20 City MPG report by keeping rpm around 2k

I read something here and saw someone who had marked the range on their tack with GOOD and BAD ranges. I figured I'd give it a try. For the last 180 miles, I've tried very, very hard NOT to accelerate past 2000 rpm. I hit 3k a few times to get out of trouble, but for the most part, kept the needle below 2k.

I ran 180 miles and used 9 gallons on a straight, flat section of roadway here. Steady-state speeds ranged from 20 to 60 mph and there are a bazillion stoplights on this stretch of roadway. Truck has about 3600 miles on it and is a 2011 DC, LB 4x4 SR5 V6 AT with a Undercover tonneau cover. No lift kit, stock tires.

Thank you TW for a great tip!

 

I'm not surprised. On the highway, cruising at under 65, and with easy acceleration in what little in town driving I do, I gotten 23 mpg. However last Saturday I towed my trailer (5x10 w/ 24 inch sides) that was completely full of OSB with 2x6's on top of that, and OSB in the bed of the truck, pushing a headwind up I-35 out of Kansas City and I kept it at 60-65 mph and got 15.7 mpg.

 

If you pay attention, you can feel the sweetspot in the cams beginning around 1800 rpm, going up to about 2500 rpm. This is going to be your optimum efficiency range.

 

Thanks, I'll check that out!

 

Yes indeed, BUT driving a Prius will make a man drink lactose free decaf pumpkin spice lattes and I ain't going there.

 

Ahhh, I see. You drive a Prius!

 

Around town I drive like grandma. Even been flipped off a few times. The best I can do is 17 mpg.

 

You need to drive smart. I cruise at 65-70 and sometimes over that but I always average 22.5 mpg overall. Proper maintenance and driving smartly. That's what it's all about. You will never see me accelerating to a stop sign, that's for sure because it just a stupid thing to do. It wastes gas and brakes. I see it all the time. It's like people don't understand how to use the f'n gas pedal or know when not to use it. Every small decision I make has a reason behind it.

 

20 city is impossible for me.

too much traffic, too many hills.

besides..this is how that annoying hypermiling starts

 

"LESS REVS WINS". Ok, so, does that mean when I am downshifting a hill and the tach jumps up, even if I am not on the gas, is it still using gas to rev the engine, or is it now being run by the spinning of the axle, and no gas is being used? Is it more gas efficient to be driving faster, say 60 mph at 1500 RPM in top gear than driving 35 mph at 2100 in third? (THose numbers are just made up, but you get the idea) I've always wondered exactly how the engine works and when it uses gas.

 

I love this time of the year. Pumpkin Spice FTW.

Also, if I was worried about MPGs I would have bought a Prius. If I had to hypermile a truck I would drive the truck off a cliff.

 

I get 17.7 calculated only accelerating to 3k, Im under the theory of accelerating and getting to cruising speed earlier get me better mileage than slowly getting there, within reason tho.

And the 35mph at 2100 would be my choice to the above scenario, Id imagine at 60 wind resistance would come into play. I dont think it directly applies, but Id rather be in slightly higher rpm's and burn a little more gas, than lugging it and putting more wear and tear on the trans (more for a manual, than automatic)

 

I try to stay at 2000 rpms and I get about 20 mpg in my 4 banger.

 

A higher gear is always more efficient until a) engine load is enough to make it run richer than stoich, or b) the combination of high engine load and low rpm is enough to cause the slowing intake stream to stall and the vaporized fuel to condense.

There are two forces you're fighting for mpg in this case. There's engine friction (tends to increase at the square of rpm) and pumping losses (manifold vacuum). The faster-spinning engine will have to produce more manifold vacuum (throttle body less open) to not produce too much power and maintain speed; vacuum takes energy to maintain and is a constant drag force. This is why diesels win for highway mileage - no throttle body, always atmospheric (or above with turbo) manifold pressure.

Example: my six speed at 35 mph will spin about 2300 rpm in 3rd gear and about 1300 rpm in 6th gear. The ultra-gauge will read a maximum of 15 mpg on level ground in 3rd gear, but in 6th gear it will stay between 30 and 40 mpg (or as low as 25 to 35 when stone cold).

An automatic will downshift because it needs fluid pressure (and a certain rpm to drive the fluid pump) and the fact that torque against gears causes heat and a lower gear for the same wheel torque means less torque against on the active gears (and we all know what excessive heat does to automatics).

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Now for the easy way to think about it.

If you study the way an automatic works, you'll see that at low load it will always go to the highest gear it can, and under high load it will downshift. This is the model to follow when driving stick as well. Drive that rpm down when you don't need to go, and let it come up a bit when you do, to a point. The worst thing to do for fuel economy on a gas engine is lugging at high load for long periods of time - it's FAR better to just get it over with.

But since you're fighting that engine friction (goes up at the square of speed, remember) and fuel enrichment (makes more CO and NOx, get less energy from the gasoline that way), that's how you get the magic hypermiler mix - keep under 2000 rpm, accelerate at 80% load whenever acceleration happens, keep a steady foot to minimize tip-in (momentary enrichment whenever the pedal goes down), and use top gear whenever possible.

