With fuel prices likely to stay high through the growing season, farmers should consider cutting their diesel bills by trying the often-overlooked practice of “gearing up and throttling back.”
“I think there are a lot of people who could take advantage of it,” said Robert Grisso, a University of Nebraska mechanical engineer.
“All you’re really doing is matching the load up with where the engine’s going to work more efficiently.”
The basic concept is simple: when full engine power isn’t needed, a farmer can reduce his engine speed by shifting to a higher gear.
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The advantage is that an engine running with fewer revolutions per minute under a moderate load will use substantially less fuel than an engine running at full throttle with the same ground speed.
In tests last year, a four-wheel drive Case-IH 338 p.t.o. horsepower tractor pulling a 50 percent load at half power used 24 percent less fuel than it did running at full throttle.
It also had better fuel efficiency doing the same work as a much smaller John Deere 188 p.t.o. tractor, proving that a large tractor can be just as fuel efficient as a smaller mechanical front-wheel drive machine doing the same work, Grisso said.
The large tractor burned more than three litres less per hour.
Gearing up and throttling down can only be used for operations in which 70 percent or less of a tractor’s power is needed.
P.t.o. operations are also difficult or impossible with this method because lowering the rpms of the engine also reduces the p.t.o. speed.
It is also important not to lug the engine. A sure sign of lugging is excessive black exhaust smoke. The smoke reveals large amounts of unburned diesel.
Lugging occurs when rpms are too low to produce enough torque to perform the work. This can damage the engine by placing too much pressure on bearing surfaces and also damage the transmission, clutch and final drive.
A good way to check whether the engine is running right or lugging is to run at the rate you’ve selected, then suddenly open the throttle. If the tractor easily picks up speed there is no problem.
But if the engine has trouble speeding up, you’re probably lugging it. The answer is to shift to a lower gear.
Many farmers don’t gear up and throttle down, even though the method has been suggested occasionally by people like Grisso.
Whenever fuel prices rise, it becomes more popular, he said, because fuel becomes a bigger part of the variable costs.
But some farmers have also avoided gearing up and throttling back because they were once told it was a dangerous practice.
Many equipment manufacturers used to warn producers not to run the engine below full operating power or they would lose their warranty.
This was particularly true of gasoline engines, which generally need to run at high rpms to produce the necessary torque.
But now that virtually all tractor engines use diesel, and diesel tractor engines have been re-engineered to provide higher torque at lower rpms, most manufacturers say the practice is safe and efficient.
Doug May of the Prairie Agricultural Machinery Institute in Portage La Prairie, Man., agrees.
“There is substantial reason to think there are savings,” said May.
