All other things being equal,lets say you are going 45mph and you are going down a perfectly flat road, wind speed is zero, can you get better mpg in a lower gear with higher RPM?
I would think not because there would br more internal friction to overcome, though on a friends vehicle it sometimes seems if you manually drop a gear the instant MPG display will read the same or 1mpg better when dropped into lower gear.
Its Its really hard to determine the variables such as wind speed and direction, grade ect… so I know my observation is far from scientific or in a controlled environment.
The vehicle in question is a 2016 Chevy Colorado, 2wd, 4cyl. I believe it has an electric cooling fan.
In general, no, because you’ll likely be at a smaller throttle opening in a lower gear, increasing pumping losses. Same reason low (numerically) final drive ratios improve fuel economy.
I’ve always heard that you get the best fuel economy when you’re at the lowest speed you can maintain in the highest gear. If that’s true, then your scenario would be worse.
That’s my perception, also. Of course, with a stick shift, one has to make sure that he’s not lugging the engine, but with that proviso, the lowest speed in the highest gear should yield the best mpgs.
Two factors, load such as lugging, and rpm. Rpm takes more fuel unless the engine is being lugged.
I rented a 4.cyl manual vauxhall
and that sucker would be hitting 3000 rpm on the highway in high gear. Liter after liter of gas. Mine run at 2000 at 70 with respectable mileage.
The instant MPG toy is probably vacuum based so there are times when it is meaningless. The 85 Cadillac would read 70 MPG when going downhill.
My other story involves an 87 Mazda truck. I drove uphill to two peaks on South Vandenberg AFB. I was in second gear a lot and I expected a bad MPG reading at the next fill-up. Not a bit of difference. Everything is different around Lompoc Ca. Now; about the weather…
My 2011 Outback reads 99 mpg when coasting downhill. When I have to resume applying the gas pedal, it reads anywhere from 24-26 mpg, depending on my previous driving behavior.
The hills on South Vadenberg Space Force Base seem pretty small, even if you drive down to the ocean off the plateau. I didn’t go much last SLC-6 though, and not inland.
I believe the computer is reading the injector pulses for the mpg calculation. When I had on board diagnostics, I could watch the changes in the injector pulses just for entertainment on a long drive.
I’ve done this test on my Lincoln a number of times. The last being a 1500 miles road trip to CO in my Lincoln Mark where I kept meticulous records to prove my point.
The Mark gets roughly 2 MPG better at 70 as compared to 55 and that was verified a number of times by the dash readout along with the fill/miles traveled method. There was at most a .1 MPG discrepancy between the methods.
I attribute the improved mileage at higher speed to 2 things.
One is that at 55 the Mark’s engine is lugging. It does not even begin to breathe until between 70 and 75. The other is that at 55 and below the car’s stance is elevated. Over 55 the air ride automatically lowers the car by one inch to improve aerodynamics.
The Mark will also get 99 MPG coasting downhill. Too bad that mode would not stick…
Same with the only bike I ever bought new; a BMW R/100. At 55 MPH it was kind of a dog and got 35 at best. Over 70 MPH the engine would start to breathe a bit and mileage was mid 40s.
Tranquillion peak is about 2,000 ft. Looking down seems higher than looking up. It’s a slow climb at low speeds. The first three gears are low in the pickup, the next two are too high. Nice trip.
With automatic transmissions and torque converters this can happen. 3rd with the torque converter locked can get better fuel economy than 4th unlocked. Sometimes a lot, like 15 MPG in 3rd and 11 MPG in 4th under heavy load. It could apply with the torque converter unlocked in all gears too.
With a manual I don’t think there’s a situation where a lower gear has better fuel economy. But maybe there is an exception with some extreme near full throttle situations or very low RPM. 4th gear is direct but over drive 5th gear adds a little more friction. Only one of the gears will be direct drive in a manual transmission. Things have also changed with newer engines having variable valve timing. At very low engine RPM the combustion may begin to cool off before the piston travels all the way down, leading to more heat being lost in to the engine instead of being used to put out power. It’s a good question!