OBC mpg accuracey

[mortod]

I today calculated my mpg after filling up and made it to be 33mpg, whereas the OBC over the same period averaged 42.3mpg. I assumed the difference was US gallons vs imperial, but if you think about it a US gallon is smaller which would give a lower mpg figure on the OBC if that was the case (have I got it the right way round?).

Has anyone else compares the OBC mpg to calculated? Is it just very innacurate?

Also, I managed to get 73ltrs into what is meant to be a 68ltr tank. How can that be?

Its a 2004 V70 D5 in the UK.

[T-5ones]

They are known to be very optimistic. I think it is calculated by flow rate as it cant really be measured exactly. Someone who knows what they are talking about will correct me. Mine claims 50 mpg ave. Its nearer mid 40's when calculated by the tank load. (01 P2 D5 V70)

[stainesy]

i was wondering about mpg as my 850 T5-R seems to say my mpg is normaly between 14mpg and 18mpg. thats crazey if im realy using that much fuel. does anybody no the normal mpg for an 850 T5-R?
sorry to piggy back you post

[Silverfox]

Not really the answer you are looking for but comparing the MPH shown on a SAT nav against the speedo in the car you will get a disparity - the cars speedo being enthusiastically high. As to filling the car I think the only thing we can guarentee is that a measure litre of petrol from a pump won't be a litre. Although it has to comply with weights and measures there has to be a tolerence band and it is interesting to note that you can get more litres in your tank when filling from certain places. With your 2 inaccurate pieces of information and the tolerance you get on the flowmeter measureing the fuel the figures we get are likely to be flawed. I have noticed if you 'chip' the engine and I'm talking about a sensible 10% chip the MPG rises noticeably. If you go this way don't forget to inform your insurer.

[mortod]

I think it must be the OBC that is wildly off. I was filling from my own 25ltr jerry can, so there is some room for error, though I did calibrate it by weighing 1ltr of water into a container, and then using that to calibrate the jerry. I'm using home brewed biodiesel, BTW, which is why I want to measure mpg as biodiesel is slightly less efficient than dino.

[LesRED850R]

i was wondering about mpg as my 850 T5-R seems to say my mpg is normaly between 14mpg and 18mpg. thats crazey if im realy using that much fuel. does anybody no the normal mpg for an 850 T5-R?
sorry to piggy back you post

Stainesy,Stainesy,Stainesy,.....If you are new to the power of the VOLVO TURBO you will be revelling in the smooth torque and boost spike revellation of the 5 cylinder TURBO and of course will pay the $$$$$ at the fuel bowser..Now a seasoned 850R driver like myself has been known to get [ you convert cause i cant be ######] 9.3 litres/100,kilometres. That is city and freeway and at worst when putting the "BOOT" in about 16.00/100klm. So if you have been enjoying your Volvo Turbo as you should be , you will pay a bit!! AND AINT IT WORTH IT !!!? So dont worry,its all fun!

[LesRED850R]

I think it must be the OBC that is wildly off. I was filling from my own 25ltr jerry can, so there is some room for error, though I did calibrate it by weighing 1ltr of water into a container, and then using that to calibrate the jerry. I'm using home brewed biodiesel, BTW, which is why I want to measure mpg as biodiesel is slightly less efficient than dino.

When the previous post spoke of "chip" he meant ECU not CHIP FAT to power your biodiesel car. Having built biodiesel plants run on CHIPS FAT/ Mc Downarlds left overs i must say that they are really run on CANOLA crop oil that in Australia means it is sent from Canada by big oil burning boats and it surely takes up food growing space where it was produced.... AND i lost a brand new $400 welding helmet into the CRUD that is left from the process,,its got yellow blobs and green mass and smells like.....you have to be there..... PEOPLE! IT IS NOT A VIABLE ALTERNATIVE.FOOD SOURCE WILL LOOOSE OUT ! GO LPG. Les m.

[rs_andy]

Assuming your are calculating it correctly yourself (ie filling up - running off most of the tank then filling up again and dividing litres used by 4.5 then mileage covered by the trip metre) then I would have thought there must be a problem with the meter that measures the flow of fuel as the obc and the speedo will both use the same signal to calculate how far you've travelled...

Checked mine only last week and it was right on the button.

True that the speedos are overoptimistic on the speed a lot of the time but that shouldn't affect the mpg calculation.

