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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old March 5th, 2011, 19:17   #1
bfrinkus
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Default mods and effect on mpg

I LOVE these forums, but have a beef with relative lack of data relating mods to fuel economy. I see a lot of "I did x and got about 10% mpg improvement!". Many claims are unrealistic and don't take into account all possible variables. Here's my approach to make a contribution to these forums:

-all mods are performed by me, but primary driver of the car (1997 jetta tdi sedan 5 spd manual) is my wife. She is not aware of what mods are made or when so this should eliminate placebo effect.
-all "fillups" are comprised of fuel ups of at least 8 gallons.
-all mpgs reported are 3 tank averages directly before/after mod. This should eliminate a one tank outlier where maybe the fuel tank doesn't get filled all the way to the top.
-all fuel ups are as consistent as possible in method.
-my wife's driving routine and habits are pretty dang consistent. She's no hypermiler, but consistently upshifts at 2000 rpm and drives at or 5 over the speed limit.
-I perform 1 mod at a time so as not to confuse results.
-car was purchased used with "high" miles of 216k. Car was dealer maintained and 100% unmodified when purchased.

EGR kit by dieselgeek:
-mpg before 44.9
-mpg after 44.3
-conclusion, not a smart mod if for mpg. However, this is a well made kit that serves an important purpose. I recommend this kit.

Switch from conventional motor oil to synthetic oil:
-mpg before 44.3
-mpg after 44.1
-again, if for mpg only, you're out of luck. There is lots of discussion on here about this topic. I think synthetic is great, read some other posts and see what you think.

Fuel quality: some companies clearly disclose diesel cetane, other companies won't let the cat out of the bag. I switched from bp (company publicly claims to sell diesel with cetane of 40) to QT (neither corporate nor stations can/will tell me what cetane they sell).
-mpg before (bp): 44.1
-mpg after (QT): 46.1
-WOW! I actually set 2 tank mpg records in this 3 tank span. This reinforces the importance of fuel quality on performance of our diesel engines. Again, there are some great posts telling what fuels are what quality. Take the time to find the best fuel in your area...as my experience shows, it may be worth a few miles a gallon!

I recently added MotorKote hyper lubricant to my engine. My gut tells me it's snake oil, but there's only 1 way to find out, huh? If there's anything ya'll want me to try, let me know! If it's cheap and not dangerous in my opinion, I'll do it. If it's expensive and you're willing to foot the bill, I'll do it.

More to come soon...

Best,
Brad
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Old March 6th, 2011, 03:10   #2
Joe_Meehan
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Thanks for the information.
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Old March 6th, 2011, 03:47   #3
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Obviously, there is something going on with your TDI.....seems MPGs are low! The low MPGs could be related to the driving circumstances, i.e. mostly city and mixed vs on the road.

Statistics: I don't think a three tank usage after a mod will actually reflect the data you are looking for, unless the driving circumstances are the same as the previous three tanks..........and were all those tanks actually full...very important! Long term data is more reflective of any results, etc.

EGR mod: I do not have the Diesel Geek EGR, however, I did do the EGR mod via VCDS and the stats I maintain in Excel spreadsheet definitely showed a difference in MPGs. It is very reflective in the numbers as well as the MPG graph!

Oil: Why was conventional oil being used in the engine? I thought it was dealer maintained????? I seriously doubt that switching from the conventional oil to synthetic caused a MPG drop ....just no way!

Fuel: I have always purchased fuel where it is the cheapest...... really have not noticed a difference in the MPGs. I have burned QT diesel (my brother lives in Gainesville, GA ..QT stations there) and did not notice any difference........ lately I've been burning diesel fuel purchased from Kroger supermarket pumps...no noticeable difference.

Additives: I'll get beat over the head for this: In my opinion, most "additives" are snake oil....regardless of the product or name brand! I do not use additives of any kind, unless a very cold weather system is moving in. Then I add Power Service to aid in preventing the fuel from gelling!

