A Eureka Moment on MPG...

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Cornishman
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A Eureka Moment on MPG...

Post by Cornishman » Wed Mar 17, 2021 8:39 pm

Five days into ownership, one of the things I have been disappointed with is the displayed MPG... As a bit of a nerd I usually cross check the trip against brim to brim/ mileage gone calculation.

So the displayed figure was 34.6 mpg... After 330 miles I dispensed 35.42 litres to the "same" full point as when I topped the tank after leaving the dealer. That equates (330 /35.42/0.22) to 41.55 MPG. Car settings are on Imperial...

I had a similar experience on a motorcycle, where the trip calculated consumption in miles per US Gallon, so I got used to "updating" the readout in my head - multiply by 1.2

Lo & behold, when I multiply 34.6 by 1.2 that comes out 41.55... i.e almost exactly the same as my brim-2-brim calculation! I need to check in the car (OnLine says it's Imperial) to be sure, but I'm convinced!
Larry

NE Essex
21 XC40 R-Design B4 Thunder Grey, Climate Pack, Smartphone Integration, Towbar

Hugh Sername
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Re: A Eureka Moment on MPG...

Post by Hugh Sername » Thu Mar 18, 2021 9:27 am

How are you calculating brim to brim when you can't see the level. The spout goes through two flaps. Surely you aren't relying on the auto pump cutoff to determine it's full. This would be very unreliable.

If you have degrees C on the screen then your car is set to imperial. Degrees F then you are US gallons.
Last edited by Hugh Sername on Thu Mar 18, 2021 9:48 am, edited 1 time in total.

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m@rk
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Re: A Eureka Moment on MPG...

Post by m@rk » Thu Mar 18, 2021 9:33 am

Hugh Sername wrote:
Thu Mar 18, 2021 9:27 am
How are you calculating brim to brim when you can't see the level. The spout goes through two flaps. Surely you aren't relying on the auto pump cutoff to determine its full. This would be very unreliable.
Over time it would average itself out to be negligible.

I use a free tool called FUELLY for measuring fuel economy (see the banner in my signature) that I have used for years and years and for well over 1 million miles which is really useful at giving you real world stats (not just what the car thinks it has done). If you want to take the time to measure your economy, it's a great free tool
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Hugh Sername
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Re: A Eureka Moment on MPG...

Post by Hugh Sername » Thu Mar 18, 2021 9:47 am

m@rk wrote:
Thu Mar 18, 2021 9:33 am
Hugh Sername wrote:
Thu Mar 18, 2021 9:27 am
How are you calculating brim to brim when you can't see the level. The spout goes through two flaps. Surely you aren't relying on the auto pump cutoff to determine its full. This would be very unreliable.
Over time it would average itself out to be negligible.

I use a free tool called FUELLY for measuring fuel economy (see the banner in my signature) that I have used for years and years and for well over 1 million miles which is really useful at giving you real world stats (not just what the car thinks it has done). If you want to take the time to measure your economy, it's a great free tool
How about over 5 days of ownership and a single fill ?

Felindre
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Re: A Eureka Moment on MPG...

Post by Felindre » Thu Mar 18, 2021 9:57 am

Hugh Sername wrote:
Thu Mar 18, 2021 9:47 am
m@rk wrote:
Thu Mar 18, 2021 9:33 am
Hugh Sername wrote:
Thu Mar 18, 2021 9:27 am
How are you calculating brim to brim when you can't see the level. The spout goes through two flaps. Surely you aren't relying on the auto pump cutoff to determine its full. This would be very unreliable.
Over time it would average itself out to be negligible.

I use a free tool called FUELLY for measuring fuel economy (see the banner in my signature) that I have used for years and years and for well over 1 million miles which is really useful at giving you real world stats (not just what the car thinks it has done). If you want to take the time to measure your economy, it's a great free tool
How about over 5 days of ownership and a single fill ?
I think this is getting confusing, as cornishman wrote the original poster, but m@rk replied about fuelly.

I don't think the system is giving US readings, i just think they're low as the engine is tight. I've had this on all my from new cars over the last 10 years, and i expect the XC to improve over the next thousand or so miles.
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Hugh Sername
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Re: A Eureka Moment on MPG...

Post by Hugh Sername » Thu Mar 18, 2021 10:37 am

Felindre wrote:
Thu Mar 18, 2021 9:57 am
Hugh Sername wrote:
Thu Mar 18, 2021 9:47 am
m@rk wrote:
Thu Mar 18, 2021 9:33 am


Over time it would average itself out to be negligible.

