I guess I don't have a decent car. I find my fuel consumption increases
quite a bit when driving a 80 rather than 65. Throw in headwinds and
mountains and there is more variability. It's a confirmation of why the
gas gauge is dropping rapidly. I usually fuel at about 300 miles but if
the consumption is up I plan an earlier stop. In the western US there
aren't filling stations behind every bush.
Guess my truck isn't "decent" either - and nor was my Taurus. The new
Kia has the built-in trip computer.
I have a scanguage in the truck.
I have a totalizer I was going to put in the plane - measures gallons
or liters per hour - not per mile - as well as total amount consumed
but is no good on a fuel injected engine with bypass.
No OBD2 on the fiat 600D so can't use Scanguage on it. I may hook up
the totalizer to monitor furl since the guage is notoriously
in-accurate -- - -
Trade it in on a Fiat 500... like the New Beetle and the Mini-Cooper
Fiat seems to have taken what was a cheap little car and turned it into
an expensive little car. My Yaris is closer to the original idea of the
Cooper than the nostalgia version.
I did some measurements in my Golf TDI auto. Anything up to 55mph was equally efficient, after that I lost 5mpg per 10mph. And of course trying to keep at a constant speed without braking and accelerating a lot helps massively. The odd result that contradicts what most people say is that it was just as efficient driving slowly (eg 20mph in a built up area - as long as it was a continuous 20 and not lots of junctions to stop at - might have been the auto gearbox that helped with that, modern autos have a torque convertor so it's always in the optimum gear, sometimes inbetween gears).
I don't understand why they don't make cars with a better range, just add a bigger tank! Even in the UK I find it irritating that I have to refuel quite often. When I had a car that ran on LPG it was very annoying as there were hardly any stations with it. Wait till we all have electric cars that only go just over 100 miles before needing a half hour charge, everybody's going to be sat around a lot, we'll need more cafes....
I just refuel every time I spot it down to a quarter full. Obviously if I was somewhere with a lack of fuelling stations, I'd fill up at half full.
Above that speed aero effects become more dominant.
People with manual typically choose a gear and stay there. An auto will
use lower revs until the driver presses the pedal. Internal friction of
an engine is about 3kW/1000rpm so if a driver chooses 2000rpm but the
auto chooses 1500rpm that's roughly a gallon over 20 hours.
I had a TD for a while. Driving on narrow, undulating West Country roads
could be more economical than on the flat, despite needing brakes and
sometimes more revs. An example of the benefit of pulse modulation (no
load/high load) and energy storage (potential energy, in this case).
What people are you referring to? Myself and most people I know will drive in the highest gear they can without the engine struggling. Perhaps if you're in a situation where you'd have to change every 10 seconds, you wouldn't bother and the auto would.
I don't believe you. An engine is less efficient if you place a higher demand on it.
Don't believe it if you don't want to. That is your nature.
That would create the impossible condition of having highest efficiency
with no demand at all. And a low gear would be better than a high gear.
Remember my mention of 3kW/1000rpm internal friction? If you ask for 1kW
out, the engine has to produce 4kW. Ask for 3kW and it only has to
Have a look at:-
Only lazy folk drive like that. I change up a gear whenever possible. Unless I need power, I keep the revs below 1500.
Everybody knows it's more economical to drive at a constant speed, and not to stress the engine. You're a cyclist, right? Which do you find easier, a nice steady even pace, or pedalling as hard as you can then freewheeling?
No, I never said there was no lower limit. I find the most economical revs is 1000-1500, which is what an auto does.
No, spinning the engine at 6000rpm is less economical.
This is in agreement with what I'm thinking, that you waste fuel per revs. So it's best to always run the engine at low revs. Your idea of it being more economical to drive on narrow, undulating West Country road doesn't make sense, that's going to require gear changing and revving all the time.
Not many people know what they are talking about. Also, what is stress
in this context?
Actually, I prefer to cover the boring bits then stop to look at the view.
Anyway, muscles are different to a mechanical engine. With stored energy
they can peak at about 1kW for a few seconds but can't replenish at more
than about 150W.
When cruising the average consumption is similar to instaneous consumption.
When changing speed or travelling over hilly roads, they are not
directly connected. Instantaneous consumption will fluctuate but it
doesn't mean that under periods of high consumption the efficiency must
If going along the flat requires 5kW and the consumption is 40mpg but
going uphill at the same speed requires 20kW, then anything above 10mpg
means the engine is more efficient. Irrespective of revs deployed. The
potential energy then drives the car downhill so the average is restored
or improved upon.
From experience I can tell you it's most economical to drive at a constant speed with low revs.
Using it harder.
I was talking about what uses the most energy.
Maybe so, but the same principal applies, using them nowhere near their limit is more efficient.
The simplest thing to consider is, does the engine run more efficiently when pushed hard or treated gently? Running an engine at quarter power all the time, or half power half of the time, which is best? I think you'll find quarter power all the time wins.
It's less economical because of the higher speed inside the engine.
I read what you wrote above, which presumably is the same as the links?
Prior to variable cam timing an engine had a fairly predictable
maximum torque RPM - and at that RPM the engine was most efficient at
converting fuel to horsepower. Maximim fuel economy was achieved at
that rpm in the highest gear that the engine could maintau that RPM
not considering aerodynamoc drag. On some efficiently designed cars
the efficiency advantage of the engine at that speed overcame the
aerodynamic drag penalty. Getting the gearing and the aerodynamics to
ballance out was a bit of a trick - Toyota goit it right a few times,
and not so good other times. The 1975 Celica GT 5 speed was an example
of getting it right. Better than 45MPG at 2800 RPM in 5th gear. At
55MPG you couldn't squease 25MPG out of it.
In 1976 they changed the gearing and the advantage went away.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.