Fuel consumption

[Bert321]

I read on another forum that speedos reading high is due to UK laws.  There was quite a bit of info on it, but the general gist is that apparently it's illegal (in the UK) for a speedo to under-read, so the manufacturers build their tolerances into over-reading to keep their a$$es covered.

[Caldean]

That was my understanding  too... so setting cruise at 73mph is why I still end up overtaking all those drivers who think they're doing 70 when in fact they're only going at 67 mph....

[Catamong]

This is my first AT and so have nothing to compare it to but that said, I've been brought up to understand that an automatic will always use more fuel as a result of the full range of any gear being utilised whereas this is seldom the case with a manual box.

Yes it defiantly takes the revs higher before changing, unlike the manual, with the manual the gear change indicator often come on well before 2K revs.

IMO this is one reason why the auto uses more fuel, it takes much longer to get into 6 speed.
The 8 speed ZF used in the Bmw will often match the manual car with economy figures and emissions.

But a X1 costs a lot more to kit out to the sport standard.

I'm amazed at the Newbies on here who actually believe what the on board display is telling them, surely you guys know you're being hoodwinked, there have been so many posts on here to that effect..?

The only true way to calculate MPG is to record actual litres put into the tank against mileage covered, and, believe me, you will find a significant discrepancy between what the display tells you, and what you are getting in real life, fact.

Cat.

[xtrailman]

This is my first AT and so have nothing to compare it to but that said, I've been brought up to understand that an automatic will always use more fuel as a result of the full range of any gear being utilised whereas this is seldom the case with a manual box.

Yes it defiantly takes the revs higher before changing, unlike the manual, with the manual the gear change indicator often come on well before 2K revs.

IMO this is one reason why the auto uses more fuel, it takes much longer to get into 6 speed.
The 8 speed ZF used in the Bmw will often match the manual car with economy figures and emissions.

But a X1 costs a lot more to kit out to the sport standard.

I'm amazed at the Newbies on here who actually believe what the on board display is telling them, surely you guys know you're being hoodwinked, there have been so many posts on here to that effect..?

The only true way to calculate MPG is to record actual litres put into the tank against mileage covered, and, believe me, you will find a significant discrepancy between what the display tells you, and what you are getting in real life, fact.

Cat.

I amazed that you actually think brim to brim is accurate, it isn't.
As I have already posted my A4 was only around 1mpg high, which isn't really worth carrying out brim to brim checks.

Once I do establish the error for my car I won't be doing brim to brim refills very often if at all, it uses more fuel carrying more weight than required.

The only accurate way to establish a real mpg reading is to use calibrated instruments, only whatcar does that.

[Deeps]

Once I do establish the error for my car I won't be doing brim to brim refills very often if at all, it uses more fuel carrying more weight than required.

The only accurate way to establish a real mpg reading is to use calibrated instruments, only whatcar does that.

xtrailman is spot on with both statements and working on the assumption that most of us are not going to invest in calibrated instruments such as that used by whatcar then that only leaves the option of brim filling with the negative such as pointed out, or to get on and drive the thing and forget all about  consumption. I recall something that the salesman said to me upon purchasing my first ever BMW and enquiring as to servicing costs. He replied, quite firmly as it happens - "if you have to enquire as to serving costs then perhaps you shouldn't be considering a BMW car".

[Willpower]

I amazed that you actually think brim to brim is accurate, it isn't.

I disagree. Please explain why you think this method is inaccurate. Provided that you fill the filler pipe to the same level every time and do the correct mathematical calculation, the result is far more accurate than any mechanical or electrical component.

As I have already posted my A4 was only around 1mpg high, which isn't really worth carrying out brim to brim checks.

Then I suggest that either you were not filling to the same level, or your calculations were in error.
There have been innumerable postings on this forum and on the other Mazda forums which have all reported a difference of between 3 & 5 mpg positive difference when doing brim to brim against that reported by the vehicle. That could offer a difference of up to 50 miles on a full tank. Not an unsubstantial distance.
 

Once I do establish the error for my car I won't be doing brim to brim refills very often if at all, it uses more fuel carrying more weight than required.

Your last point may well hold some credence. But then it all depends on your circumstances.  The argument for a full tank can be supported by the requirement to always be able to travel. no matter where or how far, without having to worry if you have enough fuel to make it, or if there is a filling station open.

In my previous position ( before retirement) it was necessary for me to travel long distances in an emergency, any any time of day or night. Peoples lives depended on it.
I could go to bed and know that if I was called out at 3am there would be no delay due to having to refuel. 
So given individual circumstances, it could quite easily be more beneficial to drivers to always have at least half a tank available at all times. 

The only accurate way to establish a real mpg reading is to use calibrated instruments,

Agreed.  The trouble is that the instruments in your car and not just yours, but everybodys, are not calibrated sufficiently and regularly to be deemed accurate.   
According to the premise behind ISO 9001  the following is true.

The interval between re-calibration is determined by a number of factors:

• manufacturer recommendations
• operating environment
• accuracy requirements
• how long the instrument historically stays ‘true’

When did you last check the accuracy of your gauges ?

As in many other discussions over this matter, there will always be two sides to an argument. And it will all depend upon whether the people reading it will be concerned enough to actually make a considered opinion.  There are those who blindly believe that the gauge is always right because Mazda says so. And those who think for themselves and wish to have a more informed outlook on where their money is going, which will enable them to make concerted efforts to lessening the impact on their wallets.

