Petrol or Diesel 4WD?

The debate over which is the better fuel, diesel or petrol, has raged since the inception of the automobile and loyal devotees of either flavour will loudly protest one over the other.

Both fuels have inherent benefits and flaws and each have their place for 4WD and touring applications. These days, claims of massive superiority of one type of fuel over the other are mostly redundant as technological improvements in both styles of engine make rapid advances every year.

bulldozer and hotrod
Characteristics

Typically in four wheel drive applications - older diesel vehicles were considered sluggish and truck-like while petrol was considered less reliable in harsh conditions and lacking torque (basically - 'pulling power').

Today's higher revving diesel engines with turbochargers and computer enhancement and their petrol counterparts - with better low end power aided by refinements such as traction control and engine management, are bridging the divide and becoming measurably closer as far as performance is concerned.

Many factors should be considered when choosing which engine will best suit your particular situation and care should be taken to assess which of those factors affects you the most. Driving conditions and environments can change on a daily basis. The 4WD that launches a boat in soft sand on weekends may be used as a city commuter for the remainder of the week, meaning - any vehicle choice is likely to require some sort of compromise.

Price

There is a wide gulf between the price of a new diesel car and a new petrol car. This is caused mostly because of more expensive manufacturing techniques in diesels which require heavier duty components for their high combustion engines. This relates directly to a heavier roadside mass which in turn may require more robust steering, suspension and associated components. Many larger 4WD's are sold with turbochargers to help move diesel vehicles into the quicker accelerating realm of petrol.

Maintenance

Petrol engines tend to run longer between services (although modern advances in diesel technology are dramatically reducing this gap). Part of the reason is the cleaner burning nature of petrol. The parts required for servicing a petrol car will generally be cheaper as oil quantities are smaller and filters fewer and cheaper. The offset is that diesel engines have, by nature, a longer life than petrol, typically 30% or more, meaning a good service schedule will see a diesel outlive a petrol by some years - given the same mileage.

Fuel Economy and Availability

Diesel still remains the working fuel of choice for mining, agriculture,road transport and rail industries, meaning it is available nationwide. There are areas in remote Australia where fuel sniffing is a major social problem and standard unleaded or premium petroleum is simply unavailable. The alternative is often aviation fuel at hugely inflated prices. While this occurs in mostly isolated communities it is still a consideration if you intend doing large distances through central Australia.

Virtually all heavy earthmoving and agricultural equipment runs on diesel and this equates to a generally smaller gap between diesel and petrol in rural areas. This can make a difference if your vehicle is primarily run in the metropolitan area or in rural and remote districts. Essentially running a diesel in the country is cheaper than running one in the city (in relative comparison with petrol). It still remains that diesel is more expensive than petrol at the pump (even though it is less refined and should be cheaper!)

However, the offset is that diesel vehicles are normally more efficient than petrol and burn less fuel given the same task, generally considered to be around 20% better and upwards. Simply, your 100 litre tank full of diesel fuel will travel further than your 100 litre tank of petrol.

Virtually all common testing and experience suggests that a petrol engine will be cheaper to run and maintain overall than a diesel engine.

Maintenance

Safety

Many people carry large quantities of fuel when traversing iconic tracks such as the Canning Stock Route, going as far as towing trailers with 44 gallon drums of fuel on board. In the ultra hot environments of central Australia carrying this much volatile unleaded fuel requires extra diligence in keeping it secure and avoiding issues with its highly flammable nature. Diesel, on the other hand, is much less volatile and makes for a much more stable travelling companion. Another often neglected fact is that exhaust temperatures of petrol are much higher than that of diesel and have far greater potential to start grass, spinifex or crop fires. Farmers who experience sporadic summer bans on all vehicle movement in their wheat paddocks will appreciate this fact.

Comfort

There is nothing worse than spending a day covered in diesel after refueling at a leaking, poorly maintained roadhouse in the middle of nowhere. Diesel's base nature is close to oil and it is a dirty, smelly, insidious product that has no place being handled in the 21st century (except that it does lots of things really well). Diesel engines tend to run noisier, make more smoke and operate less smoothly than petrol engines, although as ever, these characteristics improve every year and modern diesels really have made huge leaps forward.

Performance and Workability

This area of comparison is the one that provides the greatest divide between the petrol and diesel camps. The petrol mob will shout loudly from the ramparts about the user friendly benefits of petrol and it's cheaper and sportier performance while the diesel opposition will point out the workman like quality of diesel and its ability to pull a bulldozer through a swamp (sort of).

Both attitudes have their place. Lugging a heavy diesel around shopping centres and through traffic cannot compare to driving a zippy, quick accelerating petrol car around a city. Likewise when it comes time to purchase the car, the extra dollars involved can make the buyer wince with envy as they eye off the less expensive and cheaper running petrol jobs.

However, take a diesel up a steep, rock strewn hill, put it in first and sit back while it just tractors on up, refusing to stall. Take it over the hill and marvel at the way the engine-braking capabilities, in low range, magnificently control the descent and the benefits of diesel really begin to shine.

When it comes time to cross a bonnet deep water crossing (providing an airtight snorkel has been fitted), the diesel punches through, virtually submerged, while the petrol engine often splutters and dies as water contacts spark plugs and distributors.

Hook up a caravan, fifth-wheeler, camper trailer, horse float or another car for that matter, fill the 4WD with 200litres of fuel, load up the roof rack with a dinghy, jam-pack the rear cargo section and then let the torque of the diesel get all this additional weight up and moving with relative ease. No other type of engine/fuel combination can accomplish these types of loads with the same level of working performance. This is especially true when the car is fitted with a turbo.

Petrol engines make their mark when you reach into your wallet and when you are travelling relatively light and it is time to pull out and round up a road train. The quick responsiveness of the lighter petrol vehicles is easily appreciated. Driving on firmer sand and gravel is bags of fun where petrol vehicles can provide rally like performance in a bigger package.

And finally there is something nice about sitting behind the wheel of an idling petrol 4WD and wondering if it is still running - because you are accustomed to driving diesels and you can hardly hear or feel the petrol motor.

Diesel Pros
  • Work-like torque curve for towing
  • Highly resilient to water crossings
  • Tractor like control in difficult terrain
  • Longer fuel range
  • Safer fuel with a lower ignition point
  • Possible 30% longer engine life
  • Great fuel availability
Petrol Pros
  • Cheaper purchase price
  • 'Sportier' performance
  • Cheaper to run
  • Cheaper to maintain
  • Smooth and quiet running
Summary

On paper the petrol engine reads like a hands down win over the diesel and why not? It's going to be cheaper to buy, save some real money in the long run and be a nicer proposition to drive and own. If we only ever drove in the metropolitan area we wouldn't even consider diesel.

However we don't live in the metropolitan area. We drive hundreds of kilometres out of our way to avoid big towns and cities. For serious off-road driving in remote Australia, especially while towing heavy loads - we choose to drive a diesel 4WD.

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