Author Topic: MPG for those interested.  (Read 172724 times)

peteo48

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Re: MPG for those interested.
« Reply #225 on: September 01, 2018, 10:41:13 PM »
44mpg (calculated brim to brim) over the last 211 miles, mainly short journeys, although a steady cruise to Glasgow and Back along the M8 (50mpg according to trip computer for that trip). 

Trip computer showed 48.1mpg average for the 211 miles.  So quite a difference between trip computer & average mpg as calculate from brim to brim fills. (2013 MK2 Jazz 1.4 EX Plus).

About right Brian. Some people get nearer the computer - say 5% out - but 10% - give or take - is the discrepancy with this car and the 2 previous Jazzes I've owned. In fact 4 mpg over optimistic is about right and this over 12,000 miles in 3 different cars.

In fact I don't really need to do the OCD recording thing that I do. Just look at the computer calculation - deduct 4 mpg and I'm almost blob on.

culzean

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Re: MPG for those interested.
« Reply #226 on: September 02, 2018, 10:09:55 AM »
44mpg (calculated brim to brim) over the last 211 miles, mainly short journeys, although a steady cruise to Glasgow and Back along the M8 (50mpg according to trip computer for that trip). 

Trip computer showed 48.1mpg average for the 211 miles.  So quite a difference between trip computer & average mpg as calculate from brim to brim fills. (2013 MK2 Jazz 1.4 EX Plus).

About right Brian. Some people get nearer the computer - say 5% out - but 10% - give or take - is the discrepancy with this car and the 2 previous Jazzes I've owned. In fact 4 mpg over optimistic is about right and this over 12,000 miles in 3 different cars.

In fact I don't really need to do the OCD recording thing that I do. Just look at the computer calculation - deduct 4 mpg and I'm almost blob on.

The smoother your driving the closer the displayed mpg gets to real mpg, the display gets updated with a snapshot of current usage about every 10 seconds, anything that happens in time since last update (harsh acceleration etc will be ignored) this is typical of industrial 'rate' meters as well (the more you pay for them the higher the refresh / update rate). The on-board one uses the injector open times from ECU and miles on the 'A' trip to calculate mpg. The on-board display is most sensitive to change up to about 50 miles, after that it gets sluggish to register change in driving style as it averages present instantaneous use over miles on trip. I reset trip every time I fill up, that way I can see miles per half tank (rarely let tank get much less than half empty).
« Last Edit: September 02, 2018, 02:09:32 PM by culzean »
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

peteo48

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Re: MPG for those interested.
« Reply #227 on: September 02, 2018, 11:00:20 AM »
I guess, almost by definition, stop start motoring in heavyish traffic is going to be less smooth. I was interested in this so had a look back at some manual records I used to keep before I signed up with Fuelly.com. There is no doubt that the longer trips seemed closer to the real mpg. A recorded 62.4 at one point in my 2010 Jazz was a real 58.6 (3.8 miles out). More typically the recorded mpg would be 44 and the actual 40.

That's where I got my 4 mpg out figure from. It always seemed to be 4 miles (ish) optimistic but that 4 mpg was 6% on longer trips and 10% on the stop start stuff.

andruec

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Re: MPG for those interested.
« Reply #228 on: September 02, 2018, 05:34:55 PM »
I reset trip every time I fill up, that way I can see miles per half tank (rarely let tank get much less than half empty).
Are you aware there's a function to automatically reset Trip A on refueling?

culzean

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Re: MPG for those interested.
« Reply #229 on: September 02, 2018, 06:42:03 PM »
I reset trip every time I fill up, that way I can see miles per half tank (rarely let tank get much less than half empty).
Are you aware there's a function to automatically reset Trip A on refueling?

Thanks for reminder, but it takes a five second press of sel/reset button and occasionally on longer trips I leave trip untouched and will make a note of fuel put in and mileage (and yes I know there is a B trip as well but I never use it). I leave A trip and average mpg showing all the time...
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

guest4871

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Re: MPG for those interested.
« Reply #230 on: September 03, 2018, 10:06:37 AM »
Are you aware there's a function to automatically reset Trip A on refueling?

How do you do that please?

ColinS

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Re: MPG for those interested.
« Reply #231 on: September 03, 2018, 11:11:35 AM »
For the MKIII it is on page 133 of the user manual:
Toggles between When Refueled, When Ignition Is Turned Off and Manual Reset
« Last Edit: September 03, 2018, 11:14:17 AM by ColinS »

andruec

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Re: MPG for those interested.
« Reply #232 on: September 22, 2018, 03:30:30 PM »
I thought the 500 miles estimate was silly. Orange light came on at 410 miles with two bars on the fuel gauge. Finally filled up with the car saying 4 miles left, put in 35 litres. Pump to pump mpg was 55.9.

