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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 October 24th, 2010, 22:27   #181
TDI_bubble
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I could see 50mpg being "awesome" at 90mph but that would mean your ALH is inside a velo bike.
Your tank of diesel 2 got you to almost 1,000 miles at 90mph?




I'm calling bull****.
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Old October 25th, 2010, 03:42   #182
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Fuel Economy: 64 .1city @ 30-60 mph/ 52-53 @ 70-85 mph hyway ( 52 to just under 60 normal around town)on LSD
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Originally Posted by TDI_bubble View Post
I could see 50mpg being "awesome" at 90mph but that would mean your ALH is inside a velo bike.
Your tank of diesel 2 got you to almost 1,000 miles at 90mph?




I'm calling bull****.
I have no trouble what so ever getting 50-52 mpgUS @ 70s- low ~80s mph in my 97 Passat TDI tank after tank . I don't see that it would be a lot lower than that if I were able to push it to 90 mph for any length of time . . And I always see low to mid 50s mpgUS in it on city only loops around Denver . Have achieved low 60s mpgUS several times in B4 Passat TDIs and A4 Jetta TDIs on city only loops in Denver and in southeastern coastal NC lower speed only loops .

And I've clocked similar mpgs on higher speed loops under the same conditions in a A4 body ALH engine Jetta TDI . I'm careful about how I drive and I always drive for maximum mpgs . So I have never seen below the mid to high 40s mpgs in any manual trans TDI of any body under any driving conditions @ any speeds .

So under the right conditions if care is taken these numbers are not bullsh!t at all , more than achievable .
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Old October 26th, 2010, 13:30   #183
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71.1 mpg means he really got 59.2 US mpg in a passat since converting from Imperial gal to US gal brings those numbers into something more sensible.

For Hwy driving I have strong doubts as to getting 60 mpg unless level driving is achieved all the time or drafting a semi is done for a considerable amount of time.

As for my commute, about 27-28 miles one way, I travel from ~800 ft to 1000ft, down to 850ft and then back up, and finally down to ~140 ft the latter 40% of my drive. There are 4 areas which I can get about 3.7 miles of coasting without slowing down or minimal enough to be offset with a pulse and glide technique of driving. My best ULSD economy was 57 mpg driving at 55 mph, drafting a semi and pulse+gliding the above. My best repeatable economy is 54-55 mpg doing this route at 55 mph. I'll drop down to 50 mpg if I drive the speed limit of 65. I'm a skeptic of your numbers as well rotarykid because if I apply the same unit conversion of Imperial gal to US gal, your numbers then match mine.
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Old October 26th, 2010, 18:08   #184
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Quote:
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I'm a skeptic of your numbers as well rotarykid because if I apply the same unit conversion of Imperial gal to US gal, your numbers then match mine.
Not sure about Jim Martin's numbers, but rotarykid has been an MPG leader for years, and fully documents his MPG. Just b/c your FE doesn't match his isn't really cause for skepticism. My GF has had two different Jetta ALH's, one a Mark IV 1999, the other a 2003. With similar driving conditions, the older had a "lifetime" average of 45MPG over mixed but mostly hwy driving. The newer one, with almost exactly the same conditions, got 54MPG on it's first trip, and has an average of 52 MPG so far. Same drivers, same roads, same fuels, etc. When I drive her car, I beat my 2003 Golf's FE numbers by 2-3MPG every time. Some cars do better than others, and some drivers can get the most out of their car.
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Old October 26th, 2010, 18:24   #185
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Originally Posted by jim martin View Post
I got 71.1 mpg for 38380mi. with my 2000 Jetti TDI driving like a bat out of hell over mountain passes on the interstate highway system mostly in Colorado and Utah. Advancing the timing was the only alteration to a fully stock 125 hp. TDI. Most of my driving was in excess of 90 mph. I had the timing belt replaced and my car was re-set to factory specs dropping the mpg to 56...have not had the time to re-advance the timing..some trial and error involved.
sorry, but that's impossible. I've owned a bunch of tdi's (1998,2000,2002,2004) and i've never gotten close to that.
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Old October 26th, 2010, 19:43   #186
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Originally Posted by yatzee View Post
sorry, but that's impossible. I've owned a bunch of tdi's (1998,2000,2002,2004) and i've never gotten close to that.
You don't have enough info yet (and neither does anyone else). My mileage goes WAY UP in the mountains. Yours will be much higher too if your willing to exceed the unreasonable posted speed limits. In some cases exceeding 100 moh is easy while idling.
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Old October 26th, 2010, 20:14   #187
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wow, these are all great numbers you guys are hitting! the best I've been able to get out of my 89 jetta diesel with the 1.6n/a is 54mpg. Of course thats keeping it between 55-60mph on the highway.
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Old October 27th, 2010, 07:05   #188
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To get maximum mpgs ;

