Two mechanics, who requested anonymity, warned prospective diesel car buyers of the often higher servicing costs and the large costs that can arise from neglected servicing. "A work colleague complained of a $600 30,000km service charge on his car," one mechanic said.
"This was partially due to the need to replace the in-tank filter. Diesel engines even before common-rail was the norm had far more stringent filtration requirements for fuel and engine oil than petrol engines. "Common-rail systems can have fuel pressures in excess in of 30,000psi, in the old imperial units, and will not tolerate contamination of fuel.
"In addition, diesel engines produce far more soot and oil contaminants than petrol engines and have higher bearing loads making it very important to use quality oil, filters and coolant. "I guess the moral of the story is do not take short cuts with servicing and stick rigidly to recommended service intervals."
Another mechanic said that if owners carried out regular servicing and the fuel system water trap was drained out at each service and the fuel filter replaced these problems would not occur. "It all comes back to regular servicing with a reputable service agent," he said.
"Yes it is more expensive to service diesel vehicles but when maintained I feel you have a longer service life than with petrol engines. "I do feel people are not properly educated when it comes to diesel engines. "The average mum and dad are still confused at the pros and cons of diesel vehicles."
RACQ vehicle technologies manager Steve Spalding said their annual running cost surveys showed small diesel cars were more expensive than their petrol counterpart over a five-year period. "In general, fuel costs are lower but servicing costs are higher," he said.
"The diesel versions usually have a higher initial purchase price therefore impacting on the overall ownership costs." He said servicing was more critical to a diesel, particularly to the fuel system such as filters.
Spalding also confirmed that diesels require expensive high-quality diesel-specific oils and neglecting to properly service a diesel vehicle could lead to more costly repairs. "Our advice is to stick to the servicing schedule and only use quality oils and parts to the required specification," he said.
"As routine servicing generally costs more, consider this prior to purchase so that there are no surprises when it comes to service time." One of the mechanics also warned of buying second-hand diesel vehicles because buyers would not be able to confirm whether the original owner had kept to manufacturer specifications for servicing.
Spalding said poor quality fuel also was a problem for modern common-rail diesels, particularly with water and contamination, while older diesels had some level of tolerance. Owners wishing to use biodiesel should check with the vehicle manufacturer as their warranty may be affected if a component failure is found to be linked to non-recommended fuel, he warned.
Diesel contains oil that lubricates the internal parts of an engine. If misfuelled with unleaded petrol which does not have any lubrication, it can lead to engine scouring and a bill of up to $10,000. Even if the engine isn't started, the fuel system will have to be flushed and could even need replacing.
Misfuelling is estimated to cost more than 800 million a year in Britain. While no figures are available for Australia, car clubs estimate that thousands of motorists misfuel diesel cars each year.
The mistake occurs because most unleaded petrol nozzles are slightly smaller than diesel nozzles and will fit in the filler neck of a diesel vehicle. Only a few vehicles have safety features on their fuel tank filler neck to prevent using the wrong fuel.
However, there are aftermarket devices available now which require the larger diesel nozzle to open a safety valve in the filler neck. One of the latest is the British Diesel Key which replaces the filler neck and cap. The lockable device also helps prevent fuel theft.
It costs $120, can be fitted in minutes and fits most European and some Korean vehicles. Australian distributor Alex Irvine said several car companies here were interested in fitting them prior to sale.
He said if fleet operators needed a special or custom fit, they could re-tool to make them, but there is a minimum order of 1000. Despite the negative aspects of diesel cars, Spalding said there were many benefits such as good fuel economy, lower CO2 emissions, higher mid-range engine torque suited to a wide range of driving conditions, greater towing capabilities and longer engine life.