By Paul Abelson, senior technical editor
The final steps to 10 mpg involve fluids: oils and greases, coolants and additives. While engineering of the trucks and components makes up the largest percentage in fuel savings, it will be these final few small steps that help OEMs achieve the leap to an industry average 10 mpg truck.
Fluids have a fixed volume but no fixed shape. They flow to conform to the shape of their container and are pumpable. They have mass, volume and viscosity, a measure of how a fluid flows, measured at varying temperatures.
To understand viscosity, imagine drinking liquids through a straw. Water is easy, requiring little effort. A thick shake flows more slowly because it has more viscosity. It requires more effort.
Think of the suction through the straw being like the amount of effort required from engine pumps and gears turning in oil. The more viscous or thicker fluids require more effort. That translates to more fuel burned.
For years, the industry standard heavy-duty engine oil has been 15W-40. The W number indicates viscosity under extremely cold temperatures of 5 degrees down to minus 4 degrees in various SAE tests. The second number shows the oil’s viscosity when tested at the industry standard 212 degrees.
So, 15W-40 oil will flow enough to lubricate when cold and will stay thick when heated to water’s boiling point, close to diesel operating temperature.
We’ve seen many recent improvements in the properties of engine oils. All have improved ability to adhere to metals, to withstand high pressures and to stand up to high temperatures. Synthetic oils in particular require less effort to flow, especially when cold. Engines operate well on thinner newer oil.
Some oil companies promote their 10W-30 petroleum-base oils and 5W-30 synthetic-base oils as fuel-saving alternatives to 15W-40. In SAE/TMC tests, mineral oil saves up to 1.8 percent, while the synthetic 5W-30 was about 4 percent better. For a 100,000-mile-a-year truck getting 6.5 mpg, a 4 percent savings is about 615 gallons. At more than $4 a gallon, that’s about $2,500 a year.
The same principle applies to drive trains. Lighter synthetic lubes require less energy in gear boxes and differentials. Conventional oils have to be thick to resist thermal breakdown. Boiling off volatile fractions of lubricants leads to varnish formation and thickening over time.
To overcome these problems, viscosity improvers, dubbed VIs, were developed. Improvers are polymers added to thin oils. When heated, they cross-link and thicken the oil. Synthetic base oils are more uniform with properties that can be engineered and manufactured rather than refined and treated. They require fewer viscosity improvers and flow more consistently.
Trucks with full synthetic lubricants in the engine, transmission and differentials will save about 3 percent of fuel. When lighter synthetic weight oils replace heavier, higher viscosity mineral oils, savings increase to around 5 percent.
Additives are available for oil, but there are two schools of thought on treating. The major oil refiners claim that their products are carefully blended to meet or exceed industry standards for everything from cold weather flow to prevention of deposits on piston rings. Anything that alters the delicate balance of base oil and multiple additives used in blending could create deposits or alter the oil’s properties.
But there are tens of thousands of truck owners who have used oil conditioners for years with no adverse effects. Some additives contain friction modifiers, chemicals that reduce internal friction in components like engines and drive trains. Testimonials claim they are effective, but it’s still a good idea to look for impartial SAE/TMC testing results.
Another power-consuming fluid is coolant. Today’s typical coolant is a mixture of de-ionized water and glycol-type antifreeze, usually close to 50 percent of each with small amounts of additives.
The water in both conventional coolants and extended life coolants (ELCs) is an excellent heat transfer medium. It carries excess heat from cylinder liners and heads to the radiator. In turn, heat transfers to the air flowing through the radiator. But water is a limiting factor.
Diesel engines operate more efficiently at higher temperatures. Pressure caps raise coolant’s boiling point, but water can still boil and form steam pockets that both block coolant flow and allow hot spots in the engine.
To get higher operating temperatures, Evans Coolants developed a line of waterless coolants. Because the glycol base has a boiling point more than 100 degrees hotter than ideal engine temperature, no pressure cap is needed, reducing coolant leaks. Without water, liner pitting, scale and other conditions are no longer problems, so no additives are needed.
With a 215-degree thermostat and the cooling system modified with the engine control module set for fan on at 230 degrees, fan off at 217 degrees, engine de-rating at 235 and auto shutdown at 240, the fuel savings are dramatic.
In SAE/TMC tests with fans operating continuously (for control purposes), fuel economy improved by 3 percent. Since fans can use 50 to 75 hp when on at high, and draw 30 to 35 hp at cruise, fuel economy with fans operating is even better. With fans under ECM control, total savings are as much as 7 percent.
Fuel additives are not just to prevent winter problems. Used year round, most well-known brands will maintain your fuel system in like-new shape, but they will not increase mileage. Two products from TMC members do, in fact, improve fuel economy. Combustion Technologies’ Clean Boost has been tested by the Southwest Research Institute, and Dipetane was tested by Claude Travis Associates.
In independent testing, both products demonstrated about a 3 percent reduction in fuel use.
Three percent is 451 gallons at 6.5 mpg, or close to $2,000 a year. Both suppliers provide testimonials from fleets claiming even greater savings in real-world use, but the 3 percent achieved in controlled tests is still in impressive number.
If you look at the progress already made and now under development, the 10 mpg truck may be just around the corner, if it’s not here already. LL