[Catamong]

This is my first AT and so have nothing to compare it to but that said, I've been brought up to understand that an automatic will always use more fuel as a result of the full range of any gear being utilised whereas this is seldom the case with a manual box.

Yes it defiantly takes the revs higher before changing, unlike the manual, with the manual the gear change indicator often come on well before 2K revs.

IMO this is one reason why the auto uses more fuel, it takes much longer to get into 6 speed.
The 8 speed ZF used in the Bmw will often match the manual car with economy figures and emissions.

But a X1 costs a lot more to kit out to the sport standard.

I'm amazed at the Newbies on here who actually believe what the on board display is telling them, surely you guys know you're being hoodwinked, there have been so many posts on here to that effect..?

The only true way to calculate MPG is to record actual litres put into the tank against mileage covered, and, believe me, you will find a significant discrepancy between what the display tells you, and what you are getting in real life, fact.

Cat.

I amazed that you actually think brim to brim is accurate, it isn't.
As I have already posted my A4 was only around 1mpg high, which isn't really worth carrying out brim to brim checks.

Once I do establish the error for my car I won't be doing brim to brim refills very often if at all, it uses more fuel carrying more weight than required.

The only accurate way to establish a real mpg reading is to use calibrated instruments, only whatcar does that.

Who mentioned brim to brim filling, not me..?

I record actual litres put in the tank taken from the fuel receipt against the mileage reading every time I fill up, then enter these onto a spreadsheet to calculate the true MPG, which is generally about 10% below the reading on the on-board computer, try it for yourself..?

Cat.

[Bert321]

I reckon brim to brim checking is about as accurate as I can do, I do the math by how much fuel I've used over the distance the car says I've travelled.  However I've often wondered if the milometer on cars over-reads as much as the speedo, since that could make quite a difference.

[xtrailman]

The fuel you buy should be near enough accurate, although temperature makes a difference apparently.
Now if you could then use the sat signal for actual mileage covered, that should be reasonable accurate also, providing you don't use too many hills on the route. 

[skippa]

I record actual litres put in the tank taken from the fuel receipt against the mileage reading every time I fill up, then enter these onto a spreadsheet to calculate the true MPG, which is generally about 10% below the reading on the on-board computer, try it for yourself..?

I use Fuel Buddy - a free Android app on my phone - it saves the bother with spreadsheets and provides some other useful information too.

[Caldean]

Has anyone established whether the Ron rating of petrol makes any difference in the mpg. I filled up with Tesco Momentum before going to Inverness, then Oban, up to Glencoe and back home, filling up at Morrisons  in Fort William with their ordinary fuel. I reckon I got about 5 mpg more with the 98 Ron fuel from Tesco, so even taking road conditions into account (drove through the height of storm Desmond - great choice to have a holiday, I know !) there was a noticeable difference. And before you ask, I went by the gauge,  not brim to brim, or calibrated measurements, spreadsheets.. etc. . So it's anecdotal but maybe someone can verify or debunk the premise that premium fuels are better than supermarket fuel with no additives in terms of mpg and engine protection,  considering the price differential.  Generally I fill up with premium fuel on a one in four basis.

[xtrailman]

It does make a difference with cars designed to run on it.

I had a 180bhp Audi Quattro which was designed for 98, but 95% of the time i used ordinary with a resulting minor power drop.
Nobody could actually tell me what the reduction was, and the only way i could tell was via the front wheels tending to spin during launch off at islands etc.

It wasnt economical with either fuel, 28mpg locally, 33mpg on a run from a car only about 1500kg from memory. Those are brim to brim figures.

[Caldean]

I had the front wheel drive A5 180bhp coupe which suffered from dreadful torque steer as it tried to put the power down through the front tyres. Sorted the worst of it by changing the Dunlop Sportmaxx  tyres with Goodyear AS 2 tyres ... don't think the fuel made much difference  at all.

[tom99]

I have had my 150bhp 2.2 diesel SE-L CX5 from new and now done just over 40,000 miles. I, also, have kept a record of fuel fills by recording the volume fill up at the pumps.
My overall lifetime average is 44.5 mpg. Driving is mixed but includes several 1000 mile long return motorway trips to Scotland from Hampshire in which I barely get 40mpg.
However, my main point is that everytime the car has come out from a service the fuel consumption has decreased

up to 1st service           45.75mpg
up to 2nd service   45.08mpg
up to 3rd service   43.88mpg
since   3rd service        41.90mpg

I am surprised because I have always thought the mpg should improve as the engine loosens. It has always been serviced at the Mazda dealer who say they don't touch anything that should make a change.
Anybody else observed this?

[xtrailman]

I have had my 150bhp 2.2 diesel SE-L CX5 from new and now done just over 40,000 miles. I, also, have kept a record of fuel fills by recording the volume fill up at the pumps.
My overall lifetime average is 44.5 mpg. Driving is mixed but includes several 1000 mile long return motorway trips to Scotland from Hampshire in which I barely get 40mpg.
However, my main point is that everytime the car has come out from a service the fuel consumption has decreased

up to 1st service           45.75mpg
up to 2nd service   45.08mpg
up to 3rd service   43.88mpg
since   3rd service        41.90mpg

I am surprised because I have always thought the mpg should improve as the engine loosens. It has always been serviced at the Mazda dealer who say they don't touch anything that should make a change.
Anybody else observed this?

I had the same thing with my last car.

43mpg before ist service, then down to 41 after, as you say very strange.
Current car is on around 38mpg at the moment.