www.tdiclub.com

Economy - Longevity - Performance
The #1 Source of TDI Information on the Web!
Forums Articles Links Meets
Orders TDI Club Cards TDIFest 2016 Gone, but not forgotten VAG-Com List Unit Conversions TDIClub Chat Thank You

Order your TDIClub merchandise and help support TDIClub


Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKVII-Mk7 Golf family including Golf Wagon (~ 2015 +)

VW MKVII-Mk7 Golf family including Golf Wagon (~ 2015 +) Discussions area for the Mk7 (2015+) Golf and Golf Wagon TDIs based on the MQB (Modularer Querbaukasten) platform.

Reply
 
Thread Tools
Old October 21st, 2019, 20:49   #1
jadney
Newbie
 
Join Date: Nov 2014
Location: Madison, WI
Default Gas Mileage: What my TDi says, vs reality

I've had 3 TDi wagons, a 2011 and 2 2015s. The 2 2015s were both purchased from a VW dealer after a Dieselgate buyback and modification.
For decades, I've kept a log of every fuel fillup, on every car I've owned since my '62 Beetle, so I could calculate gas mileage. I've always found this to be a good way to encourage good driving habits and to spot problems before they became obvious.
The diesel mileage that the 2011 calculated almost always matched the mileage I calculated, but the 2015s always display a mi/gal that is way optomistic. It's especially off at the high end. I've had a few tanks that the car tried to tell me that it was getting close to, or above, 60 mi/gal. When I run the numbers, the actual mileage is seldom above 50. On average, I'd say that the car's numbers are 5-10 mi/gal higher than actual.
I noticed this on our first 2015 and assumed it was just this car's sample variation, but that car got totaled by someone not paying attention to the road ahead of him. So we bought the second 2015. It puts out very similar numbers. It appears to me that VW is cooking the books to make it look like their modifications have actually improved the diesel mileage. It's not real.
What we're actually getting is maybe 42-45 on the highway. That's not bad, and I'm not complaining, but the 2011 proved that accurate calculations are possible and VW had the competence to do it. It appears that they have slipped up and failed to do as well with the 2015s.
We're on another long trip right now, and I just noticed another error. On the 2015s, I can look at 3 different mileage numbers: Since Start, Since Refuel, and Extended Period. If I fill up in the morning and then drive for a couple hours without stopping, the Since Start and Since Refuel should be exactly the same. They are not. I forget which is larger, but one was about 1.1 mi/gal larger than the other. That's WAY too much to be explained as a rounding error, or any other kind of excusable error.
There are clearly several problems with the calculation VW has programmed into these cars.
Has anyone else noticed this problem?
jadney is offline   Reply With Quote
Old October 21st, 2019, 21:06   #2
ProfBrown
Veteran Member
 
Join Date: Jan 2019
Location: So Cal
Fuel Economy: In the sig
Default

Quote:
Originally Posted by jadney View Post
I've had 3 TDi wagons, a 2011 and 2 2015s. The 2 2015s were both purchased from a VW dealer after a Dieselgate buyback and modification.

For decades, I've kept a log of every fuel fillup, on every car I've owned since my '62 Beetle, so I could calculate gas mileage. I've always found this to be a good way to encourage good driving habits and to spot problems before they became obvious.

The diesel mileage that the 2011 calculated almost always matched the mileage I calculated, but the 2015s always display a mi/gal that is way optomistic. It's especially off at the high end. I've had a few tanks that the car tried to tell me that it was getting close to, or above, 60 mi/gal. When I run the numbers, the actual mileage is seldom above 50. On average, I'd say that the car's numbers are 5-10 mi/gal higher than actual.

I noticed this on our first 2015 and assumed it was just this car's sample variation, but that car got totaled by someone not paying attention to the road ahead of him. So we bought the second 2015. It puts out very similar numbers. It appears to me that VW is cooking the books to make it look like their modifications have actually improved the diesel mileage. It's not real.

What we're actually getting is maybe 42-45 on the highway. That's not bad, and I'm not complaining, but the 2011 proved that accurate calculations are possible and VW had the competence to do it. It appears that they have slipped up and failed to do as well with the 2015s.

We're on another long trip right now, and I just noticed another error. On the 2015s, I can look at 3 different mileage numbers: Since Start, Since Refuel, and Extended Period. If I fill up in the morning and then drive for a couple hours without stopping, the Since Start and Since Refuel should be exactly the same. They are not. I forget which is larger, but one was about 1.1 mi/gal larger than the other. That's WAY too much to be explained as a rounding error, or any other kind of excusable error.