I use a rolling start out of the garage to start the engine when the engine is cold to avoid battery drain that costs fuel to recharge ,

I skip gears ( 1st , 3rd , 5th most of the time ) and use rpm matching to shift ,

I use "N" when ever possible especially on city loops and when the engine is still cold I kill the engine when coasting in "N" using built up energy to restart when acceleration is required ,

I look down the road to avoid ever if possible over accelerating just to have to brake ,

I install a lot taller than stock tires ( 205-215/75 __" ) along with low mass alloy wheels ( as much as 5"-6" or more taller than stock as much as will fit under the lower end of the shock spring platform without rubbing ) , This not only helps top gear but helps all the gears be taller . If care is taken on take off this one thing can make up to a 5-7+ mpg difference in achieved mpgs over stock tires & wheels . This kills takeoff but that isn't why I drive a diesel anything . This change also can/will under cartain conditions increase stopping distance so you must drive accordingly ........This isn't a modification ( as much as I do it ) that I would suggest to someone without specific driving skills or knowledge . You must know how to realign the suspension to raise the car above factory height as much as I do . A skill which I learned how to do when I drove and worked on race cars when I was young , a skill the average Jo's blow mechanic doesn't have . The extra strain of the taller gearing and advanced timing can/does lead to head gasket failure if pushed !!!

I install an air dam to keep air from getting under the car due the need to raise the car up to fit taller tires ,

And as described above a real biggie in achieving these numbers is the fact that I jack the timing to really early BTDC to maximize energy gotten out of every gallon of fuel .

By themselves most of these things don't add up to a lot of improved mpgs . But when added together these things can add up to a 10-20 overall mpg improvement . A small increase in tire size along with a moderate timing advance can get you an extra 4-7 mpgUS pretty easily . That is as far as most want to go to avoid the blown head gaskets and other modifications required to push things as far as I do . A 3-5 mpgs or more increase can achieved pretty easily with just extra care taken in how you drive ( using the shifting things I've spoke of along with care not to accelerate just to have to hit the brakes ) without changing a thing on the car .
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Old October 28th, 2010, 14:14   #189
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Rotary Kid,

What kind of final drive ratio are you running? How many miles/K rpm?

Planning to use a .622 fifth gear upgrade. Running 185/70x14 tires also.

If you can run it in Colorado, I can run the same gearing in San Diego. Need to look at bumping timing up like you. Hammer mod???

Used to have a 74 RX3 - got it new. Was a real kick to drive. MPG sucked, but that was why I got my 76 Accord - Best MPG was over 47. No kidding. Low 40's were normal.

Best car I ever owned for the first 50K miles. Then I let a dealer do a recall on the car. It turned into a huge POS immediately after that.
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Old October 29th, 2010, 00:22   #190
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I haven't changed any of the internals , just installed taller tires which makes all the gears taller .

I owned a wide variety of Rx's when I was young , 2s , 3s , 4s & the 5 ( Cosmo in the US ) . I even had a R100 for a short period of time in the late 70s . My daily driver in high school was a 74 Rx4 , heavily modified . Man that thing was fast ......I really wish I still had that Rx3sp too , now that was how a sports car should look ..Never cared for the 7s , were just too small for my tastes . That late 80s 7 that had the 13b along with other model only options was a nice one .

With timing , gearing changes , a modified thermal reactor and a lot of care in how they were driven the rotarys could be coaxed into the low 30s mpgUS . With a few mods they would turn 12k+ rpms and push the car past 130 mph too which was fun . I used to eat small block chevys for lunch , the really fun part was showing them what had just blown their doors off .That 12a & 13b were good engines that would take a lot of abuse .
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Old October 29th, 2010, 04:15   #191
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The computer showed only 54 mpg last weekend on the trip back from Waynesboro with a lot of it down the mountain to Charlottesville. Mileage up was 44 mpg. The reprogrammed new module they put in at the 10k service is really showing up.

