My gas mileage doesn't make sense to me.

[fuzzybabybunny]

2000 Toyota Echo Manual 108K miles.

11.9 gallon tank, highest mileage I've gotten is a little over 500 miles on one tank (I've also ran out of gas recently trying to get this a second time ). Highest miles per gallon is 45mpg.

Doing 70mph on the highway in 5th @ 3K RPM for the entire tank is about 42mpg.

Doing 30-40mph through twisting mountain roads, up and down, usually in 2nd and 3rd gear most of the time for the control and the power to make it up the hills with my little 108hp engine: 45mpg

Doing 60mph on local 55 mph roads in fifth for the entire tank: 45mpg

My engine seems to be most efficient at 2K RPM. 50mph in 5th is 2K RPM, so I think I might be able to push my mpg to maybe something like 46 or 47 if I did an entire tank at 50mph in 5th.

The mountain part doesn't make much sense to me. I'm going slower, revving higher, usually driving harder (because I like the curves ), and climbing up hills, but also coasting down some in gear.

 

[spidey07]

easy - you're not using a drop of fuel when you let off the throttle.

 

[Gibson486]

If I was getting 4x mpg.....I would not question anything about gas mileage in my car .

 

[fuzzybabybunny]

Originally posted by: spidey07
easy - you're not using a drop of fuel when you let off the throttle.

I know, but I'm also using MORE fuel during the climbs, and also by nature of the fact that overall I'm almost always revving high while doing so. I would think that this would somehow balance out with my coasting in gear.

 

[iamwiz82]

Originally posted by: fuzzybabybunny

Originally posted by: spidey07
easy - you're not using a drop of fuel when you let off the throttle.

I know, but I'm also using MORE fuel during the climbs, and also by nature of the fact that overall I'm almost always revving high while doing so. I would think that this would somehow balance out with my coasting in gear.

The only true way to test is to measure you gas mileage going through the mountains both ways and then averaging everything. Perhaps the route you took was more downhill than up and you just didn't notice?

 

[nanogirL]

Originally posted by: iamwiz82

Originally posted by: fuzzybabybunny

Originally posted by: spidey07
easy - you're not using a drop of fuel when you let off the throttle.

I know, but I'm also using MORE fuel during the climbs, and also by nature of the fact that overall I'm almost always revving high while doing so. I would think that this would somehow balance out with my coasting in gear.

The only true way to test is to measure you gas mileage going through the mountains both ways and then averaging everything. Perhaps the route you took was more downhill than up and you just didn't notice?

thats right, you cant ever get an exact mpg. only an average. everything can become a factor from the road to wind conditions to the air levels in your tires.......
just be happy that it hits over 40 mpg.

 

[fuzzybabybunny]

Originally posted by: nanogirL

Originally posted by: iamwiz82

Originally posted by: fuzzybabybunny

Originally posted by: spidey07
easy - you're not using a drop of fuel when you let off the throttle.

I know, but I'm also using MORE fuel during the climbs, and also by nature of the fact that overall I'm almost always revving high while doing so. I would think that this would somehow balance out with my coasting in gear.

The only true way to test is to measure you gas mileage going through the mountains both ways and then averaging everything. Perhaps the route you took was more downhill than up and you just didn't notice?

thats right, you cant ever get an exact mpg. only an average. everything can become a factor from the road to wind conditions to the air levels in your tires.......
just be happy that it hits over 40 mpg.

Well, the thing is that these numbers are gathered through many different drives and over a span of about 4 years. EVERY time I drive through the mountains (which has been about 5 times), the mileage has been from 44-45mpg. In fact, it has never gone lower than a high 43mpg. I've done a ton of driving doing exactly 70mph on the highway, and it has never hit 43mpg. 41.5-42.5mpg is the concrete range, with no outliers outside this range.

So yes, each single tank of gas can have lots of external factors, but considering the length of time (4 years) and the number of drives I've done, and still gotten extremely close mpg numbers for each type of terrain, these external factors should just average out as well.

 

[zig3695]

Originally posted by: fuzzybabybunny
The mountain part doesn't make much sense to me. I'm going slower, revving higher, usually driving harder (because I like the curves ), and climbing up hills, but also coasting down some in gear.

exactly, youre going half the speed as you would on the highway. anything over 55mph and youre exponentially killing gas mileage. plus, your car is light as hell, so the hills dont matter as much.