I use a free tool called FUELLY for measuring fuel economy (see the banner in my signature) that I have used for years and years and for well over 1 million miles which is really useful at giving you real world stats (not just what the car thinks it has done). If you want to take the time to measure your economy, it's a great free tool
How about over 5 days of ownership and a single fill ?
I think this is getting confusing, as cornishman wrote the original poster, but m@rk replied about fuelly.

I don't think the system is giving US readings, i just think they're low as the engine is tight. I've had this on all my from new cars over the last 10 years, and i expect the XC to improve over the next thousand or so miles.
I have a T4, admittedly not as economical, on paper, as a B4. I've had it for over 2 years. I'm a careful, steady driver more interested in fuel economy than out and out performance.

Over the 2 years I've averaged 32mpg. And have achieved, on a few long motorway runs, a Max if 40 to 42mpg.

34 at first fill is very good, I wouldn't expect much more than 42 at the very best.

Regarding the monitoring, when I first started driving in the mid 70s cars had carburettors and you could see the level of petrol in the filling spout.

I can't understand in these days of highly accurate injection systems, that measure and record the smallest drop of fuel, and the inability to see the level in the filler tube, why you would rely on a brim-to-brim monitoring system rather than rely on the accurate feedback from the displays on the car itself.

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Cornishman
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Re: A Eureka Moment on MPG...

Post by Cornishman » Thu Mar 18, 2021 11:01 am

Hugh Sername wrote:
Thu Mar 18, 2021 10:37 am
I can't understand in these days of highly accurate injection systems, that measure and record the smallest drop of fuel, and the inability to see the level in the filler tube, why you would rely on a brim-to-brim monitoring system rather than rely on the accurate feedback from the displays on the car itself.
Unfortunately, the way that trip computers work the average out they DON'T give you an accurate answer. Because they're doing a continual update of the number it effectively becomes an "average of averages", which any statistician will tell you isn't a valid calculation. If it's accurate can you tell me why my average on the display (having reset at first top up) showed 34.6 but when I use the calculator it's 41.55? As for "seeing the fuel level", I filled the tank until the pump clicked twice on both occasions...

I have a very old Physics degree and the training that says "check your measuring equipment" still holds good for me. Yes I may be a bit anal about MPG, but otherwise how do you know the trip is accurate?
Larry

NE Essex
21 XC40 R-Design B4 Thunder Grey, Climate Pack, Smartphone Integration, Towbar

Hugh Sername
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Re: A Eureka Moment on MPG...

Post by Hugh Sername » Thu Mar 18, 2021 11:32 am

Average of averages. That's like saying a circle is really a straight line because each tangent is a straight line. You have to start somewhere!

You could, forgive the pun, keep going in circles arguing the various points in the system.

I'd much rather rely on a system that's actually based on what the car's systems are telling me, and driving the supply of fuel to the engine.

What does pump clicked twice mean? Does a Shell pump click at a different point to an Esso? Do you also measure the distance travelled using a calibrated metre rule, or do you use the car's odometer? And what about the diameter of the tyres and the temperature?

It's a never ending cycle of measurement! I'm happy with letting the car do its work and you're happy with how you measure; so we're both happy 🙂.


To reiterate I think your 32mpg is good and expected. I drive like I'm driving Miss Daisy and the most I get on a long run is 42. Haven't done much mileage, blame the Covid in that, only about 8,000 in two years. Used to do about 20K/annum when I worked.
Last edited by Hugh Sername on Thu Mar 18, 2021 11:52 am, edited 3 times in total.

Chris John
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Re: A Eureka Moment on MPG...

Post by Chris John » Thu Mar 18, 2021 11:50 am

I really don’t get those that are obsessed with fuel consumption

Go out and drive the car and enjoy it. You fretting about fuel consumption isn’t going to make the fuel consumption better.
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Hugh Sername
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Re: A Eureka Moment on MPG...

Post by Hugh Sername » Thu Mar 18, 2021 11:56 am

I tend to ignore what others think of what I'm interested in. They're my interests after all.

I suspect you may have some interests that I haven't the smallest interest in 🙂.

To be honest I'm doing so few miles that I've started to put Shell V in and am flooring it.

Just need to get a furry dice and a back to front baseball cap.

And don't get me started with litter dropping.

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