| June 12, 2007 |
Many equipment managers have come to rely on oil sampling to give them a more accurate indicator of when to change oil and service a machine. But oil sampling, although quick and inexpensive, is a diagnostic tool more than a scheduling tool.
To get a more precise indicator of how hard a machine is working, a handful of equipment managers across the country have started using diesel fuel consumption rates as the standard by which they establish service intervals. The logic is as simple as the method is precise. The more fuel a machine burns, the harder it is working and the faster the oil and the engine’s internal components are wearing out.
Heavy loads accelerate wear
“The severity of the load on an engine is directly proportional to the fuel burned,” says David Taber, technical coordinator for ConocoPhillips. “And you’re not just working the engine, you’re driving the hydraulics, fuel injectors, transmissions and other areas just as hard.”
One of the early pioneers of fuel-based maintenance, Dale Warner, corporate equipment manager for Maryland-based C.J. Langenfelder & Son, says he has been using the method since the early ’80s.
“We had been going with the manufacturers’ recommendations of 250-hour service intervals, but we weren’t burning as much fuel as we should have been,” Warner says. “I got some literature that said you should burn 70 gallons of fuel for every quart of oil of sump capacity between service intervals.”
Fuel consumption rates vary on any machine depending on the application. But in general Warner found he could extend service intervals on some machines to as much as 500 hours while others needed service intervals as short as 175 hours. Scrapers, he says, were particularly big fuel consumers, while most of his haul trucks used less fuel than expected.
Warner has continued to use fuel consumption as the primary factor in scheduling almost all his equipment maintenance and has conducted seminars for the Association of Equipment Management Professionals on his methods. (For more on the AEMP, see page 30).
The cost savings Warner documents for machines with low fuel consumption rates are impressive. For a 10-gallon crankcase, an oil change with labor costs about $600. If that machine would normally see 40 oil changes over its life, and you can cut that number to 28, the savings comes out to roughly $7,200 per machine.
Scheduling other fluid changes
In addition to engine oil changes, Warner developed a multiplier based on fuel consumption to schedule other fluid changes and component service. His transmissions, final drives and differentials all get serviced every four oil changes. “The one component where we change the fluid every time we change the engine oil is the pump drive on excavators,” he says. “The gearbox that drives the pumps only holds two to three gallons of fluid, so it will get a lot of wear quick. Another thing we change every time is the final drives on LGP dozers. It seems like they stir up so much dirt that they get a lot of high-silica dirt in them.”
Warner also uses his fuel consumption rates to determine the lifecycles of some engines. His rule of thumb for overhauls is 100 gallons of fuel burned times the engine’s size in cubic inches.
Measuring fuel accurately
Equipment managers with large fleets and their own fuel trucks have an easier time tracking fuel consumption than those with smaller fleets and multiple sources of fuel. Bill Fenkner, eastern fleet advisor, Pennsylvania Department of Transportation, oversees a fleet spread over 67 counties and collecting and analyzing fuel consumption data is just part of the everyday procedure.
Fenkner’s fueling data is matched to specific machines and entered into a mainframe computer daily by each of the 67 garage clerks. Operators who get fuel outside the DOT system use a fuel card with pin numbers that are keyed to specific vehicles. The card company exports that information into the DOT’s computer system.
Warner’s crews are also asked to record fuel consumption daily. “A lot of those we do manually,” he says. “The fuel guy writes down the meter reading. We are gathering some by electronic data, but not very much because we’ve had problems with that.” On jobs in remote locations, Warner asks fuel vendors to send him machine- specific information.
Pilot study matches fuel to hours
Brett Burgess, the maintenance planner at Kokosing Construction in Fredricktown, Ohio, doesn’t use fuel-based scheduling on a regular basis, mostly because of the difficulty of recording accurate fuel data. But five years ago Burgess, along with Jack Butler, the company’s equipment manager at the time, performed a fuel useage study to find out which machines gobbled up the fuel and which were stingy. Burgess found he could extend the service intervals on his excavators from 250 to 300 hours. “We’re saving a bit of money without compromising the lifetime of the machine,” he says. Butler adds that fuel consumption can also be used as a management tool by comparing fuel use to machine history or the manufacturer’s expected fuel consumption.
Burgess says he has considered using Palm Pilots and other types of technology to get better fuel recording, but for now the company is still looking for an easy and cost-effective way to collect the data.
The backup plan
While fuel consumption rates may be the most accurate way to gauge engine service intervals, they are not the only interval to be used in all cases.
Pennsylvania’s DOT fleet, used extensively in wintertime snow removal, has to be ready to rip at a moment’s notice and work around the clock for days on end. So calendar-based service scheduling can take precedence over fuel consumption totals.
“Even if a piece of equipment doesn’t meet the fuel consumption window, it still comes in for preventive maintenance on either a 30-, 60-, or 90-day schedule, says Fenkner. “The usage may be down and we may not change the oil, but we want to keep an eye on it so it’s at its peak of readiness when it’s time to use it. We give the equipment managers a range as far as gallons of fuel burned. Most of them don’t go to the extreme end of the window unless we have a major snowstorm.”
Warner also builds some safeguards into his scheduling. “First we set it by gallons of fuel. Secondly by hours and third by date. So we will definitely see the machine within one of those three windows,” he says.
Verify with oil analysis
Oil analysis is frequently used to monitor engine health and to tell whether it’s OK to extend drain intervals. For fuel-based maintenance intervals, oil analysis is even more important.
“If the engine is running harder, there are more demands on the lubricants. You may have higher oxidation rates and you may want to look at using a higher quality engine oil or shorten your drain interval,” Taber says.
Sulfur can also become a big issue in severe-duty engines. The amount of sulfur in off-road diesel can vary from as little as 500 parts per million to as much as 5,000 ppm. “The oil’s total base number is directly affected by the sulfur content of the fuel,” Taber says, “and sulfur is a big contributor to the acids in the oil.” Oil analysis that measures total base number can catch this before it becomes a problem.
Making the commitment
With more than 10 years of data to back him up, Warner, who manages a fleet of more than 900 pieces of off-road equipment, is a true believer in the merits of fuel-based service intervals. Still, he admits, switching from an old maintenance system to something new can be intimidating.
“I know when people start looking at 400- and 500-hour service intervals, they start getting scared,” Warner says. “If the owners think there’s a chance you might blow up an engine, the easy way is just to stick with the recommended service intervals. But I’ve done it long enough that management supports what I do.”
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