Operators of heavy-duty trucks know from experience that diesel fuel represents the single largest outlay of cash, typically running between 35 and 40 per cent of running costs.

Electronic engines and design improvements have certainly helped to reduce those figures. Over the course of a year, even a minor fuel economy improvement can show substantial savings to your monthly fuel bills. That’s where semi-synthetic and full-synthetic oils come in.

There are many different brands of engine lube oils now on the market. Since all must meet standards set by the Society of Automotive Engineers, the American Petroleum Institute (API), and the American Society for Testing and Materials, there really is little difference between the good and the bad.

That being said, there are some minor differences in additives.

Currently CH-4 is the highest level of oil performance defined by API for modern low-emissions, heavy-duty, direct injection four-stroke cycle diesel engines.

Extended oil-drain intervals and the retention of combustion soot place severe demands on today’s quality lube oils. Synthetic lubes – even after they have been well-used and are laden with soot – outperform conventional mineral oils with their additive packages.

A wide number of controlled-engine dynamometer tests have shown that by dramatically reducing engine component as well as drive-train parts friction, synthetic oils can cut fuel consumption by as much as three or four per cent.

Heavy-duty, electronically-controlled diesel engines require an oil that can handle increased soot levels produced by retarded-injection timing – a byproduct of complying with the U.S. Environmental Protection Agency exhaust emissions limits.

Coupled with higher top-piston ring location, engine oils face the daunting task of dealing with significantly increased soot levels, while also needing to protect against acidic corrosion.

Synthetic oils fill both of these roles, in spades.

There are a number of oil manufacturers that do claim that their premium 15W-40 heavy-duty engine oils, in combination with the latest additive technology, can rival synthetics in both protection and cleanliness.

Engine tests show synthetic oils, thanks to their ability to maintain viscosity even when dirty, can minimize soot agglomeration – or clumping – to achieve a fuel saving of between 1.8 per cent and as high as 2.83 per cent.

Coupled with the use of synthetic oils in the transmission and axles, a further fuel saving of between one and two per cent is attainable.

This friction reduction is possible because synthetic lubricants are manufactured from pure hydrocarbons, which are free from the impurities present in all mineral oils. It’s these impurities that boost friction between molecules, impeding both flow and performance of mineral oils.

Operators opposed to spending the extra dollars for fully-synthetic lube oils may choose instead to use semi-synthetic, or hydro-processed, base stocks.

As the combustion soot levels increase, semi-synthetics see increased viscosity at a much faster rate than a full-synthetic lubricant.

Consequently, truckers seeking extended service intervals – both based on time and distance – while also boosting profitability of their rig should look to full synthetics.

Maintenance costs for changing both oil and filters, conducting scheduled maintenance, as well as disposing of oil and filters, are also reduced with these ultra-clean oils.

It is worth spending a little more on a top-notch filter mind you, if you do plan to extend your oil drain intervals. A synthetic-media filter will ensure increased structural integrity compared to that of a conventional paper filter design. This will reduce your oil pressure drop as the filter becomes plugged with the gunk it pulls out of your engine.

Caterpillar, Cummins, Detroit Diesel, Mack, Mercedes-Benz, Renault VI, Volvo and Scania are all testing extended oil-drain intervals using new synthetics.

So far, fleets have been able to push intervals to anywhere from 60,000-to-100,000 miles using synthetics.

The average fuel economy benefit they’ve discovered when used in the engine, transmission and axles, ranges between 3.1-to-4.2 per cent, depending of course on the truck evaluated.

If we were to assume that a heavy-duty tractor was averaging six miles per gallon while running 100,000 miles per year, total fuel consumption would be 4,404 gal/year.

If fuel costs were 60 cents/litre, in a year the fuel bill is approximately $10,000. A simple switch to synthetic lubes – and the resulting three per cent gain in fuel efficiency – would save 500 litres of diesel.

In the case of a single vehicle, that’s about $300, but in a 500-truck fleet total we’re talking $150,000. And remember that’s at the low end of the scale.

If you realize a 4.2 per cent fuel bonus, that becomes a savings of 700 litres and $420 per year, per vehicle.

That’s $210,000 for that same 500-vehicle fleet. n