 

[jagec]

Originally posted by: zig3695

Originally posted by: fuzzybabybunny
The mountain part doesn't make much sense to me. I'm going slower, revving higher, usually driving harder (because I like the curves ), and climbing up hills, but also coasting down some in gear.

exactly, youre going half the speed as you would on the highway. anything over 55mph and youre exponentially killing gas mileage. plus, your car is light as hell, so the hills dont matter as much.

Yeah, plus the engine is probably running at a more efficient point when hill-climbing. So while it uses more fuel than it would on flat ground at 70, the downhills more than make up for it.

The best mileage I've gotten on my MR2 (on one full tank) was during a club run...redlining every gear, speeds between 30-70 on a really curvy, empty road. ~32 MPG. City driving really kills that.

 

[fbrdphreak]

Your engine may be most efficient at 2K RPM, but if you're doing 2K RPM in 5th you are probably having to use a fair amount of throttle to maintain speed or accelerate.

It is a hard balance to guesstimate, but depending on how big your gear spread is you might get better gas mileage in 4th gear @ 55mph because you'd use a lot less throttle.

Just a thought

 

[jagec]

Originally posted by: fbrdphreak
Your engine may be most efficient at 2K RPM, but if you're doing 2K RPM in 5th you are probably having to use a fair amount of throttle to maintain speed or accelerate.

It is a hard balance to guesstimate, but depending on how big your gear spread is you might get better gas mileage in 4th gear @ 55mph because you'd use a lot less throttle.

Just a thought

Actually, a more open throttle butterfly is MORE efficient. Assuming you're not lugging the engine, your best mileage will be in the highest gear that still generates enough power to keep the car moving, because that way (1)The butterfly will be more open and (2)It'll be at a lower RPM.

 

[Eli]

Originally posted by: jagec

Originally posted by: fbrdphreak
Your engine may be most efficient at 2K RPM, but if you're doing 2K RPM in 5th you are probably having to use a fair amount of throttle to maintain speed or accelerate.

It is a hard balance to guesstimate, but depending on how big your gear spread is you might get better gas mileage in 4th gear @ 55mph because you'd use a lot less throttle.

Just a thought

Actually, a more open throttle butterfly is MORE efficient. Assuming you're not lugging the engine, your best mileage will be in the highest gear that still generates enough power to keep the car moving, because that way (1)The butterfly will be more open and (2)It'll be at a lower RPM.

I think people tend to overstate the efficiency losses from the throttle butterfly. Yes, it's more efficient.. but its more or less negligible compared to other things.

He is exactly right. In my Insight, I get the best gas milage by NOT keeping the RPM as low as possible.

This often happens when I'm trying to accelerate in 5th at like, 40MPH.

Time is the biggest factor. It takes too long to gain speed, and during that time I may only be at 35MPG.

However, in 4th.. the RPMs are higher, but I can keep the fuel consumption display at say, 40MPG and I'm also accelerating more quickly.

I can get 60MPG in 3rd @ 60MPH @ over 3,000RPM if I can get lean burn to kick in...

I'll try and explain better later, gotta hit the road.

 

[dug777]

Originally posted by: jagec

Originally posted by: fbrdphreak
Your engine may be most efficient at 2K RPM, but if you're doing 2K RPM in 5th you are probably having to use a fair amount of throttle to maintain speed or accelerate.

It is a hard balance to guesstimate, but depending on how big your gear spread is you might get better gas mileage in 4th gear @ 55mph because you'd use a lot less throttle.

Just a thought

Actually, a more open throttle butterfly is MORE efficient. Assuming you're not lugging the engine, your best mileage will be in the highest gear that still generates enough power to keep the car moving, because that way (1)The butterfly will be more open and (2)It'll be at a lower RPM.

I would have thought that WOT (aren't I cool? ) would use considerably more fuel than ticking over with barely any throttle, at the same rpm.

WOT () when maintaining constant speed would imply significant loading (towing and/or a hill), and everytime I've towed my fuel consumption has increased, despite needing more throttle to maintain the same rpm, without 'lugging', which by your argument should reduce my fuel consumption...

Similarly, everytime I've driven a a car with a digital fuel consumption readout up a hill, fuel consumption displayed has increased as I've opened the throttle maintaining rpm, compared to just cruising along the level with barely any throttle...

WOT...