[LesRED850R]

[QUOTE=rs_andy;165561]Assuming your are calculating it correctly yourself (ie filling up - running off most of the tank then filling up again and dividing litres used by 4.5 then mileage covered by the trip metre) then I would have thought there must be a problem with the meter that measures the flow of fuel as the obc and the speedo will both use the same signal to calculate how far you've travelled..
RESPONSE FROM LESM> Oh i should just be quiet sometimes as people just dont listen........

[mortod]

Biodiesel from waste oil *is* viable. But biodiesel from new oil does indeed contribute to food shortages.

[LesRED850R]

Biodiesel from waste oil *is* viable. But biodiesel from new oil does indeed contribute to food shortages.

When people cant afford petrol they drive less.When they pay more for fresh food they cannot afford any other consumer product and that includes fish and chips...the biofuel idea and the government subsidies have to be stopped.And dont get me started about hybrid cars....who pays for disposing of the batteries when they die after 4 years?

[mortod]

I agree, and the Government announcement this week supports that - we should not be encouraging the growing of crops for biofuels. But the small scales production from waste oils is good for the environment. And 2nd generation biofuels (ie produced from oil from algae ponds) will also be good for the environment without the negative impact on foods; Government should be subsidising research into and ultimately production of that type of fuel. I'm not convinced by hybrid cars, and LPG is of course still a fossil fuel (plus for me it did not work out a cost effective conversion when you take into account its reduced mpg).

Anyway - way off topic. Has anyone else here compared calculated and obc mpg? a difference of 10, or 25% does seem a little extreme!

[LesRED850R]

[QUOTE=mortod;165618]I agree, and the Government announcement this week supports that - we should not be encouraging the growing of crops for biofuels. But the small scales production from waste oils is good for the environment. And 2nd generation biofuels (ie produced from oil from algae ponds) <Funny you mention the algae as when i was building the biodiesel plant the main aim was the very thing. They have the rights for the Asia Pacific for it and are doing interesting stuff as i am sure the European license crowd are too.Could make dirty coal power clean.......And as to the MPG readings,if you are worried about the fuel you should get out of a performance car....Where i live they all drive 4 door VXR monaro [equivalent ] between 185kw[97 model] and 307kw[current model] and they dont stopdriving in this fuel cost environment .Indeed,my mate has a Ford XR 8 ute with a 280kw V8/6 speed manual. and always will drive a V8 and says the people who drive small cars are saving all the fuel for him to use.......

[itguy]

My p2 V70 T5 computer is accurate to 0.5mpg either way.

I wonder if it's a ME7 vs 4.3 issue? - i.e. ME7 can calculate more accuratly?

[rs_andy]

[QUOTE=
RESPONSE FROM LESM> Oh i should just be quiet sometimes as people just dont listen........[/QUOTE]

why? did I miss something?

[cornclose]

The way I've always done it with all cars I've had is this :-

1. Fill up the car, from (almost) empty to 'full' (use the back-presure cutoff), and before you drive off from the filling station reset your trip odometer.
2. Drive, and next time you need fuel, fill up to 'full' (use the back-presure cutoff) again. Now, the amount of fuel you've just put in represents the amount of fuel you've used since the last refill to 'full'.
3. Using the amount of fuel from step 2 (in litres) and the mileage from your odometer at this time (the mileage since last refill) you have two pretty accurate figures from which you can calculate your mpg figure.

Remeber, 1 gallon is 4.54609 litres so use this accurate figure and don't round down.

Remeber also that the more times you repeat this process, keeping a tab on how many miles you've driven in total and how much fuel you've used, the more accurate your calculations will become. Keep hold of the fuel receipts as they will tell you the number of litres you're putting in.

Using the above method I get pretty much bang on figures when compared to my car's average, not just on the V70 but other cars I've had too. My Audi A6 was the same and so is my wife's VW Golf.

Finally, bear in mind that the car's average is a relatively long term average which is an integration of distance travelled against fuel used (exactly as used in the method described above) so calculating your average over one tankfull of fuel is not going to match what you see on your car's readout. However, if you start the above method and at the same time reset your car's average figure you should find that both mpg figures stay pretty damn close!

[CONDYBOY]

How do you brew bio diesel? is it safe in commonrail? Only I remember a prog stating that it's okay in older cars but not good for commonrail and something else about it clogging fuel filters faster than my auntie Maud goes through drawers after a dose of laxatives!