40.9 mpg is the best i could achieve

[MrJames]

So I filled the tank back up, it wasn't completely empty but 58.3L went in and I'd driven 630 miles by this point which based on actual fuel usage it returned 49.13MPG I'm pretty impressed by this for such an old car!

[stuart bowes]

that is pretty good even for a diesel from what I've read, I assume you do gentle acceleration and not driving fast?

that is a long distance though to be fair.. what's your urban like?

[MrJames]

Well before the trip it was sat at 40mpg average, that's a mix of short drives to work ( about 8 miles each way ) and medium drives ( about 35 miles each way, mix of A road and B roads with small out in the sticks singletrack roads so crawling speeds )

Now it's sat at 43.4MPG

[stuart bowes]

I do mine the other way around which is arguably less accurate.. every week I let the needle get to start of the red (not as far as the light coming on), put fuel in, then log the number of litres on the receipt against mileage.

so i'm relying on gauging by eye where the needle is, but it's close enough to be reasonably accurate

if you're doing it by brimming the tank then noting mileage when you brim it again, theoretically that's more accurate because you can't over fill it can you

splitting hairs though really - it would only make a difference of about 0.5-1,mpg at worst.. and my 'errors' would average themselves out anyway because I have a weekly average and a cumulative average on my spreadsheet

then again if you don't need a full tank because you're only doing local trips, you're carrying around all that extra weight of fuel which is less economical. saying this if my last journey was anything to go by, these Volvo's don't seem to even notice being fully loaded! I literally couldn't squeeze any more in and it made not one even slightly noticeable difference to handling or braking

[ASt85]

Originally Posted by stuart bowes

I have a weekly average and a cumulative average on my spreadsheet

My current urban mpg tank top up to tank top up is currently 26.9mpg with an average speed of 12.7mph : considering it is a 2.3 T5 geartronic I'm reasonably pleased as the longest journey in the last 18 months was the round trip to to my preferred MOT garage a few months ago, Mick's MOTs in Rochester, some 5 miles away.

The owner, Mo, collected the car and returned it the same day - honest MOT, honest advice and always willing to provide help when needed.

[Georgeandkira]

Excerpted from above: "...if you don't need a full tank because you're only doing local trips, you're carrying around all that extra weight of fuel which is less economical. "

True, but I like having a full tank so there's less air space for atmospheric moisture. The purge cycles of the EVAP system draw in air from the outside.

My long trips are less than 1/2 tank away. I let it go down during the outing but make sure it's full when I park it once home. This goes double when rain is predicted.

Hey, if my aversion to moisture in a fuel system is a throwback to steel tanks (which my '07 has) or is insignificant due to the alcohol in our petrol (alcohol attaches to water molecules and passes it with the petrol) then the joke's on me.

[stuart bowes]

well it's an interesting different perspective I suppose.. I've not heard that before

I suppose there's not really a lot in it, the whole 'less economical' thing is theoretically correct but how much real word difference it makes? I dunno. would be suprised if it was more than 1mpg. probably the worst things are whatever causes more drag, like rolling resistance from low tyre pressures, air resistance from things on the roof rack, windows open etc.

if you fill the tank up all the time, maybe just go up 1 or 2 psi on the wheels and it counteracts the difference?

total guesswork of course

[Georgeandkira]

I'd no sooner adjust my tire pressure to fuel load than for passengers of differing weights.

[Bashy]

Originally Posted by Georgeandkira

Excerpted from above: "...if you don't need a full tank because you're only doing local trips, you're carrying around all that extra weight of fuel which is less economical. "

True, but I like having a full tank so there's less air space for atmospheric moisture. The purge cycles of the EVAP system draw in air from the outside.

My long trips are less than 1/2 tank away. I let it go down during the outing but make sure it's full when I park it once home. This goes double when rain is predicted.

Hey, if my aversion to moisture in a fuel system is a throwback to steel tanks (which my '07 has) or is insignificant due to the alcohol in our petrol (alcohol attaches to water molecules and passes it with the petrol) then the joke's on me.

Not so sure about atmospheric moisture (humidity) myself, more likely to be condensation due to temp differences.

I cannot remember the last time i filled a full tank, damn, that was a straight up lie, i filled 3 jerry cans end of last autumn, a kind of tanks i suppose, then i brimmed th mower tank a few times but then i spose we are talking vehicle tanks so back to those, nope, still cannot remember the last time i filled to the top, there was my old K4 GSXR 1000, i used to brim that, that was back in 2004, i am trying to figure out if i went up to see my mum before she passed before or after then, ah hold on, i took my 1st ever dog up to see her, that was 2012 as he was about 6-8 months, so there ya have it, last time was 2012. and in all my years of driving, never had an issue with water and fuel, i rarely fill to the top, i work on the weight idea myself.

When i used to have my T5's, i could tell when i had someone else in the car with me, well, namely my mate that was about 14st, the power was lower, 100% straight up, i could tell, and if the power is lower, it means its using more fuel too, so over time that extra 1/4 to 1/2 a tank is deffo gonna cost you and theres no reason to do so re moisture. If its just to keep a full tank in case of, thats different in spose, depends how often that "case of" happens...

Well, thats me rambling on a bit, carry on.....

[stuart bowes]

Originally Posted by Georgeandkira

I'd no sooner adjust my tire pressure to fuel load than for passengers of differing weights.

Well it'd be worth doing it once, if you're always in possession of a full tank. I didn't mean let air out as you use fuel and top them back up when you fill it again