New car....mpg vs maths....surely not?
Discussion
Picked up a new car, and filled it to the brim.
Along the way, this average mpg was recorded for posterity.....
I consider maths to be one of my strong points, but for the life of me, I'm struggling to make sense of the result!
Travelled from near Aylesbury to Dumfries along the M40 & M6, sitting mostly between 60-65 mph with the cruise engaged.
Didn't make an exact note of the mileage or fuel gauge, but recall it was circa half full.
First and only time trying Momentum 99, it was filled up again (or what seemed to be indicated by the pump clicking a couple of times) with 23.5L of the stuff.
The gauge didn't show fully filled, so if we assume another 3.5 litres may've been able to be fitted in, then the 313 mile journey, with one stop at a service station just before Carlisle for emptying myself and filling the tyres after the monitor system threw up a CHECK message, was covered with 27L of Esso's finest regular 95.
Now this is where my puzzlement arises from - the onboard suggested 41 ish mpg average, but the maths indicates 52.7 mpg, including the stationary & stop/start element in Dumfries town whilst navigating to the Tesco station.
If this is correct, then that's one helluva feat for a 3L V6 one of these.....
Along the way, this average mpg was recorded for posterity.....
I consider maths to be one of my strong points, but for the life of me, I'm struggling to make sense of the result!
Travelled from near Aylesbury to Dumfries along the M40 & M6, sitting mostly between 60-65 mph with the cruise engaged.
Didn't make an exact note of the mileage or fuel gauge, but recall it was circa half full.
First and only time trying Momentum 99, it was filled up again (or what seemed to be indicated by the pump clicking a couple of times) with 23.5L of the stuff.
The gauge didn't show fully filled, so if we assume another 3.5 litres may've been able to be fitted in, then the 313 mile journey, with one stop at a service station just before Carlisle for emptying myself and filling the tyres after the monitor system threw up a CHECK message, was covered with 27L of Esso's finest regular 95.
Now this is where my puzzlement arises from - the onboard suggested 41 ish mpg average, but the maths indicates 52.7 mpg, including the stationary & stop/start element in Dumfries town whilst navigating to the Tesco station.
If this is correct, then that's one helluva feat for a 3L V6 one of these.....
Edited by PJ S on Monday 16th July 14:04
Your convoluted description of filling doesn't make a lot of sense but it sounds like you are calculating it off the fuel guage havig guessed at 27 litres between full and half.
The only way to get an accurate measurement is the 'brim to brim' metthod. Brim it, drive, brim again. Use that voulme of fuel in your calcuation.
The only way to get an accurate measurement is the 'brim to brim' metthod. Brim it, drive, brim again. Use that voulme of fuel in your calcuation.
Yes, but the head scratching comes from normally the OBC is a bit optimistic with its calculations, whereas the maths was showing it to be wildly pessimistic.
Either way, 40 odd on a long run at a nice steady pace, isn't to be sniffed at in a luxo-barge such as this.
Certainly vindicates the decision to go for it rather than the E65 745 I'd lined up, but fell through at almost the last minute.
It's only taken another 8 months to get to this point, and nearly a year since I'd considered but dismissed the GS over the foot operated parking brake as being a compromise I couldn't accept.
Funny how things change in that regard.....?
Either way, 40 odd on a long run at a nice steady pace, isn't to be sniffed at in a luxo-barge such as this.
Certainly vindicates the decision to go for it rather than the E65 745 I'd lined up, but fell through at almost the last minute.
It's only taken another 8 months to get to this point, and nearly a year since I'd considered but dismissed the GS over the foot operated parking brake as being a compromise I couldn't accept.
Funny how things change in that regard.....?
On all my cars the lower end of the fuel gauge done considerably less miles than the top half of the gauge. Doesn't make much sense so let's say I filled the car up and drove 300 miles to half a tank, after that I only done 200 miles on the lower half of the tank. My CTR was the worse with bottom half emptying in 40 minutes 
Captain Muppet said:
PJ S said:
I consider maths to be one of my strong points, but for the life of me, I'm struggling to make sense of the result!
You divided one assumed number by another assumed number and don't believe your answer.I'm not sure maths really is one of your strong points.
Sorry.
PJ S said:
Yes, but the head scratching comes from normally the OBC is a bit optimistic with its calculations, whereas the maths was showing it to be wildly pessimistic.
