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Diesel turbo failures
Why is it that petrol engines seem to last so much longer than the average turbo-diesel? The answer is anything but simple. Try as I may, being simplistic about this issue isn’t going to help, so here I am going to get a bit technical. So, if you own or are planning to purchase a turbo-diesel vehicle, understand the pitfalls because some are very costly. I am not advocating staying away from diesel engines but rather an understanding of them will not only prevent huge repair bills in the future but also enable you to get the long life that a diesel engine can deliver if treated correctly.
In 2000 owning a Mercedes 290 GDT, I experienced an engine failure which resulted in a huge learning curve for me. It happened on a trip through Johannesburg so I called Steven from Steve’s Auto Clinic. Having more experience with diesels than anyone else I knew, I felt confident I was in safe hands. To cut a long story short, a blocked air filter had caused an excessive exhaust gas temperature which caused turbo and injector damage. Two years later I purchased another used 290 GDT. I remember the famous quote, ‘Those who do not learn from history are condemned to repeat it’. I visited Steven and again I was on a learning curve. In just two years problems with damaged turbochargers in thousands of vehicles had spread from turbo failures to cylinder heads as well. I wanted to know why.
Steven uses an effective analogy. A new vehicle is like a healthy child, fit and energetic. The child’s body is like the vehicle’s engine. Once a child becomes a teenager some begin to smoke, drink or both. The body begins a path of deterioration and becomes diseased. By forty, the equivalent of forty-thousand kilometers, doctor says, “Stop smoking!”. So the smoking is stopped. Is the adult suddenly healthy because a bad habit is kicked? No. Damage has already been done.
A new vehicle drives energetically out of the showroom. In the case of a diesel engine it is often mishandled recklessly, like the teenager on a binge. Driving a turbo-diesel at full power for long periods, hauling heavy trailers up steep hills at full power, hour after hour of speeding down to the coast at 150 kph. That’s how to abuse a turbo-diesel. These engines are not designed to work this way and it damages them! So if you want your vehicle to perform these tasks, buy a petrol! Petrol car engines are more suitable than turbo-diesels for running at full power over long periods.
The advice on fitting exhaust gas temperature gauge early in the vehicle’s life cannot be over emphasized. Drivers inadvertently abusing the engine, driving it in a manner which over-stresses it will be warned by the gauge and buzzer. This is one of the problems with buying a used turbo-diesel. Fitting an EGT gauge after the vehicle has covered 50 000km is like a forty year old quitting smoking. The damage has been done. Not smoking at all is the most desirable: never abusing the engine because a gauge is telling you that you are. It’s a bit like a government health warning, but instead it reads, “RUNNING THE ENGINE LIKE THIS WILL SERIOUSLY DAMAGE YOUR WEALTH”.
Diesel engines are happiest when driven on or close to the revs that produce the highest torque. At higher revs, torque drops off and while power increases so does the temperature generated. The result is high fuel consumption and high engine temperatures. This is why above 140 kph most diesel engines will consume about as much fuel as a similar petrol vehicle. At this speed the petrol engine is happiest, revving high and burning its fuel efficiently, while a diesel is at high-stress, running hot and burning fuel inefficiently.

Things have much improved over the past couple of years. If you are contemplating a used turbo-diesel built before 2003 then what I have described here is most likely the case. Thankfully almost all diesel engines built today are equipped with sensors that will cut off fuel in the event of over-stress. This may mean that newer vehicles may not appear to perform as well as similar older versions, but this is not true: The newer engines are so much better at protecting themselves from abusive users.
So when considering a new or used vehicle, think about what kind of driver you are. If you are towing a heavy load, choose a petrol. If you want the economy of diesel, decide now that long stretches at high speeds are a thing of the past. If the vehicle is used, do a diagnostic test to see if damage has been done and if it’s new, fit an EGT gauge without delay and reset the diesel pump on an active dyna to limit the combustion temperatures before damage is done.

Typical turbo waste-gate damage caused by excessive exhaust gas temperatures.

A cylinder head showing the three valve seats and the pre-combustion chamber.

A damagaged pre-combustion chamber. The change in shape of the aperture and the cracks cause severe reduction of power output.

Turbo-charging a non turbo engine
Unlike a petrol engine a diesel engine is ideal for turbo-charging. Everything is already there: the compression ratios, the strengthened block, conrods and pistons. So it makes adding a turbo a simple matter of plumbing it in. Sounds too good to be true? Well is it, almost. The trouble is, not all diesels can cope with the added pressures caused by a turbo-charger when at full boost. One such engine is Toyota’s ubiquitous 4,2 six-cylinder 1HZ engine found in their Land Cruiser 70-series, among others. Among engines, this is the one renowned for being virtually indestructible, but the best way to bust this engine is to add a turbo-charger to it. This is why so many engine specialists have developed turbos for the 1HZ and found returning customers with unhappy faces. It is all because they all boasted that their’s produced the most power and those who were right, regretted it the  most. The culprits are the pistons of the 1HZ. The crown of each piston is unusually thin, to save on weight, I suppose. The thin crown is soon blown apart by high boost pressures. The answer is low boost turbo-charging, or replace the pistons with heavier duty ones, which because they are not available off-the shelf, is very costly, and then add a normal boost turbo-charger. I have selected to try Steves Auto Clinics low-boost turbo-charging option for my own 1HZ powered Cruiser 105. (Any reports I have will be viewable on www.4xforum.com. Look under the ‘articles’ section)
So when considering adding a turbo to a normally-aspirated engine, beware of taking into consideration which conversion produces the most power, but instead look at the conservative approach that will tend to be the best, because it will likely mean that the developers have considered cooling and longevity more closely.