I have over 236,000 miles of data in my Excel Speadsheet! The Mod I have done that achieved the best results was to slow my average speed! Of course, other good driving habits can improve fuel economy. Avoiding jack rabbit starts, stay out of drive-thru lines (McDs, Banking, etc.), avoid idling the engine, make the best use of coasting in gear (approaching a stop sign, red traffic light, etc.), draft when possible/appropriate/safe, empty the car of unnecessary junk (weight), keep a skid cover on the bottom of the engine (reduces drag), avoid speeds in excess of 70 mph, avoid driving in lower gear when the next higher will be more appropriate for the circumstances (driving around with the RPMs up unnecessarily), etc.

Back to my first statement: A determination should be made as to whether the car is achieving the best MPGs under the driving circumstances before doing any mods.......i.e., does it need attention to maintenance issues: engine timing, air filter, accumulated oil removed from the Intercooler, Intake manifold & EGR cleaned (probably packed with crud due to using the conventional engine oil), ...........fuel filter? Well, I seriously doubt a new fuel filter will improve MPGs.

Keep us posted!
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Old March 6th, 2011, 14:02   #4
bfrinkus
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andybees, thx for input. To address your concerns:
-all maint up to date ie fresh filters, intake cleaned, snow screen cleaned, ecm parameters set within oem specs, etc. I also regularly check and maintain consistent tire pressures.
-wife's driving routine very consistent. 50 mile round trip daily commute at 60mph with no lights. Small amount of city driving. Fuel ups made in same manner to full each time, ventectomy performed before any mods.
-i agree...neither synthetic oil nor egr delete caused mileage drop. I think small drops or gains are likely statistically irrelevant.
-i also agree that driving style habits are biggest affect on mpg. However, i'm looking for mods to supplement improvements made by driving style.
-i have a theory that pirelli tires are robbing me of several mpgs. I won't know for sure until i swap tires.
-sounds like you have some good data! To all on forum, please share mods you made and thier effect on mpg if you have supportive data.
-most stations sell diesel with cetane of 40 which is why i believe you don't notice mpg difference between brands. However some stations ex: amoco branded BP is 47 cetane, sell higher quality fuel that i'm convinced provides better performance and mpg. Whether costlier fuel is cost effective or not is another question...
Thanks for input!
Brad
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Old March 7th, 2011, 06:33   #5
MikeMars
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Quote:
Originally Posted by bfrinkus View Post
...
-i also agree that driving style habits are biggest affect on mpg. However, i'm looking for mods to supplement improvements made by driving style.
...
This is the problem - it is likely that the data you are generating is dominated by temperature&driving style, rather than reflecting the changes made by your modifications. These two variables dominate all others.
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Old March 7th, 2011, 07:00   #6
VWBeamer
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Did you get a re tune after the egr delete? I went from 38 to about 42 after Egr delete, tune and larger turbo.
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Old March 7th, 2011, 07:55   #7
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Unless you can undo the mod and repeat the results, differences of less than 1 or 2 mpg are typical tank to tank, and cannot be held as significant. Especially if you are not the driver and have no awareness of the driving conditions.
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Old March 7th, 2011, 09:20   #8
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I disagree 1-2 mpg differences are huge. .2 and .8 mpg differences are stistically insignificant and could easly be caused by weather, temp, wind changes. I am guesing that your mpg difference after changing stations is based off the pump inaccuracies. Pumps are allowed to be a certain percentage off. Someone said up to 12%
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Old March 7th, 2011, 10:36   #9
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Quote:
Originally Posted by Nich View Post
I disagree 1-2 mpg differences are huge. .2 and .8 mpg differences are stistically insignificant and could easly be caused by weather, temp, wind changes. I am guesing that your mpg difference after changing stations is based off the pump inaccuracies. Pumps are allowed to be a certain percentage off. Someone said up to 12%
The term huge is subjective. It depends on how much variation there is in the conditions out of your control - traffic, driving conditions, habits, weather, and yes, pump variations. Normal pump variation is limited and tested to 6 cubic inches in 5 gallons -- that's 0.5%. 12% is either a lie or criminal.