Bit of a pain. That means a full tank only has enough fuel for two week's commuting plus visiting two local golf courses..and even then I have to drive several miles with the warning light on. The sooner they fix that bridge and re-open the A422 the better :(

Downsizer

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Re: MPG for those interested.
« Reply #233 on: September 22, 2018, 09:36:57 PM »
I thought the 500 miles estimate was silly. Orange light came on at 410 miles with two bars on the fuel gauge. Finally filled up with the car saying 4 miles left, put in 35 litres. Pump to pump mpg was 55.9.
I'm very surprised you could only put in 35 litres if the miles remaining was down to 4.
« Last Edit: September 22, 2018, 09:39:42 PM by Downsizer »

andruec

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Re: MPG for those interested.
« Reply #234 on: September 22, 2018, 09:51:39 PM »
I thought the 500 miles estimate was silly. Orange light came on at 410 miles with two bars on the fuel gauge. Finally filled up with the car saying 4 miles left, put in 35 litres. Pump to pump mpg was 55.9.
I'm very surprised you could only put in 35 litres if the miles remaining was down to 4.
This whole tank has been weird. I mentioned in another thread that a closed road has resulted in me commuting by dual carriageway and motorway instead of A road. That has bumped the displayed mpg from 54 to nearly 58 and for most of the tank the car has been suggesting I'd get nearly 500 miles before filling up. Then for the final quarter it has started reducing that estimate.

At the start of today's drive to golf (21 miles each way) the gauge showed two bars and it predicted 58 miles remaining. At the start of the return journey as I pulled out of the club the fuel light came on and it was saying 27 miles remaining. Then as I pulled up to the pump at journey's end it was saying 4 miles.

It seems like some kind of correction for the overestimate at the start of the tank. Since I could only get 35 litres in (and I had to push it a bit to get that) there suggests there should have been 7 litres left which is over 70 miles of driving.

This is why I normally fill up at half or two thirds empty - to avoid this kind of fuel gauge silliness :-/
« Last Edit: September 22, 2018, 09:54:50 PM by andruec »

culzean

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Re: MPG for those interested.
« Reply #235 on: September 23, 2018, 11:11:35 AM »
I thought the 500 miles estimate was silly. Orange light came on at 410 miles with two bars on the fuel gauge. Finally filled up with the car saying 4 miles left, put in 35 litres. Pump to pump mpg was 55.9.
I'm very surprised you could only put in 35 litres if the miles remaining was down to 4.

It seems logical that the fuel light comes on with about 5 or 6 litres left in tank,  and once you are onto reserve fuel the 'miles to go display' is effectively in negative equity so will say zero until you fill up again.

That is why first half of tank always lasts longer than second half on any car - if tank holds 40 litres then when the gauge is on halfway mark you have used 20 litres (or maybe more if you count that there may be some extra in the tube from filler to tank, but that would be on top of normal 40 litres capacity anyway), the second half of tank will show empty and put the light on when about 14 litres have been used, the other 6 is 'reserve' - ie still there when tank is effectively empty as far as instruments are concerned.
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

Jocko

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Re: MPG for those interested.
« Reply #236 on: September 23, 2018, 11:32:45 AM »
Another thing I have found with my Jazz is once the fuel light comes on it stays on, until you have put sufficient fuel in to reset it. it obviously has a designed in hysteresis. Previous cars I have owned, the fuel light would start flashing on bends, or under braking, and didn't stay lit until a few miles after the first blink. My Jazz doesn't work that way. The light comes on under braking or cornering, then stays on until I fill up. It is either on longer, or is set for a much lower level.
When I went to buy the car the light was on, it was on for the extended test drive, and when the guy came to pick me up to complete the sale it was still on. About 50 miles from my first drive of the car. He then filled up on the return back to his sales room.

andruec

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Re: MPG for those interested.
« Reply #237 on: September 25, 2018, 04:27:09 PM »
Got back from my trip to North Wales (~190 miles each way plus some local travel). Crappy weather going up, good weather coming down. Car claimed 28 miles left on fill. 32 litres squeezed in. 420 miles between fills and 59mpg.

Make of that what you will :-/

As it happens Tesco Brackley only had Momentum fuel left so will be interesting to see how that performs :-/

Downsizer

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Re: MPG for those interested.
« Reply #238 on: September 26, 2018, 10:06:05 PM »
Got back from my trip to North Wales (~190 miles each way plus some local travel). Crappy weather going up, good weather coming down. Car claimed 28 miles left on fill. 32 litres squeezed in. 420 miles between fills and 59mpg.

Make of that what you will :-/

As it happens Tesco Brackley only had Momentum fuel left so will be interesting to see how that performs :-/
What was the computer showing for fuel consumption?

andruec

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Re: MPG for those interested.
« Reply #239 on: September 26, 2018, 10:23:03 PM »
Got back from my trip to North Wales (~190 miles each way plus some local travel). Crappy weather going up, good weather coming down. Car claimed 28 miles left on fill. 32 litres squeezed in. 420 miles between fills and 59mpg.

Make of that what you will :-/

As it happens Tesco Brackley only had Momentum fuel left so will be interesting to see how that performs :-/
What was the computer showing for fuel consumption?
Computer was showing just under 57mpg.

Unusual for it to be underestimating but after the drive up it was only showing 55mpg. Most of the drive up was in heavy rain so that obviously had an effect.

Interestingly the mpg is currently showing as 59.7 which is better than the previous tank. Too early to tell but that suggests better fuel consumption from Momentum.

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