I got 40 mpg from full tank of diesel, but first half I was seeing 62 mpg ? so confused, please hel

FastLife91

Torque Junkie
Points
57
Location
England
Car
Ford Focus mk2
My car is a 2006 focus 1.8 TDCI Sport, written mpg for it are urban 39.2 mpg to 64.2 mpg extra urban.
I often get 400 mostly urban miles.

I had full tank diesel, drove 180 miles on motorway and by calculating where the gauge was I had used £13 (litres) which was 62 mpg approx. However I then drove 50 miles urban at which point I was at half way on fuel (takes 22 litres from half to fill to brim). so I calculated again and did 230 miles using 22 litres and my mpg only showed as 44 mph.
By the time my low fuel light was on I had only drove 420 miles, which is only 20 miles more than I get at urban.
why , when I calculated my mpg after the 180 mpg motorway trip I was seeing 62 mpg, but once I calculated my mpg from full tank it fell to 42 mpg ?
I drove 60 mph all the way there and back and stayed in slow lane throughout
thanks
 
Was one way more downhill and the return trip uphill ;) :)

PS forgetting my manners so welcome to a great site with a bunch of helpful people.
 
Hello and welcome. It is quite common to get massive MPG reductions on the motorway, especially at speeds of around 60mph. I find that Vpower gives me better MPG than the standard diesel fuel.

On a full tank my car tells me I have 550 miles left. I only usually get around 470-500 in reality due to the urban driving that I do.

Trip computers are not that accurate really, the only real way to tell is to work it out yourself, which is why we created this page. https://www.torquecars.com/tools/uk-mpg-calculator.php
 
Hello and welcome. It is quite common to get massive MPG reductions on the motorway, especially at speeds of around 60mph. I find that Vpower gives me better MPG than the standard diesel fuel.

On a full tank my car tells me I have 550 miles left. I only usually get around 470-500 in reality due to the urban driving that I do.

Trip computers are not that accurate really, the only real way to tell is to work it out yourself, which is why we created this page. https://www.torquecars.com/tools/uk-mpg-calculator.php

The written mpg for my car, urban 39.2, extra urban 64.2, combined 52.3

I topped up £15 to fill tank to brim, drove the 180 motorway miles at 60 mph and saw the fuel gauge still higher than before putting in £15, estimated I used £13. had I put 13 litres in, it would have been full to brim again = 62 mpg.
I then drove a further 50 miles around town and fuel was half way, checked mpg on here and it showed 44 mpg, so from 50 it had dropped from 62 mpg to 44 mpg

I get 40 mpg around town so it looks like only 4 mpg more from motorway ??


if I refilled straight after 180 miles trip, I'd have got 62 mpg


I don't have a mpg on the tripmeter, I calculate my mpg on this website
 
Have you checked the usual stuff like tyre pressures, dragging brakes etc...

This is really strange. You should see consistent figures for similar types of driving and motorways should give much better fuel economy.

Also fuel gauges are not linear, half a tank on the fuel guage usually equates to around 1/3 of a tank left. The last half is usually shallower than the first half in most cars. Mine moves very slowly to half then seems to zip through the last half.
 
1
Have you checked the usual stuff like tyre pressures, dragging brakes etc...

This is really strange. You should see consistent figures for similar types of driving and motorways should give much better fuel economy.

Also fuel gauges are not linear, half a tank on the fuel guage usually equates to around 1/3 of a tank left. The last half is usually shallower than the first half in most cars. Mine moves very slowly to half then seems to zip through the last half.

Could it also be that the MAF wiring on my loom is damaged which is why the engine light is on, could this be a reason ?
 
Very probably yes. A bad MAF signal will upset all sorts of things.

** I am still slightly thrown by miles per gallon per tank.

OK got it now. You are surprised by the huge difference in one tank full of fuel. Sorry !! Do bear in mind that driving style and journey type will make the biggest differences of all to fuel economy.
 
Very probably yes. A bad MAF signal will upset all sorts of things.

** I am still slightly thrown by miles per gallon per tank.

OK got it now. You are surprised by the huge difference in one tank full of fuel. Sorry !! Do bear in mind that driving style and journey type will make the biggest differences of all to fuel economy.

No worries, glad you understand, I have a condition that makes trying to express myself very difficult and it gets me frustrated.

Yes, so the first quarter of my tank saw me get 180 miles from £13 (13 litres) which = 62 mpg. but then I drove 50 urban miles and reached half way point on fuel tank. it takes 22 litres ot refill from half way so this time I did 230 miles from 22 litres and shows my mpg fell to 44 just from driving 50 miles around town.
would this be right ?
 