 

Dude, you're like a beautiful mind. Are you a professor, or something? I had to read it like 3 times. Thanks for that tho. Very insightful. Now even though I don't do this because it's not safe, but because the injectors shut off while coasting, is coasting downhill in neutral the same fuel efficiency as coasting down hill in gear, if you know at the bottom you will come to a stop and don't need more momentum? Obviously coasting down in gear will be better for your brakes, but we're not talking about that.

 

So are you saying that going up a hill lugging the engine in a taller gear with more pedal is more fuel efficient than goin up the same hill in a lower gear with less pedal and higher rpm? I would think the lower gear less pedal scenario would be more efficient, but after reading this thread I am a bit confused...

 

20 in city is possible for me, but its really hard. My all around avg is 21-23mpgs depending on where I'm going and how fast I need to be there.

 

Using a tachometer to stretch fuel economy is a good idea; but a better solution is use a vacuum gauge.

OK: When I was just a little kid, some cars came from the factory with a fuel economy gauge. I was just a vacuum gauge.

Before I lose you here; Google, Vacuum Gauge for fuel economy. OK, we are now on the same page.

Some Pontiacs in the late 1960's early 1970's were some of the cars that offered this option. Keep in mind, these cars were available with multiple carburetors (Pontiac, 3 deuces) and big cubic inch engines. These cars could suck a tank dry in a few hard burnouts. Even though gas was only 27 cents a gal. Other makes of cars had this option also.

Fast forward to the anemic engines of today: There is no reason why the approach you just read in, "Vacuum Gauge For fuel Economy" wouldn't work today.

"Nothing is new today, it has already been tried"

oldracer

 

Nah, not a professor. Maybe one day.

As for the second question, it depends on the hill and the speed. Anytime the injectors are off (that's called DFCO in hypermiler-speak: dynamic fuel cut-off) you're getting "free miles" so to speak. It's like the engine isn't even running.

As your question asks, if you know there's enough momentum to need to use the brakes to stop even if decelerating with DFCO the whole way down the hill, then absolutely that uses less fuel. The entire distance in question will use zero gas until the fuel starts flowing again at 10-15 mph or so. If it's done in neutral, the engine will be burning fuel to keep itself spinning instead of using up the truck's kinetic energy.

If it's a long and shallow hill, and the DFCO will bleed off too much speed too quickly to use the entire grade, then the next best choice is starting DFCO later on and focusing the choice of neutral vs in-gear on the segment before that. During that downhill time before DFCO, going down in neutral can save a marginal amount of fuel because then it's comparing time at in-gear speed versus idle speed, and over 45 mph idle speed fuel consumption will win every time.

Then there's the hardcore hypermiler's way - engine-off coast the whole daggum thing. Dangerous for the inexperienced to be sure.

Personally, I don't like coasting in neutral much with an automatic because it creates a situation where parts moving at high speed are lubricated with fluid pumped out at low pressure (that pump is on the engine side of the tranny); I've heard rumors of isolated cases of transmissions damaged from lack of lubrication, although that depends on the transmission (flat-towable vs not) and honestly I can't confirm that rumor. Some hypermilers run engine-off coast all the time on their flat-towable automatics, which is a more extreme example, but I don't believe the Tacoma falls into that category.

Just remember, if you start decelerating with the injectors off, if you touch the gas pedal even a little tiny bit, they'll turn back on and will STAY on. Pain in the butt Toyota logic.

Again it depends on engine load. A steep hill in top gear at 25 mph isn't too smart because load will go straight to 100% and efficiency will go down the toilet. My personal rule is from 1100 to 1300 rpm keep throttle at or below "just cracked open" and from 1300 to 1500 rpm below 70%. Any more than that really lugs the engine. If it goes too high, downshift. Burning condensed fuel is a great way to foul spark plugs... my first Honda taught me that. Not only that but oil pressure isn't so great at low engine speeds. Don't need to be banging the rods around a dry crank.

Look up a brake specific fuel consumption map for a better visual of this. A typical engine has highest efficiency around 2000 rpm at about 80-85% load; at lower speeds the best load % tends to goes down, hence my personal load rules previously specified. If you're spinning up a hill in low gear, efficiency will suffer, but the transmission will be cooler (this is why this situation would correctly apply when towing; vehicle longevity outweighs the need for good mileage).

On my six speed I'll do moderate hills in 6th down to 40 mph, in 5th down to 30 mph, and lower gears slower than that. Actually, I don't think there's any local instances of needing to use anything but 6th gear over 40 mph unless I want to scoot down the road or tow a trailer.

I bet you're alluding to a bicycle where you "spin it" to climb a hill. That's easier for muscles because high muscle exertion makes lactic acid too fast. A gas engine is backwards - it gets the most energy out of gasoline when it's working fairly hard.

 

I put on a lot of miles in my Civic with a vacuum gauge. It's a heck of a lot better than nothing. 3" of vacuum was about 80% load on that car.

There was the time when I had a manifold fire and it read +5psi until I killed the engine but that's another story.

As for my wall of text, sorry about that. That is literally how I think when going down the road.