There are clearly several problems with the calculation VW has programmed into these cars.

Has anyone else noticed this problem?


The ďsince startĒ is a bs measurement. Itís not since you started the car on that run cycle, itís since you started driving within a certain amount of time. What that 1.1 miles is, is your distance from your driveway/wherever you park the car, to the gas station where you filled up. Iíve noticed it still saying ďsince startĒ even with the car sitting off in the parking lot for 30 minutes. I dont know why itís done this way, sort of misleading, but to answer your question thatís the discrepancy. This is assuming of course you drove to a gas pump before driving the rest of that morning..

For what itís worth, no car I have ever owned with an mpg reader was very accurate. Always they say a few points better than they are actually getting. My 15 GSW is about the same, only a few points off. 5 at most. I just look at the display, and guess a few points low and usually Iím spot on. My truck was usually 2 mpg points high.


Sent from my iPhone using Tapatalk
__________________
2015 GSW TDI SE DSG

DON'T TRACK THIS ANYMORE
ProfBrown is offline   Reply With Quote
Old October 21st, 2019, 21:16   #3
RIP TDI
Veteran Member
 
Join Date: Feb 2000
Location: Santa Barbara, CA
Default

MFA consumption readout on the Mk 7s is typically somewhere around 6 - 8% optimistic. The error can be reduced to in the range of 1% optimistic to 1% pessimistic using VCDS.

Your Since Start and Since Refuel reading would only be identical if you manually reset the Since Start right after you filled up.
__________________
- Chris
'15 GSW SE 6MT, '01 Golf 5MT
'97 Passat sedan, '96 Passat variant
'99 BMW M3 Cabrio
RIP TDI is offline   Reply With Quote
Old October 21st, 2019, 21:23   #4
RIP TDI
Veteran Member
 
Join Date: Feb 2000
Location: Santa Barbara, CA
Default

Quote:
Originally Posted by ProfBrown View Post
The “since start” is a bs measurement. It’s not since you started the car on that run cycle, it’s since you started driving within a certain amount of time. What that 1.1 miles is, is your distance from your driveway/wherever you park the car, to the gas station where you filled up. I’ve noticed it still saying “since start” even with the car sitting off in the parking lot for 30 minutes. I dont know why it’s done this way, sort of misleading
VW MFAs have had the Since Start value forever and its legit. It automatically resets after sitting off for 2+ hours, but runs continuously up to a large max value as long as the car is running, including off periods of less than 2 hours between running periods.
__________________
- Chris
'15 GSW SE 6MT, '01 Golf 5MT
'97 Passat sedan, '96 Passat variant
'99 BMW M3 Cabrio
RIP TDI is offline   Reply With Quote
Old October 21st, 2019, 21:25   #5
ProfBrown
Veteran Member
 
Join Date: Jan 2019
Location: So Cal
Fuel Economy: In the sig
Default

Quote:
Originally Posted by RIP TDI View Post
VW MFAs have had the Since Start value forever and its legit. It resets after sitting off for 2+ hours, but runs indefinitely as long as the car is running, including off periods of less than 2 hours between running periods.


Couple points I should make, this is my first VW that is newer than 1973, and second my claim that itís ďBSĒ is due to it being called ďSince StartĒ when itís not per start. Itís essentially per driving leg of a journey, apparently if the stop is less than 2 hours the car reads as if it never stopped which is counterintuitive to the name.

Makes more sense now with your clarifying post, and for that I thank you. But from a newbie to the car thatís why I said it was BS LMAO.


Sent from my iPhone using Tapatalk
__________________
2015 GSW TDI SE DSG

DON'T TRACK THIS ANYMORE
ProfBrown is offline   Reply With Quote
Old October 22nd, 2019, 05:19   #6
jadney
Newbie
 
Join Date: Nov 2014
Location: Madison, WI
Default

Quote:
Originally Posted by RIP TDI View Post
MFA consumption readout on the Mk 7s is typically somewhere around 6 - 8% optimistic. The error can be reduced to in the range of 1% optimistic to 1% pessimistic using VCDS.
What I see, on both of the 2015s that I've had is an error of more like 20%. That's when the car says 60 mi/gal but the actual number comes out to 50.

