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In 1998, heavy-truck fuel economy averaged 6 mpg. Today, with more trucks on the road, hauling bigger loads, it just tops 5 mpg, says the U.S. Department of Transportation.

No wonder fleet operators are looking hard at aerodynamics, truck maintenance and driving habits, as described in last months column. Theyre also wondering if they can wring some extra mileage from lubricants.

The benefit doesnt need to be much. For the trucker putting 120,000 miles a year on his 18-wheeler, even a 1 percent increase in fuel savings is worth chasing – its 240 gallons a year. With diesel now costing $3.50 to $4 a gallon, that keeps almost $1,000 in the operators pocket.

Lubricants used in heavy-duty trucks can contribute that much to the fuel economy equation, and everything from wheel-bearing grease to gear and transmission oils to engine oil can play a part.

First, look at wheel-bearing grease. This has changed over time to a lighter, more efficient product with reduced friction in the bearings. Chassis grease is also more effective in providing protection to parts in contact with each other. Their contribution to fuel economy may be minimal, but these greases add to equipment uptime and reduce maintenance costs.

Transmission fluids and gear oils have also undergone changes over the years. Reduced viscosity and improved base stocks and additives have resulted in gains in fuel efficiency.

Recently, Eaton posted the results of some test work it undertook to demonstrate the fuel efficiency of its transmission and gear lubes. The results show that, in comparison with SAE 80W-90 mineral oil based lubricants, an SAE 50 synthetic transmission fluid and an SAE 75W-90 axle lubricant averaged about 1 percent better fuel economy. (See the test results in detail along with methodology at productssolutions/copyright/ testresults/index.htm.)

Now, at long last, we get to the engine oil story. I always like to save the best (or at least most interesting) for last. For this, I want to thank the industry experts who have been willing to share their views with me.

Since the late 1970s, SAE 15W-40 has been the engine lubricant of choice for heavy-duty vehicles (except for Detroit Diesel 2-cycle engines). SAE 15W-40 offers easier starting, less oil consumption and non-specific evidence of fuel economy improvements when compared to SAE 30 or 40 monogrades. According to the National Petrochemical and Refiners Association, 86 percent of the diesel engine oil sold today is SAE 15W-40.

Also since the late 70s, oil quality evolved from API CD to API CJ-4, with intermediate stops at all the other API C categories. In addition, engine manufacturers such as Caterpillar, Cummins, Detroit Diesel, Mack and Volvo all have inserted additional requirements over and above the API categories to protect their engines. Fuel quality has changed several times during the same period, from basically unlimited amounts of sulfur to the current 15 ppm maximum sulfur fuel known as ultra low sulfur diesel (ULSD).

Over the last 30 years, however, the fuel economy performance of heavy-duty engine oils has never been specified.

So, where are we going with heavy-duty engine lubricants and with fuel economy? Thats a two-part question, with a lot of activities going on globally. Lets begin with diesel oil specification-setting.

In the North American market, API CJ-4 is the most recent category. It has been in place for about two years, and was introduced to deal with the concerns that sulfated ash, phosphorus and sulfur (SAPS) in engine oils would adversely affect particulate traps, which were being used to meet 2007 emissions standards. However, it appears that many fleets have been able to successfully use CI-4 Plus engine oils (with higher SAPS) in vehicles with particulate filters and operate for over 500,000 miles before cleaning the filters.

The next big shift for heavy-duty lubes may come in 2014, when the final Tier IV non-road emissions standards come into play in the United States, effectively making on- and off-road emissions standards the same. In addition, thats the year the Euro 6 emissions standards take effect. Given similar hardware and standards, it seems likely that a global specification could be set then. That could set the stage for a proposed category – maybe PC-11?

However, a new wrinkle appeared at the last Diesel Engine Oil Advisory Panel meeting. Caterpillar reported seeing emulsions forming in CJ-4 oils under certain conditions. An industry task force has been formed to investigate and, depending on the outcome, we could soon see a call for a category upgrade – CJ-4 Plus or PC-11.

Now, for the fuel economy question: Japan has already introduced a heavy-duty fuel economy requirement based on mapping an engine on a dynamometer. It is in place and scheduled to get tougher in 2015. They are also considering an off-highway standard for construction and agricultural equipment.

In the United States, the Energy Independence and Security Act of 2007 requires DOT to study heavy-duty fuel economy and make recommendations within 18 months. Sometime in 2009, DOT will come back with recommendations. It seems probable, however, that any proposed standard would not be put into place before 2014 or 2015. Thats right in line with the next big move in engine oil standards, and could make PC-11 a bigger fish than we originally thought.

One concern many have is that DOT may set any heavy-duty fuel economy limits on a simple Corporate Average Fuel Economy model, as theyve done with passenger cars, rather than on a more realistic ton-mile/gallon measure. If that is the case, it could result in smaller trucks on the road, creating even more congestion than we currently see. For Europeans, attempts to rein in carbon emissions could drive fuel economy standards.

For the present, SAE 10W-30 engine oils are getting a lot of attention, and are now about 3 percent of the 350 million gallons of diesel engine oil sold each year in the United States. They are currently used in colder climates with great success. We know from passenger car applications that SAE 10W-30 gives better fuel economy than heavier SAE grades, and it seems reasonable to extrapolate that finding to the heavy-duty market.

Diesel engine builders are concerned, of course, about durability and will not take the leap to SAE 10W-30 without assurances that the fuel economy benefit more than offsets any wear/durability concerns. However, absent a fuel economy test for diesel engine oils, we can only safely assume that SAE 10W-30 engine oils might offer about 1 percent additional fuel economy. It could be more, it could be less.

Also, SAE 5W-40 products are in the marketplace now and are being used to good advantage. Because they are made using highly stable Group III and Group IV base stocks, there is a significant cost disadvantage for a fleet operator. There is not enough evidence of fuel economy benefit and/or drain interval extension to justify their use on that basis alone in the general market.

By now, I expect that many of you are busily calculating what lubes and all the other variables may mean in terms of total fuel economy benefits to the truck fleet.

The table above gives a pretty good rundown on all of the impacts discussed here and in last months column. Admittedly, not all of these improvements can be captured in their entirety, but there are a lot of gains that can be made in fuel economy.

From the lubricants side, there is not a great deal of impact – but every bit counts, just as in the passenger car market. With all of the other changes coming in the next five years, its safe to bet that well see a fuel economy requirement for heavy-duty trucks (and maybe one for their engine oils), new emissions standards and probably lower viscosity oils.

The OEMs will have their hands full! Your mileage may vary!

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