 

[zig3695]

in general almost all cars are most efficient in their normal gear @30mph give or take 5. anything below you still save gas but its not much different, anything higher- especially above 55- get much worse solely because of air drag and gravity. the faster you go the more those two pull you back, and the way cars are geared (65mph highway) they almost always obtain peak efficiency around 30mph.

butterfly open means engine has most vacuum.. more vacuum is always good yet i tend to like to keep my engine clean by running it above 2500rpm normally....

 

[jagec]

Originally posted by: dug777

I would have thought that WOT (aren't I cool? ) would use considerably more fuel than ticking over with barely any throttle, at the same rpm.

WOT () when maintaining constant speed would imply significant loading (towing and/or a hill), and everytime I've towed my fuel consumption has increased, despite needing more throttle to maintain the same rpm, without 'lugging', which by your argument should reduce my fuel consumption...

Similarly, everytime I've driven a a car with a digital fuel consumption readout up a hill, fuel consumption displayed has increased as I've opened the throttle maintaining rpm, compared to just cruising along the level with barely any throttle...

WOT...

That's because in any REAL situation, you're only at WOT when you're demanding lots of power from your engine...and power equals gasoline. Yes, the engine is more efficient when at WOT compared to partial throttle at the same RPM, but efficiency is not measured by MPG but by fuel consumption per unit power.

So if one car is cruising along at partial throttle, and an identical car next to it is cruising at WOT while towing a trailer which causes it to require exactly twice as much power to remain at a steady speed, the second car will get lower gas mileage than the first, but not half the gas mileage...which means that the second car is a more efficient situation.

In short:
partial throttle at 2000 RPM, let's say 20 hp output, sips 2 gallons per hour
WOT at 2000 RPM, let's say 50hp output, sips 4 gallons per hour.

The first situation consumes less fuel, but the second situation is more efficient.

 

[dug777]

Originally posted by: jagec

Originally posted by: dug777

I would have thought that WOT (aren't I cool? ) would use considerably more fuel than ticking over with barely any throttle, at the same rpm.

WOT () when maintaining constant speed would imply significant loading (towing and/or a hill), and everytime I've towed my fuel consumption has increased, despite needing more throttle to maintain the same rpm, without 'lugging', which by your argument should reduce my fuel consumption...

Similarly, everytime I've driven a a car with a digital fuel consumption readout up a hill, fuel consumption displayed has increased as I've opened the throttle maintaining rpm, compared to just cruising along the level with barely any throttle...

WOT...

That's because in any REAL situation, you're only at WOT when you're demanding lots of power from your engine...and power equals gasoline. Yes, the engine is more efficient when at WOT compared to partial throttle at the same RPM, but efficiency is not measured by MPG but by fuel consumption per unit power.

So if one car is cruising along at partial throttle, and an identical car next to it is cruising at WOT while towing a trailer which causes it to require exactly twice as much power to remain at a steady speed, the second car will get lower gas mileage than the first, but not half the gas mileage...which means that the second car is a more efficient situation.

In short:
partial throttle at 2000 RPM, let's say 20 hp output, sips 2 gallons per hour
WOT at 2000 RPM, let's say 50hp output, sips 4 gallons per hour.

The first situation consumes less fuel, but the second situation is more efficient.

:thumbsup:

I gets ya

 

[mooseracing]

Originally posted by: spidey07
easy - you're not using a drop of fuel when you let off the throttle.

oh god, not this again

 

[maluckey]

It's easier than everyone is making it.

Mechanical advantage of lower (numerically higher) gearing, coupled with running the car near it's torques peak, combined with light weight and not much aerodynamic drag at the reduced speed = good mileage.

My old Neon with a 3.94 final drive and .81 fifth gear, got 38-40 MPG highway, and 34-36 city. The reason that it was relatively indifferent to situation was that it weighed almost nothing, had short gears, and ran most of the time in the sweet spot.

 

[PeeluckyDuckee]

Weight and drag at higher speed. Even though you're climbing a hill and revving higher, you may be operating near the efficiency of the engine where the power/torque is. Plus the fact that you're actually driving slower up and down the hill, with turns and everything, where the hills may have blocked off some air turbulence, makes it an overall better MPG situation than cruising at 70mpg on a straightaway.

 

[Ronstang]

You also get better mileage at altitude if your car is fuel injected. You have less power at altitude also since there is less air, and thus less gasoline, being ingested every cycle.