Okay, revealing my ignorance, what is VCDS?
jadney is offline   Reply With Quote
Old October 22nd, 2019, 05:52   #7
oilhammer
Certified Volkswagen Nut Vendor
 
oilhammer's Avatar
 
Join Date: Dec 2001
Location: St Louis
Fuel Economy: fantastic
Default

I have found over the years that the MFA's fuel economy trends closer to accurate the longer the trip is. So for shorter trips (less than 100 miles) it trends to 5-8% higher than actual, but for a 500 mile trip it ends up closer to 2-3% accurate. But it is always on the side of optimistic. Plus, it is going by the fuel measured by the ECU as being injected into the engine, not by fuel gauge position, although gauge position is what the MFA uses to calculate "distance to refueling". Which I always get a kick out of when you start out with a full, vented tank, because THAT value goes UP for the first ~50-100 miles.
__________________
oilhammer
www.cardocautomotive.com
oilhammer is offline   Reply With Quote
Old October 22nd, 2019, 07:49   #8
IndigoBlueWagon
TDIClub Enthusiast
Principal IDParts
Vendor
w/Business number
 
Join Date: Aug 2004
Location: South of Boston
Fuel Economy: 50/45/37
Default

I adjusted the FE readout in the cluster in my '15 GSW using VCDS to 7% lower than it was reading. Pretty dead on now, maybe 1 MPG low for a full tank. There are instructions here somewhere on how to do it.

My BMW consistently reads 2-3 MPG low. And to the best of my knowledge I can't adjust it.

Honestly, I find the cluster FE readings annoying. I prefer to have a rough idea of how I'm doing by reading the fuel gauge, and then calculating FE when refilling. Less stressful.
__________________
2002 Jetta wagon, 400K, RC3+; 1993 Mercedes-Benz 300D 2.5, 197K; 1997 Passat, 289K; '99.5 Golf, 260K; 2011 335d, 63K; 2015 Golf Sportwagen, 13K. Principal, http://www.idparts.com
Kid's cars: 2002 Golf TDI, 2002 Jetta TDI, 2015 Passat TDI SEL
IndigoBlueWagon is offline   Reply With Quote
Old October 22nd, 2019, 08:01   #9
KERMA
 
KERMA's Avatar
 
Join Date: Sep 2001
Location: here
Default

in b4 "your car doesn't use gas so no gas mileage"

the accepted verbiage around here is "fuel economy" FWIW
__________________
HP is for show, TQ is for go.
celebrating http://www.kermatdi.com since 2002
kermatdi on facebook
No, no, you're not thinking; you're just being logical. - Neils Bohr
KERMA is offline   Reply With Quote
Old October 22nd, 2019, 08:19   #10
RIP TDI
Veteran Member
 
Join Date: Feb 2000
Location: Santa Barbara, CA
Default

Quote:
Originally Posted by ProfBrown View Post
Couple points I should make, this is my first VW that is newer than 1973, and second my claim that itís ďBSĒ is due to it being called ďSince StartĒ when it’s not per start. Itís essentially per driving leg of a journey, apparently if the stop is less than 2 hours the car reads as if it never stopped which is counterintuitive to the name.

Makes more sense now with your clarifying post, and for that I thank you. But from a newbie to the car thatís why I said it was BS LMAO.


Sent from my iPhone using Tapatalk
I take your point. On the older A3/B4/A4s, it was called "Trip 1" instead of "Since Start" and "Trip 2" instead of "Extended Period". Less misleading in some ways, more so in others.
__________________
- Chris
'15 GSW SE 6MT, '01 Golf 5MT
'97 Passat sedan, '96 Passat variant
'99 BMW M3 Cabrio
RIP TDI is offline   Reply With Quote
Old October 22nd, 2019, 08:25   #11
RIP TDI
Veteran Member
 
Join Date: Feb 2000
Location: Santa Barbara, CA
Default

Quote:
Originally Posted by jadney View Post
Okay, revealing my ignorance, what is VCDS?
Get used to searching here; there's a wealth of info on this site.
__________________
- Chris
'15 GSW SE 6MT, '01 Golf 5MT
'97 Passat sedan, '96 Passat variant
'99 BMW M3 Cabrio
RIP TDI is offline   Reply With Quote
Old October 22nd, 2019, 08:32   #12
1854sailor
Resident Curmudgeon
 