Loading capacity
When travelling through remote or unpopulated areas; food, water, fuel, tools and camping equipment have to be carried. Therefore your vehicle should have a large enough loading capacity in terms of volume and weight. Water weighs one kilogram per liter and fuel almost as much. Heavy duty suspension should be fitted to those vehicles asked to carry loads close to their limits over rough ground. Heavy duty shock-absorbers will also assist.
When selecting a 4×4, it is worth asking how much weight can be carried on the roof. Unfortunately I have rarely seen this specification published in a sales brochure, because so often it is alarmingly low, so this information may be hard to find. The range of weight to be carried ranges from the lowest in vehicles such as old Range Rovers at about 50kgs, Land Rover Defender at 75kgs and up to 200kgs on a Mercedes G-Wagen and Nissan Patrol. (Specs not verified)
Loading any roof rack too well forward will cause overloading of both roof pillars and front springs. Structural failures from overloading show themselves in the form of cracks in the windscreen and fading shock absorbers. If you have a winch, bull bar, power steering and air conditioning fitted, your front springs may well be pushed beyond their design limits. Overloading a vehicle’s springs will quickly result in serious structural failures in rough terrain including chassis breakage.
Disc Vs drum brakes
All-wheel disc brakes are an advantage on and off-road. Apart from not being affected by water, like drums, they operate effectively in reverse. This is where the disadvantage comes, which can be significant off-road, when drum brakes are fitted on the rear wheels. Picture the following situation: A vehicle stalls while moving up a very steep climb. The vehicle must be secured before the clutch is depressed and the engine restarted or the reverse-stall manoeuvre performed. The foot brake and hand brake are used to hold the vehicle. With the drum brakes on the rear axle doing almost all the work, and with a stalled engine and no brake-boosting assisting the effort, it may be impossible to secure the vehicle with brakes alone. In this case the vehicle must be left in gear and rocks packed behind the wheels to assist the braking effort before the clutch can be depressed.
Although all drum brakes are less effective in reverse than discs, not all drum brakes are totally ineffectual in reverse. Generally speaking, the older the vehicle, the worse they perform.

After driving through deep water, water can become trapped in brake drums making them ineffective. Sand can also collect in drum brakes damaging the shoes.

Vehicle range and payload
A vehicle required to undertake journeys into unpopulated areas needs a good range to be effective. Because payload can be converted into range by carrying more fuel, either an economical engine or high fuel tank capacity and payload is required to give a vehicle a good range.
I suggest a range of no less than 1000 kms between fuel stops if you are planning to create a good expedition vehicle. Few standard vehicles will cover this distance without additional tanks or Jerrycans. Auxiliary fuel tanks are discussed in Chapter-3.

With many pickups and some stationwagons 4x4s, the spare wheel is carried under the load-bay. By fitting a rear-wheel carrier, like this one by IEF Engineering, a large fuel tank can now be put in its place, low down keeping the centre of gravity low.

Jacking points
One of the most useful auxiliary items for the vehicle that is going to drive off-road is the high-lift jack. It requires a suitable flat jacking surface on the vehicle for efficient use. Modern designs tend towards curved rounded body shapes and rounded bumpers. If you are purchasing a new vehicle and intend to take it off-road, ensure that the bumpers are adequate in both shape and strength for use as jacking points. If not, suitable adaptations can be made so that a high-lift can be used with the vehicle. These modifications are fitted by off-road vehicle fitment specialists.

Wheel rim size
The size of the wheel rims fitted to a vehicle has a significant effect on its off-road ability and suitability as an outback tourer. Many new 4x4s are delivered with 17, 18 or even 19-inch wheel rims. Low profile tyres found on large rims are a significant disadvantage off road, for three main reasons:
When dropping the tyre pressures to increase traction or flotation, with a low profile tyre, the percentage increase in footprint size gained by the reduction of tyre pressures is less, so much so that it can make almost no difference and the vehicle performs as if riding on tyres at normal pressures.
Secondly, low profile tyres are damaged more easily as are the rims.
Thirdly, in remote areas, tyres damage, which is one of the most common cause of a failure or disruption of a trip, can cause it to halt altogether because in these areas, replacement tyres larger that 16-inch are extremely difficult if not impossible to find. In this case, you could find yourself utterly stranded.
In my view, 16-Inch wheel rims seem to be the most ideal for an average 4×4. 17” is acceptable, but for the third point