Disappointing fuel economy plus fuel tank size

forgotmyname

skiddlydiddly wrote: »

Well if you can drive at say 3k rpm in 4th gear doing 40 mph but can just as easily drive at 2k rpm in 6th gear doing 40mph without labouring the engine and using the same throttle, which do you think is going to use the most fuel?

Just because peak torque is at a certain point, it doesn't mean you actually need to be using that many revs to maintain your speed without wearing the engine.

Depends if the engine has enough power and torque to maintain 40mph at 2000rpm.

thor

smitchy73 wrote: »

Thor,
As others have pointed out, you need to fill your tank, then do your journey taking a note of the mileage, either by a simple start and finish and the difference, or reset your trip computer if you're car has one. Then when you're ready fill you're tank again to the brim, and work out how many gallons you have filled with, divided by the miles and that will give you you're mpg.
My car until I started working out myself was telling me about 51/52 mpg, but when I work it out it is actually 48mpg, still not too bad for a 2.0l diesel.

I looked at my tank this morning and realised through sheer coincidence that I have effectively done what everyone has been suggesting. Before refuelling and journey start my tank was on the 1/4 mark and at the journey's end (395 miles later) the needle is back on that exact same mark.
I put petrol in twice. £45 @1.19 litre and £15 @1.29litre(guess which was service station and which was supermarket forecourt:mad:)
So by my reckoning that works out at 395/[(45/1.19x4.5) + 15/1.29x4.5)]
= 36mpg. Everyone agree?
so still disappointing.

Inactive

But the exact mark where your fuel gauge shows a given amount can vary, even parking on a slight slope can alter the actual reading.

So I would still suggest to you that your method is flawed.

keith1950

Hi, this is a large car with a 2 litre petrol engine, I know two people with same car ( different years ) that get average of 34 mpg, this rises to 36 mpg on long motorway runs but can drop to 32 mpg when purely around town motoring. I don't think you can expect any better than this ..... and yes , the only way to check mpg is to fill tank, run the car till nearly empty and fill again.

angeltreats

Inactive wrote: »

But the exact mark where your fuel gauge shows a given amount can vary, even parking on a slight slope can alter the actual reading.

So I would still suggest to you that your method is flawed.

This is true. I do the exact same journey every week and fill up after exactly the same number of miles. Sometimes the needle is in the red and sometimes it's just above it. Filling up right to the top is the only way to do it.

BTW I check my fuel consumption every time I fill up, just to keep an eye on it. I drive 80 miles a day, mostly national speed limit dual carriageway with some motorway and a few miles of very steep hills. I get around 41-42 mpg although I do tend to do 80 odd most of the way and a bit more on the motorway if I'm in a hurry - I expect a bashing from the anti-speeding brigade . I know when I was just travelling around closer to home and seldom going over 50 odd, I was getting closer to 50 mpg.

cyclonebri1

thor wrote: »

I looked at my tank this morning and realised through sheer coincidence that I have effectively done what everyone has been suggesting. Before refuelling and journey start my tank was on the 1/4 mark and at the journey's end (395 miles later) the needle is back on that exact same mark.
I put petrol in twice. £45 @1.19 litre and £15 @1.29litre(guess which was service station and which was supermarket forecourt:mad:)
So by my reckoning that works out at 395/[(45/1.19x4.5) + 15/1.29x4.5)]
= 36mpg. Everyone agree?
so still disappointing.

Thor everyone has told you to go by the tank not the gauges or the manufacturers figures, yet you still stick with your highly innacurate method, why???.

thor

cyclonebri1 wrote: »

Thor everyone has told you to go by the tank not the gauges or the manufacturers figures, yet you still stick with your highly innacurate method, why???.

because it has occurred to me that filling from empty to brim still requires you to use the gauge for the empty tank state. How does this differ from filling from 1/4 mark and ending up back at the 1/4 mark? Admittedly it was sheer fortune that the needle ended up where it began but this surely must be just as valid as using the empty tank marker.

LandyAndy

thor wrote: »

because it has occurred to me that filling from empty to brim still requires you to use the gauge for the empty tank state. How does this differ from filling from 1/4 mark and ending up back at the 1/4 mark? Admittedly it was sheer fortune that the needle ended up where it began but this surely must be just as valid as using the empty tank marker.

As I said in my first post, you don't grasp what is required.

Imagine you have no fuel guage.

There are only two states that you can be sure of, full and empty.

We are going to work with full.

Fill the tank to, say, the second click of the pump. You don't need to know how much you've put in.

Zero the trip counter. Drive for some miles, say about 300.

Now fill the tank in the same way again and note the amount of fuel put in.

You now know exactly how much fuel you have used to cover the 300 or so miles and you haven't needed a fuel guage or to know how big the tank is.

Inactive

Far too simple..

( and accurate as well )...:)

cyclonebri1

thor wrote: »

because it has occurred to me that filling from empty to brim still requires you to use the gauge for the empty tank state. How does this differ from filling from 1/4 mark and ending up back at the 1/4 mark? Admittedly it was sheer fortune that the needle ended up where it began but this surely must be just as valid as using the empty tank marker.

You do not need to start with an empty tank, but the lower it is, the more accurate the result. Note the mileage, brim it, drive, when nearly empty do the same again and use the fuel used to brim it a second time to work out for used for your driven mileage:eek:, I've just realised you might just be winding us all up.

Forget the Goddam guage, :T