1854sailor's Avatar
 
Join Date: Aug 2004
Location: Baltimore, MD
Fuel Economy: Great!
Default

Quote:
Originally Posted by jadney View Post
...Okay, revealing my ignorance, what is VCDS?
You've been around this site since 2014 and you've never heard of VCDS??
__________________
Never wrestle with pigs. You both get dirty and the pig likes it.
-George Bernard Shaw
1854sailor is offline   Reply With Quote
Old October 22nd, 2019, 08:47   #13
RIP TDI
Veteran Member
 
Join Date: Feb 2000
Location: Santa Barbara, CA
Default

Quote:
Originally Posted by oilhammer View Post
I have found over the years that the MFA's fuel economy trends closer to accurate the longer the trip is. So for shorter trips (less than 100 miles) it trends to 5-8% higher than actual, but for a 500 mile trip it ends up closer to 2-3% accurate. But it is always on the side of optimistic. Plus, it is going by the fuel measured by the ECU as being injected into the engine, not by fuel gauge position, although gauge position is what the MFA uses to calculate "distance to refueling". Which I always get a kick out of when you start out with a full, vented tank, because THAT value goes UP for the first ~50-100 miles.
Well, of course the ECU infers fuel flow from a variety of data rather than actually measures it, and that is the source of the non-linear error you mention.

My understanding is that "distance to refueling" uses inferred accumulated fuel used rather than gauge position for calculation, at least on the Mk 7. And that also explains the phenomenon you describe. The beginning value after a fill up is based on the calculated value from the previous tank and gets adjusted by inferred current fuel flow rate, which can be lower or higher than the average rate of the previous tank.
__________________
- Chris
'15 GSW SE 6MT, '01 Golf 5MT
'97 Passat sedan, '96 Passat variant
'99 BMW M3 Cabrio
RIP TDI is offline   Reply With Quote
Old October 22nd, 2019, 08:51   #14
RIP TDI
Veteran Member
 
Join Date: Feb 2000
Location: Santa Barbara, CA
Default

Quote:
Originally Posted by 1854sailor View Post
You've been around this site since 2014 and you've never heard of VCDS??
Ha, I knew someone would take it a step further than I did and should have guessed it would be you, Sailor
__________________
- Chris
'15 GSW SE 6MT, '01 Golf 5MT
'97 Passat sedan, '96 Passat variant
'99 BMW M3 Cabrio
RIP TDI is offline   Reply With Quote
Old October 22nd, 2019, 08:57   #15
IndigoBlueWagon
TDIClub Enthusiast
Principal IDParts
Vendor
w/Business number
 
Join Date: Aug 2004
Location: South of Boston
Fuel Economy: 50/45/37
Default

Maybe not apropos of much in this discussion, but I took this photo this AM because I liked the even numbers of fuel used and remaining.

It also shows I haven't driven the car much in the two and a half year's I've owned it.
__________________
2002 Jetta wagon, 400K, RC3+; 1993 Mercedes-Benz 300D 2.5, 197K; 1997 Passat, 289K; '99.5 Golf, 260K; 2011 335d, 63K; 2015 Golf Sportwagen, 13K. Principal, http://www.idparts.com
Kid's cars: 2002 Golf TDI, 2002 Jetta TDI, 2015 Passat TDI SEL
IndigoBlueWagon is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Incredible A6 TDI gas mileage Jonarchen TDI Fuel Economy 9 October 12th, 2017 23:15
tdi gas mileage/ 1/4 tank.. Ichance405 VW MKVI-A6 Golf family including Jetta SportWagen (~ 2010-2014) 35 September 10th, 2011 07:01
Gas mileage on 2005 TDI Beetle Debbie martz New Beetle TDI Picture Gallery 28 September 15th, 2007 17:21
gas mileage on new Golf TDI Giovanni TDI Fuel Economy 4 August 2nd, 2002 15:35
Jetta TDI Gas Mileage flfirefighter27 TDI Fuel Economy 11 May 23rd, 2000 18:15


All times are GMT -7. The time now is 16:26.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright - TDIClub Online LTD - 2017
Contact Us | Privacy Statement | Forum Rules | Disclaimer
TDIClub Online Ltd (TDIClub.com) is not affiliated with the VWoA or VWAG and is supported by contributions from viewers like you.
© 1996 - 2017, All Rights Reserved
Page generated in 0.18391 seconds with 13 queries
[Output: 138.23 Kb. compressed to 116.81 Kb. by saving 21.42 Kb. (15.50%)]