A Passat is a heavier (just a bit) vehicle than our Jetta.
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Old August 8th, 2012, 09:42   #192
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Sorry I'm late to class... hehe

When I went to a vocational school, the teacher was a retired GM engineer. He told us about the test track speeds for mpg testing. He used to work at the GM track in Arizona or NM (i forgot where it is). Point is, they do many things. No they dont take the back seat out. lol - But, they do get a 105 pound soaking wet driver, use 1.1 gallons of gas and they do drive at 48 miles per hour. This is a small margin below the speed where wind takes effect on the car.

At these speeds a square cube will get 30mpg! Let alone an "aerodynamic" car. In my gas cars I drive by a vacuum gauge and I've noticed that 50 to 55mph is where the wind drag takes effect. I had a Ford van bubble top camper conversion with a 351 V8 that was quite heavy. It got 16mpg at 50 but, by 60 it dropped to 12. Needless to say, I did NOT drive that truck at 70! Wind did have a profound effect on mileage.

If driving a turbo diesel I would install a turbo PSI gauge if you don't already have one and pay close attention to it to see what speed you see a upswing on the pressure curve.

Can anyone find out what speed VW tests these cars on the track? The factory tricks would be very interesting to know
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Old April 11th, 2014, 10:46   #193
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Envy is a harsh mistress.

I envy a harsh mistress...lol

anyways, I just bought a 2014 manual Passat, it's on order from factory, because few people buy the manual.

My 125 kilometre long route to work IS done at 90K, I cannot wait to see the mileage at a forced 90KPH! I expect the fuel consumption to be my guzzling '05 Altima...

It's been 7 weeks waiting for this car, I need it to arrive soon, or else I will get carpal tunnel syndrome for checking my phone for messages from the dealer repeated times.

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Old September 11th, 2014, 09:54   #194
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i just bought a 96 Passat TDi, and it is getting 52MPH highway!
I went on a 900 mile trip on one tank of fuel. WOW am I impressed!
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Old September 11th, 2014, 17:07   #195
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Quote:
Originally Posted by rotarykid View Post
To get maximum mpgs ;

I use a rolling start out of the garage to start the engine when the engine is cold to avoid battery drain that costs fuel to recharge ,

I skip gears ( 1st , 3rd , 5th most of the time ) and use rpm matching to shift ,

I use "N" when ever possible especially on city loops and when the engine is still cold I kill the engine when coasting in "N" using built up energy to restart when acceleration is required ,

I look down the road to avoid ever if possible over accelerating just to have to brake ,

I install a lot taller than stock tires ( 205-215/75 __" ) along with low mass alloy wheels ( as much as 5"-6" or more taller than stock as much as will fit under the lower end of the shock spring platform without rubbing ) , This not only helps top gear but helps all the gears be taller . If care is taken on take off this one thing can make up to a 5-7+ mpg difference in achieved mpgs over stock tires & wheels . This kills takeoff but that isn't why I drive a diesel anything . This change also can/will under cartain conditions increase stopping distance so you must drive accordingly ........This isn't a modification ( as much as I do it ) that I would suggest to someone without specific driving skills or knowledge . You must know how to realign the suspension to raise the car above factory height as much as I do . A skill which I learned how to do when I drove and worked on race cars when I was young , a skill the average Jo's blow mechanic doesn't have . The extra strain of the taller gearing and advanced timing can/does lead to head gasket failure if pushed !!!

I install an air dam to keep air from getting under the car due the need to raise the car up to fit taller tires ,

And as described above a real biggie in achieving these numbers is the fact that I jack the timing to really early BTDC to maximize energy gotten out of every gallon of fuel .

By themselves most of these things don't add up to a lot of improved mpgs . But when added together these things can add up to a 10-20 overall mpg improvement . A small increase in tire size along with a moderate timing advance can get you an extra 4-7 mpgUS pretty easily . That is as far as most want to go to avoid the blown head gaskets and other modifications required to push things as far as I do . A 3-5 mpgs or more increase can achieved pretty easily with just extra care taken in how you drive ( using the shifting things I've spoke of along with care not to accelerate just to have to hit the brakes ) without changing a thing on the car .

Are you taking in to consideration the error in the odometer caused by your taller tire. If not your MPGs is definitely off
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