No worries, glad you understand, I have a condition that makes trying to express myself very difficult and it gets me frustrated.

Yes, so the first quarter of my tank saw me get 180 miles from £13 (13 litres) which = 62 mpg. but then I drove 50 urban miles and reached half way point on fuel tank. it takes 22 litres ot refill from half way so this time I did 230 miles from 22 litres and shows my mpg fell to 44 just from driving 50 miles around town.
would this be right ?

Town driving is a lot heavier on fuel than steady state driving on main roads. Of course, as speeds increase you will see an increase in fuel usage, though driving style does make a big difference. If the town worn was particularly heavy traffic then this would seem reasonable. Bear in mind that if you are stationary with engine running you are averaging zero mpg. Diesels do a little better than petrols in this respect but the numbers are still not great.

With regard to the MAF wiring down mentioned, does your car show any warning lights on the dashboard?

As per explaining and expressing yourself, take your time and do ask for help if you need to clarify something, or need it clarified for you. This is a very friendly place, there's no bigotry or discrimination here. Hello & Welcome to Torque Cars btw.
 
Hi and welcome to TC forums.
Just a thought but filling to the brim you have extra fuel up the filler pipe which is not accounted for on the fuel gauge. I go about 80 miles before I even see the gauge move on my Golf and the range is always going up instead of down for first 100 miles of a full tank as computer thinks I'm using no fuel as tank sensor would be on full for all those miles. I get 600 miles out of a 60ltr tank and that's all I ever worry about TBH.
 
The OBC in mine seems to work on difference between fuel flow and return ie. completely independently of the tank gauge. It is possible to get some strange results by changing driving style halfway through a tank of fuel. Our OP though is going by tank gauge, which, like you say, not the most accurate way. The only true measure really is to fill it to the very top and then record mileage at each successive refill. Again to the very top. This, I think is called the brim-to-brim method. I never have the patience to do this..
 
Hi and welcome to TC forums.
Just a thought but filling to the brim you have extra fuel up the filler pipe which is not accounted for on the fuel gauge. I go about 80 miles before I even see the gauge move on my Golf and the range is always going up instead of down for first 100 miles of a full tank as computer thinks I'm using no fuel as tank sensor would be on full for all those miles. I get 600 miles out of a 60ltr tank and that's all I ever worry about TBH.

my previous car's, I could fill to the brim and the fuel needle would not move until about 70 miles of driving

on current car, drive around 5 miles and the fuel needle begins to move from full, could this be related ot damaged maf wiring ?
 
Town driving is a lot heavier on fuel than steady state driving on main roads. Of course, as speeds increase you will see an increase in fuel usage, though driving style does make a big difference. If the town worn was particularly heavy traffic then this would seem reasonable. Bear in mind that if you are stationary with engine running you are averaging zero mpg. Diesels do a little better than petrols in this respect but the numbers are still not great.

With regard to the MAF wiring down mentioned, does your car show any warning lights on the dashboard?

As per explaining and expressing yourself, take your time and do ask for help if you need to clarify something, or need it clarified for you. This is a very friendly place, there's no bigotry or discrimination here. Hello & Welcome to Torque Cars btw.
Hi
Yes, engine light on reading open range or open circuit regarding maf loom
 
Definitely you do need to do this.
Hi

I will do, I want to sort problem with slight water loss first, I will try bleeding it tomorrow as I am sure there is air trapped in there


quick question - The overflow pipe has some bubbles in it but no bubbles whatsoever in expansion tank, should this be a worry ?

ty
 
Obviously the complete removal of air is best but a few traces of bubbles won't hurt. I'd be more worried if there was air inside the block or head. This can, in exceptional cases, cause localised overheating, which can, in exceptional cases cause engine damage. I suspect that the coolant level would fluctuate widely if this was the situation here.
 
Obviously the complete removal of air is best but a few traces of bubbles won't hurt. I'd be more worried if there was air inside the block or head. This can, in exceptional cases, cause localised overheating, which can, in exceptional cases cause engine damage. I suspect that the coolant level would fluctuate widely if this was the situation here.

Hi

Yes, can't see any bubbles in expansion tank, only in coolant pipe.

Hopefully after bleeding it with cap off and hot air on will remove the air bubbles.

Coolant is not erratic, not rising too high, no bubbles in tank, just seems to be a slight drop in water every day or so
 

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