For years now, farmers have been hearing the throttle-down-gear-up phrase. It’s how you can save a few dollars on daily tractor fuel consumption rates, simply by changing the way you operate the machine. With PTO jobs, however, you couldn’t do that. Powered implements need to run at their rated speed in order to work properly, and that means running the tractor’s engine at rated PTO speed all the time during those operations, whether you need full power or not.
Now, some manufacturers are giving you that throttle-down-gear-up capability for jobs using powered implements. The way to do that is to include an economy PTO feature on their new models. You may see it referred to as a 750 RPM PTO on some spec sheets. When the PTO shaft is running at 540 in the economy mode, the engine speed is significantly slower than when in normal operation. That greatly reduces fuel consumption.
Whether it’s a standard feature or an option depends on the brand, but if you’re buying a tractor that will see a lot of PTO work, selecting one that has the economy feature may significantly reduce operating costs over the life of the tractor.
Put it to the test
To see exactly how much lower daily operating costs could be, let’s take a look at a test analysis done by the Nebraska Tractor Test Lab (NTTL). The following numbers are based on fuel consumption data taken from a John Deere 5101E Limited tractor (NTTL test 1905A) tested on a dyno at their facility. During the test, it was operated in both the normal and economy PTO modes while the fuel consumption and horsepower output were measured.
Both test runs were made with the tractor putting out exactly the same effort, about 65 horsepower. “We wanted to do that to show comparable data,” says Dave Morgan, assistant director at the NTTL.
While on the dyno, the 5101E consumed 14.87 litres of fuel per hour using the economy PTO mode. In the next test, with the same measured output, the lab operated the tractor in the normal PTO mode. That meant throttling the engine up from 1715 RPM to 2400 to keep the standard PTO shaft speed.
Fuel consumption climbed quite a bit — to 17.74 litres per hour, an increase of 2.87 l/hr. Assuming a cost of about 95 cents per litre for diesel, that’s an extra fuel expense of $2.72 per hour. Work your tractor for eight hours in the economy mode instead of the regular PTO setting and you’ve saved $21.76 over the course of the day. That’s enough to take your wife out to dinner — if she’ll settle for a burger at A&W.
The 5101E’s maximum PTO horsepower at rated engine speed was about 83, so it’s clear the tractor can put out a significant portion of that, even with the engine running relatively slowly; that’s because most of today’s diesel engines offer pretty good torque in the low RPM range. So, the economy PTO mode can be used for a pretty wide variety of jobs.
I looked through the Nebraska test results for economy PTO performance in other tractor brands, but couldn’t find any. “Not all manufacturers choose to test that,” says Morgan. He couldn’t think of any tests other than on John Deere tractors that included that data. But it’s a pretty good bet tractors from other brands that include the economy PTO feature offer descent fuel consumption advantages, too.
The other benefit is the lower noise level inside the cab when the engine is running slower. The NTTL measured the decibel level inside the 5101E’s cab at 82.5. That is on the high side of what many premium tractor cabs offer today. Throttling the engine down would make quite a difference to the operator’s comfort level, which would make you feel even better about saving over $20 per day on fuel.
Every little bit of cost saving helps, right? †