The maths showed nothing. The OBC may well be optimistic, like most, but you won't know until you do a proper MPG check. Basing any mpg calculation on the fuel gauge will introduce a huge source of error given the inaccuracy and non liniarity (at least in my experience) of most gauges.Captain Muppet said:
You divided one assumed number by another assumed number and don't believe your answer.
I'm not sure maths really is one of your strong points.
I'm not sure maths really is one of your strong points.
I'm not saying Google maps is 100% accurate, but the numbers do stack up in relation to the trip reading upon arrival at Cairnryan.
You're right in that I am assuming the difference between Aylesbury's level and Dumfries' was 3 litres, but I honestly don't believe that would be far from the truth.
PJ S said:
Captain Muppet said:
You divided one assumed number by another assumed number and don't believe your answer.
I'm not sure maths really is one of your strong points.
I'm not sure maths really is one of your strong points.
I'm not saying Google maps is 100% accurate, but the numbers do stack up in relation to the trip reading upon arrival at Cairnryan.
You're right in that I am assuming the difference between Aylesbury's level and Dumfries' was 3 litres, but I honestly don't believe that would be far from the truth.
If you can't get the maths to include the trip computer then all you can say for certain is that something somewhere is wrong. So do a proper mpg calc, and that will tell you how much the trip computer is lying.
Devil2575 said:
The maths showed nothing. The OBC may well be optimistic, like most, but you won't know until you do a proper MPG check. Basing any mpg calculation on the fuel gauge will introduce a huge source of error given the inaccuracy and non liniarity (at least in my experience) of most gauges.
I'd wholly agree if I were basing it on a calculation from the needle position, and the specs for the car's tank volume - which incidentally is 71 litres.I'm looking at and working off the receipts which show how much fuel I put in, hence where the 23.5L comes from.
I've allowed for the fact I didn't neck the 2nd fill, as I did the 1st (to achieve a round figure of £77).
Having filled the Honda enough times to know when the pumps click, how much more you can realistically get away with adding to bring the cost up to an even £xx.00, the Lexus can't be any different - not least since I'd already done it with the 1st fill up, without petrol overflowing onto the ground.
Therefore the maths is valid - 313 miles for 26.5-27L, which is why I put this thread up.
Even if I'm wrong, and 5L would've been possible to fit into the tank (irrespective of needle positioning), that still equates to a 3L V6 being capable of just under 50mpg - which I think is incredible.
Of course, my normal drives won't be 300 odd miles in a single hop along the motorway, but even if it pans out to be 30-32 mpg, that's still better than what the Honda gave me, when I bothered to calculate it - and it was a manual with 2.4L 4 cylinder.
LeoZwalf said:
You need to get some accurate input numbers first.
Brim it, reset the trip counter.
Drive.
Brim it again, note how many of Esso's finest litres you put in and see how many miles you did since the last brim.
Then see how much difference there is between the OBC and the maths.
^^^^ This. In my experience most on-board fuel computers can barely tell the time.Brim it, reset the trip counter.
Drive.
Brim it again, note how many of Esso's finest litres you put in and see how many miles you did since the last brim.
Then see how much difference there is between the OBC and the maths.
Hi, sorry for thread resurrection, OP how is your average mpg going? I ask as I'm seriously considering one of these as my next car.
Other than MPG, how is it? What's the performance like? I'm not expecting it to be as fast as my S2000 but do want/need something that will easily overtake others on the a/b road commute.
Other than MPG, how is it? What's the performance like? I'm not expecting it to be as fast as my S2000 but do want/need something that will easily overtake others on the a/b road commute.
Having done a calculation based on fuel filled and mileage done to get to the reserve light twice now, it's 32.5 mpg, and that's pretty much in line with the OBC.
Filled it with the second tankful (57.5L) with 19 mile range, managing to overflow it!
Refilled the other day with 56.5L, so referencing the above posts, I am as sure as can be, that I was only about 2L shy at Dumfries from a fully full tank.
Anyway, aside from that - I'm loving every minute of the car, and if you need to overtake, you're not going to struggle when you plant the right foot to activate kickdown mode.
It can fairly shift for a bit of lardy box - but it is a bit wallowy in the tighter bends, so I may be dropping a set of F-Sport springs in it (member discount helps on Club Lexus, but still having to be imported from the US!), and F-Sport ARBs.
