I'm saving on my fuel bill_ if you have a car which tells you your mpg as you drive

Pew_Pew_Pew_Lasers!

Not all speedometers overread, and most by nowhere near 10%.

AdrianHi

saveallmymoney wrote: »

Car trip computers are normally fairly accurate, except that the speed over reads by 10% for the uk market. So subtract about 10% off your MPG and thats what it is.

See this has been one of those discussion topics I've looked in on over the last couple of years on a car enthusiast forum and the reality is, even for exact same model and age of car you can get a variance of anywhere in the range +/-15% on an OBC result compared to manual brim to brim calculation over the same period - i.e. you reset the OBC mpg at the same tiem you fill up. The difference between calculated result and OBC result is not even that consistent.

saveallmymoney

AdrianHi wrote: »

The difference between calculated result and OBC result is not even that consistent.

Clearly some cars will.suffer partially blocked injectors or other faults which disturb the way the fuel use is measured. Otherwise injector pulse timing should be really accurate.

Its been very consistent on all the cars i've had with a trip computer, on those cars where the computer has a "fuel used" this has always been within half a litre over a full tank. The mileage however nearly always agrees with the speedo, which is 5-10% over. (10% on my Mondeo at the moment, varies with tyre wear and inflation).

AdrianHi

saveallmymoney wrote: »

Clearly some cars will.suffer partially blocked injectors or other faults which disturb the way the fuel use is measured. Otherwise injector pulse timing should be really accurate.

... some in the sample set I'm talking about, including my own car, have had this behaviour since brand new and at least a couple of us (again including me) use additives which help keep the injectors clean.

Peter De Nayer a former technical researcher for the AA did quite a bit of research in this area, official vs. real world fuel consumption.
"Peter makes the interesting statement that car trip computers can seldom be relied on" (not the same as never relied on).
http://www.green-car-guide.com/news/official-mpg-v-real-life-mpg.htm
Some interesting results here about how fuel consumption increases with speed, not so much for smaller less powerful cars. Also larger engined cars get closer to "official" figures meaning in the real world the gap between an apparently "economical" car and a less efficient car is not as big as it it seems on paper.

tomstickland

You can even save fuel without a display. Basic tips are:

-back off the accelerator early if you need to slow down for a feature ahead
-anticipate what traffic is doing so as to avoid braking and then acceleration
-don't pansy about with very slow acceleration - use up to half throttle; a short burst of moderate acceleration is preferable to a long, slow acceleration
-practice the art of smooth, flowing driving. Bin the jerky boomerang style
-back off the power when travelling up hills
-reduce cruising speeds

using the above I managed a 20% improvement over "don't care about mpg" driving.

thescouselander

Pew_Pew_Pew_Lasers! wrote: »

Not all speedometers overread, and most by nowhere near 10%.

Yeah, my speedo reads pretty much exactly the same as the GPS indication on my satnav which should be fairly accurate.

lancasterchelsea

when I posted some time ago I was getting about 950 miles on a tankful ... redeye audi a4 tdi
I had some engine mods done about 5 years ago. It was retuned for economy
also the valve that recycles the waste exhust gases was blocked off.
I was driving 200 miles on motorway every day M6/M62 and my speed averaged about 55 mph using cruise control
I filled up brim to brim over about 3 months
Now the car is older (about 190,000 miles) and I am averaging about 65 mpg
If I am running about town/locally I get 60mpg

almillar

Please look in your mirror when you're doing these economy drives, and don't shake your fist when you're overtaken! I drive economically in traffic, but I don't want to be stuck behind you crawling away from the lights on the open road!

Norman_Castle

My current car is a 1.9 non turbo diesel. As the timing belt is 16 years old, the clutch screeches under load and the driveshafts are worn and getting worse, I am slow away from the lights. I just go through the gears at low revs. At low speed cars are normally in my boot, but while changing through third, fourth and into fifth the gap increases as the car behind is still in the lower gears. Any cars that overtake never seem to get far ahead unless they are keen to speed. I have never understood why some drivers lurch away from the lights in the dash to 20mph.

almillar

Hopefully your timing belt will snap soon and you'll be out of our way. Maintain your car properly, no timing belt should have to last 16 years. Hope you've got a recovery service!