off its chains rather than punching through the back of the vehicle!

If you put too much weight on the ball, you do little more than weigh the back of the car down. Your car's front wheels will feel lighter and braking in the wet or on loose surfaces will be considerably more difficult. Don't rely on weight distribution hitches to balance the car in this situation - reduce the towball weight!

Rather than go through a brief and unclear explanation, click here for an informative page (with some more discussion of why) that shows how to do it.

There is a tool that can be purchased from some caravan places that measures ball weight - but really, you won't need it often enough to justify the cost (my opinion).

Apart from balancing things so that there is enough ball weight, your trailer performs best when there's an equal amount of weight on both left and right sides and when the weight is as low as it can get.

The height of the weight is an important consideration when cornering or negotiating uneven ground. If there is too much weight up high, it can overbalance the trailer and cause a disaster.

Just as an aside: both terms are misnomers. The spring bars don't redistribute the weight and don't level out the load either. What they do do is alter the impact of that load - it all still rests on the ball, but the car is being twisted upwards at the rear by those spring bars to counter the rear-down attitude of the vehicle.

The ideal configuration sees the vehicle settle an equal amount on the front and rear. Before attaching the trailer, measure the height from the top of your wheel arch to the top of the wheel rim (or centre of the hub, as long as it's part of the axle and not the tyre). Do the same front and rear of the vehicle. Now attach the trailer and measure again. If the front has reduced in height more than the back, your WDH is twisting too much - back off the cams in the head a little, or let the chain out by a link. If the front hasn't settled as much as the rear, you can use another link in the chain or adjust the cam in the hitch. Try to get the front and rear settled within 5mm of each other.

There's a caveat (isn't there always) to using WDH devices. You can't take them on severe undulations. You shouldn't enter steep driveways with them. The issue is the angle of the vehicle to the trailer - including the roll angle. WDHs don't like much more than flat ground. Doing so for a moment isn't too bad, but the spring bars can be deformed badly and become ineffective. Before you enter that sort of terrain, remove them - and drive slowly.

Air bags in many utes (not just Navaras) have caused problems even when the vehicle isn't overloaded. The issue here isn't that the vehicle has been overloaded - it's that when the suspension suddenly compresses fully (eg steep causeway, large pothole, rivulet, speed hump, large rock etc) the air bag hammers into the chassis midway between the designed load points. This bends the chassis at that point and it's bye-bye car.

These devices also inhibit movement (flex) of the vehicle, particularly noticeable on rough terrain (eg off-roading). Because the springs can't compress as far, bringing one rear wheel over a hump in the road compresses the suspension until the airbag stops further travel that you normally would have had. This will both destabilise the vehicle and possibly lift the opposite wheel, losing traction (unless you have lockers).

With that said, people do install air bags and enjoy the on-road stability and assistance that they provide for the rear of the vehicle. It is vital that one never overloads the rear when using air bags, and it's fairly important to reduce the pressure in the bags when you've unloaded the vehicle. It should go without saying that paying attention to the road and slowing for sudden height changes is almost mandatory with these!

When being passed from behind, the biggest worry is being drawn toward the passing vehicle. To counter this, I always move a little to the side of the road - keeping in mind potholes and jagged edges - and I keep a firm grip on the steering wheel. With the large boxy freighters, I sometimes have to steer left a little, too. The faster they go past, the sooner it's over, so as they pull out, I'll slow a fraction to assist the maneuver.

Oncoming rigs usually cause issues with mirrors if you have those strap-on extended mirrors. If you're unlucky, the mirror will slam backwards so hard it will destroy your weathershield - there was a point (when I was using these mirrors) that I'd open my window and hold my mirror steady when I saw an oncoming truck.

Following large trucks on an outback highway in the darker hours (from just before sunset to after sunrise) can also be dangerous. A truck hitting a roo can smash the animal into broken pieces, and a hollow leg-bone will carve a nice hole in your tyre. Avoiding these obstacles might be easy if it were just your car, but if you're dragging 2+ tonnes of trailer, you can't throw the car around as quickly. Leaving a little room is helpful.

Vehicles over 750kg and under 2000kg can employ "inertia" (or "override") brakes on at least one axle. When the towing vehicle brakes, the trailer slides forward on a shaft that the towball hitch is connected to and pushes a lever (usually the handbrake) to activate the wheel brakes. This is often messy, and sometimes results in the brakes not being applied when you want them (like on steep descents). A trailer that locks its wheels and begins to slide on its own is dangerous - if you have this setup, try to make sure that the inertia coupling can't lock the brakes at maximum compression. You should be able to activate the handbrake by pulling it further back than the inertia part travels.

Vehicles over 750kg and under 2000kg can also use electric brakes on at least one axle. These are activated by the tow vehicle's brake pedal via a "brake controller" which come in various types (discussed in the next section). You need to make sure that the electrical connection to the trailer is regularly checked - easy to do, because the brakes hum when they're working, so just give the controller's actuator arm a squeeze and have someone listen at the trailer wheels.

Vehicles over 2000kg require electric brakes on ALL wheels and also need "break-away" brakes. A retaining wire (not electrical, but strong enough for the task) needs to be linked to the tow vehicle, and the other end is attached to a switch. A battery on the trailer is charged by the tow vehicle (or if unused for lengthy periods, you need to keep it on a charger - consider solar!). This battery will, when the switch is activated, power the trailer's brakes bringing the trailer to a stop and holding it for 15 minutes. As mentioned earlier, NSW law now requires drivers with breakaway brake systems to have a monitor installed that shows the driver the condition of the breakaway system's battery.