Other than that, headroom is a slight issue if it's fitted with the sunroof option on SEs or as standard on the SE-Ls, but with so much else to like about the car, the odd compromise is not hard to put up with.
Compared to your outgoing S2K, it'll be a completely different feel - the weight is definitely very noticeable, but you'd be best to drive one yourself to see if you get on with it.
One thing that has surprised me, is the turning circle - very tight for a big car. Certainly tighter than the Volvo S60's, which I still vividly remember from 7 years ago!
Filled it with the second tankful (57.5L) with 19 mile range, managing to overflow it!
Refilled the other day with 56.5L, so referencing the above posts, I am as sure as can be, that I was only about 2L shy at Dumfries from a fully full tank.
Anyway, aside from that - I'm loving every minute of the car, and if you need to overtake, you're not going to struggle when you plant the right foot to activate kickdown mode.
It can fairly shift for a bit of lardy box - but it is a bit wallowy in the tighter bends, so I may be dropping a set of F-Sport springs in it (member discount helps on Club Lexus, but still having to be imported from the US!), and F-Sport ARBs.
Other than that, headroom is a slight issue if it's fitted with the sunroof option on SEs or as standard on the SE-Ls, but with so much else to like about the car, the odd compromise is not hard to put up with.
Compared to your outgoing S2K, it'll be a completely different feel - the weight is definitely very noticeable, but you'd be best to drive one yourself to see if you get on with it.
One thing that has surprised me, is the turning circle - very tight for a big car. Certainly tighter than the Volvo S60's, which I still vividly remember from 7 years ago!
Thanks.
I'm not expecting thrills like in the S2000 of course, getting to an age where I want something more comfy (long term back problems etc.) that's a little different but is nice/upmarket inside, goes pretty well and is reliable/well built. Not sure if I'm ready to let go of having a sports car yet though
But when I do (in next year I think) the GS is top of my current list.
Anyway, the 430 I like for the performance, the 450H for the performance and economy (but lack of boot space). The 300 (if I can get one with walnut - hate the red wood - and ML stereo for < £10k) probably does all I need and goes well enough without drinking too much. I get 28/30 mpg out of the S2000 so would like similar that can do good economy on the odd m-way trip.
Noted about the sunroof, I am tall so need to see if I really do fit in one well. My uncle as the older shape GS430 and I fit that as I recall so I would imagine the newer model would not be worse in the height department.
How have you found servicing costs?
I'm not expecting thrills like in the S2000 of course, getting to an age where I want something more comfy (long term back problems etc.) that's a little different but is nice/upmarket inside, goes pretty well and is reliable/well built. Not sure if I'm ready to let go of having a sports car yet though
But when I do (in next year I think) the GS is top of my current list.Anyway, the 430 I like for the performance, the 450H for the performance and economy (but lack of boot space). The 300 (if I can get one with walnut - hate the red wood - and ML stereo for < £10k) probably does all I need and goes well enough without drinking too much. I get 28/30 mpg out of the S2000 so would like similar that can do good economy on the odd m-way trip.
Noted about the sunroof, I am tall so need to see if I really do fit in one well. My uncle as the older shape GS430 and I fit that as I recall so I would imagine the newer model would not be worse in the height department.
How have you found servicing costs?
Only just got it, so no idea on that front.
Lexus dealer offered 2 years servicing with 2x MOTs & pre inspection for £575, iirc, via the computer system.
That was for 80 & 90K services, and price frozen once entered into the agreement - so if parts, oil, labour costs increase during those 2 years, it's still only £29 a month.
Thinking of doing that as it probably won't be all that cheaper once OE parts bought.
Also makes it easier to persuade Lexus to offer goodwill if needed.
Think that includes flushes, but not transmission oil change.
Lexus dealer offered 2 years servicing with 2x MOTs & pre inspection for £575, iirc, via the computer system.
That was for 80 & 90K services, and price frozen once entered into the agreement - so if parts, oil, labour costs increase during those 2 years, it's still only £29 a month.
Thinking of doing that as it probably won't be all that cheaper once OE parts bought.
Also makes it easier to persuade Lexus to offer goodwill if needed.
Think that includes flushes, but not transmission oil change.
Gassing Station | General Gassing | Top of Page | What's New | My Stuff