Your typical fillup probably varies more depending on how full you fill your tank, so multiple tanks must be averaged to determine the success of a mod.
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Old March 7th, 2011, 14:32   #10
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In order for these tests to be accurate, the drives need to be made consistently with the same driving. Such as taking the same route to work everyday and only driving it then to rule out a bunch of factors. Of course two or three car wrecks on the highway on the way to work could drastically slow you down, and change your mpg. Things that need to be noted since your wife is the unknowing guinea pig, these are things you probably won't factor in.
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Old March 7th, 2011, 22:28   #11
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How about using slightly taller tires? Sure that should help. Same rotation, more distance traveled.
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Old March 8th, 2011, 02:59   #12
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While the car in question is a TDI, it is also worth noting that it's a Mk III. Also, temperature can be a huge variable, especially when using such small samples.
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Old March 9th, 2011, 19:53   #13
bfrinkus
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Wow, loving the response to the thread!

To restate my goal with this little project, my hope is to identify mods that will supplement smart driving and debunk overstated claims of efficiency improvement. Please understand that my R and D budget is very small. With this in mind, i think i've done a fair job minimizing variables well enough to identify statstically relevant trends. I will take into account all suggestions. To address some of them:

-i will review and compare ambient temperature to tank mpg results to see if there is a positive correlation. I'll let you know what i find.
-wife's commute: she takes the same route every day at the same time each day. There is no traffic. Ever. Best commute ever. She drives at to 5mph over. Test track? No, but ya'll are going to have to trust me that it would be hard to create real world driving conditions with fewer variables.
-i have thought about screwing with tire circumference, but have not due to money as well as speedo recalibration issues. In related news, I hope to be installing .681 5th gear in the next few months here.
-re-tune after EGR delete? I don't even know what that is, but i'll look into it.
-fuel volume:i'm aware that the gov allows only minimal inaccuracies in dispensed fuel volumes. I have no way to check this and will have to trust that Uncle Sam is enforcing things.
-Souzafone, i'm newish to the tdi world and did not understand your comment. Would you be so kind to explain what you meant? Thank you!

I invite all others with data to share so we can learn from one another!

Best, Brad
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Old March 9th, 2011, 20:55   #14
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Quote:
Originally Posted by bfrinkus View Post
Wow, loving the response to the thread!
To restate my goal with this little project, my hope is to identify mods that will supplement smart driving and debunk overstated claims of efficiency improvement. Please understand that my R and D budget is very small. With this in mind, i think i've done a fair job minimizing variables well enough to identify statstically relevant trends. I will take into account all suggestions. To address some of them:
-i will review and compare ambient temperature to tank mpg results to see if there is a positive correlation. I'll let you know what i find.
-wife's commute: she takes the same route every day at the same time each day. There is no traffic. Ever. Best commute ever. She drives at to 5mph over. Test track? No, but ya'll are going to have to trust me that it would be hard to create real world driving conditions with fewer variables.
-i have thought about screwing with tire circumference, but have not due to money as well as speedo recalibration issues. In related news, I hope to be installing .681 5th gear in the next few months here.
-re-tune after EGR delete? I don't even know what that is, but i'll look into it.
-fuel volume:i'm aware that the gov allows only minimal inaccuracies in dispensed fuel volumes. I have no way to check this and will have to trust that Uncle Sam is enforcing things.
-Souzafone, i'm newish to the tdi world and did not understand your comment. Would you be so kind to explain what you meant? Thank you!
I invite all others with data to share so we can learn from one another!
Best, Brad
Here's an idea for you to test ..... if the wife is willing? Have her drive 5 mph under the limit instead of over, leaving home 10 minutes or so earlier and enjoy the scenery. I guarantee a significant mpg change.

Second idea.... would your wife enjoy a scanguage 11 ? This would inspire the right foot mod.
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Old March 11th, 2011, 04:22   #15
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Quote:
Originally Posted by AndyBees View Post
keep a skid cover on the bottom of the engine (reduces drag)
Has anyone measured how much impact this makes ? The under cover on my car and the lining of one tire well was ripped off when I got it -- neither are present at all.
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