Some people advocate simplicity over function and when towing a couple of tonnes, this can cause issues. You might be happy to live with them - I wasn't (1.8T caravan).

I initially started with a RedArc "proportional" brake controller that really wasn't proportional at all. You'd put your foot on the brake and a constant amount of current was supplied to the trailer brakes - even if you were just lightly coming to a stop, the trailer would haul you up harder. If you had to stop in a hurry, the trailer would not contribute enough to the braking and would keep pushing you forward.

I moved to a Tekonsha Voyager proportional unit which WAS proportional but had a manual setup. Every incline changed its configuration - no good for driving the vehicle in any mountainous region. If you set it up for level ground (as per the instructions) then it would not bother working on an ascent, and would over-exert itself on a descent.

The ultimate brake controller - and the one I have now - is the Tekonsha Prodigy P3. Fully automatic and adjusts for inclines on its own. Guardian, Hayman Reese and others don't come close (and I am not willing to test them any more - I have the unit that works like these things are supposed to).

The way the typical electric brake works is rather simple. The brakes in a trailer are usually drum brakes. Attached to one of the brake pads via a lever is an electro-magnet. When activated, the magnet pulls against the inner face (where the wheel studs mount) and grips depending on how much power is applied to the magnet. This force pushes the drum brake outwards. Simple and effective.

The wiring that you install has to handle this load. Choosing some light cable because it was on special will cause issues later, particularly on long downhill runs like Mt Ousley, Mt Victoria, Alpine Way, Bulli Pass, Cunninghams Gap, Moonbi, Nowlands Gap and many others. Thin cables carrying a constant current can heat up - sometimes to the point where the insulating jacket can melt, causing a short-circuit. Apart from the danger of fire, it also removes your trailer brakes when you need them the most!

Don't risk it. Use cable that is rated for much more than the load - for our trailer brakes, we have 8Ga cable installed (4mm wire diameter). Guarantees to not get warm when the brakes are held on, and holds its voltage reasonably well over long runs. Buying less will get you less!

Additionally, if you're towing heavy (2T+) you'll need a 12pin flat plug, with pin 8 supplying power to charge the breakaway battery, pin 9 for the breaksafe monitor and pin 10 for an earth return.

Those are the exceptions. Driving through a muddy forest trail at night we rarely exceed 30km/h. Driving for economy we'll hold it at 95km/h despite available speed limits of up to 130km/h.

Between sunset and about an hour or so after sunrise we tend to do things more slowly - not just in the outback, but even in semi-rural areas. Animal strikes aren't pretty, especially when you round a bend and find a large group of kangaroos having a community gathering in the middle of the road! It's important to point out that the "roo whistles" you can buy in auto parts stores don't work well below 55km/h, so if you have to slow down that much, you might consider slowing some more!

Slippery surfaces have several possible pitfalls awaiting the vehicle but even moreso when towing, because if the trailer lets go, there may be no stopping the inevitable slide or impact. Reducing the speed can prevent this altogether. It's particularly dangerous downhill, where the trailer would be quite happy to overtake the car! Use your brake controller's adjuster to reduce the braking pressure of the trailer. If you're using something like a Tekonsha Voyager, Guardian, Hayman Reese or Redarc brake controller, go even slower still - these units will happily lock the trailer brakes on a steep descent - some are not even proportional, and those that are (Tekonsha Voyager) don't automatically adjust for the incline.

Washouts are also a problem. Travelling on some outback roads you'll sometimes find what look like small gullies at the edge of the road surface. Consider these when you see an approaching truck - you have to cross them, so slowing right down to approach them at a gentle pace makes more sense than blowing every tyre on the left side. Moving your vehicle off the road is nearly vital. Let the truck have the road - a large B-double has a lot of wheels that flick up a lot of stones.

When you encounter variations in the terrain, these forces change. You may have a WDH and need to enter a steep drive to get into a service station for fuel, or clamber over a sharp drop to get into an area. Don't delay in these areas and if you know you're going to have to stop in an awkward position for some time, disengage the WDH so that it doesn't deform under the constant load.

Encountering large variations in terrain at speed is different. Your WDH may not care about a large change experienced over a fraction of a second, but hauling a heavy trailer into a causeway without slowing can cause major problems. While your vehicle is stationary, you might measure your towball weight to be a certain amount, but when moving at speed and encountering something like a causeway, that weight could be magnified dramatically (and the faster you travel, the more the magnification). This could result in chassis damage at worst, or significantly affect steering and braking.

These impacts are also one of the causes of shock absorber damage. Not as much from internally-generated heat like you'd see from corrugations, but from bending the shaft! The suspension does allow some fore-and-aft movement of the axle and a sudden movement accompanied by a large amount of force could translate into a bending motion causing the shaft of the shock absorber to rotate around the bottom mount before it compresses. You'll know it's happened - it'll be like you have NO suspension at all. If that happens, the only real thing you can do is remove the shock absorber and continue slowly to the next town.

It becomes even more important that the driver take breaks and is comfortable while driving - there's no joy in trying to drive long distances if you're cramped or otherwise distracted.

It's become our practice to take breaks when possible, even if it's just to grab another drink, or take a quick walk around and see if all the wheel hubs seem to be around the same temperature.