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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 May 31st, 2017, 14:02   #916
JohnWilder
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Quote:
Originally Posted by 2rob View Post
I also have an 05 Passat wagon. Most of my driving is above 6,000' so less o2, less fuel, less power, better mileage. Was in Portland last month and mileage dropped into the 30's on the highway. Is that what you get with your 05 ? I do the driving techniques. Tried a cheap chip and got no improvement either 0-60 mph or mileage.
Any thoughts would be appreciated.
Rob
Driving at high altitude results in less drag so less power needed. I've noticed a measurable improvement at high altitude in mileage. However your engine will produce sea level power at 6000 ft. if necessary. It is turbocharged.
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Old May 31st, 2017, 14:06   #917
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Driving at high altitude results in less drag so less power needed. I've noticed a measurable improvement at high altitude in mileage. However your engine will produce sea level power at 6000 ft. if necessary. It is turbocharged.
Isn't that offset by the thinner air at height? I spent a short time in the Rockies and my mileage never seemed to creep past about 42 mpg, whereas "at home" in the deep south it was usually 45-49 mpg. The tank of fuel used going from Dallas to Arizona didn't even hit 39.
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Old May 31st, 2017, 14:07   #918
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and p.s.
Has anyone found the way to time those dang stop signs? It seems like no matter how far back i start slowing, they are always red when i get to them. [/QUOTE]
I also live in Texas. I consider the designs of Texas roads to some of the worst I've seen. The parallel frontage roads on limited access highways is awful. I can't imagine who came up with such nonsense. I know they can time lights. How do I know? Because you will hit every red light no matter how you drive. Welcome to Texas! I believe it is deliberate to try to get you onto the toll roads. They make driving as aggravating as possible if you wish not to pay the toll.
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Old May 31st, 2017, 14:14   #919
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I'm not 100% certain, but here is my theory: In the U.S., it is typically illegal to coast in neutral.

Although this law is probably intended to apply to manuals, the law probably doesn't specify.

As such, auto manufacturers are either legally required to sell auto-equipped cars which coast in gear, or face litigation every-time one gets into an accident.
These laws are from the old days of drum brakes that faded with excessive use. I've never heard of any such low being enforced in the last 30 years. Furthermore how would they know if you were coasting?
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Old May 31st, 2017, 14:15   #920
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I'm somewhat dubious that shortened oil-change-intervals would lead to meaningfully better MPG.
I agree. I'd like to see the data.
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Old June 6th, 2017, 15:19   #921
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Originally Posted by Tom Servo View Post
Isn't that offset by the thinner air at height? I spent a short time in the Rockies and my mileage never seemed to creep past about 42 mpg, whereas "at home" in the deep south it was usually 45-49 mpg. The tank of fuel used going from Dallas to Arizona didn't even hit 39.
My point is that drag is lower at any given speed at altitude due to the lower density of the air. If there is less drag then less power is required to move the car at any given speed. Why your mileage changes I don't know. I do know if you drive is a way to minimize the use of your brakes you will notice higher fuel economy. Remember every btu of heat generated in the brakes originally came from the fuel that did not move the car.
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Old June 23rd, 2017, 17:30   #922
New Mickey
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Quote:
Originally Posted by Tom Servo View Post
Isn't that offset by the thinner air at height? I spent a short time in the Rockies and my mileage never seemed to creep past about 42 mpg, whereas "at home" in the deep south it was usually 45-49 mpg. The tank of fuel used going from Dallas to Arizona didn't even hit 39.
A naturally aspirated engine loses power as altitude increases. Turbocharging can maintain sea level intake pressures up to a certain critical altitude. (Said to be 6000 feet in the case of the TDI.) Altitude has no effect on power up to the critical altitude, but the car IS moving through thinner air. It won't matter at slower speeds, but at freeway speeds it becomes a substantial issue.

So in town it won't matter, but on the freeway at high speeds it will. The higher the speed the greater the effect of aerodynamic drag....and it's not a linear relationship. Drag increases exponentially as speed increases. Very little difference between 25 and 30 mph, but BIG difference between 75 and 80 mph, for example.

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Old June 23rd, 2017, 17:36   #923
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re: "Coasting in neutral." There is no such law. If anything it has to do with the way transmissions work. If the clutch is engaged and the transmission is in neutral then the input shaft of the transmission is loping along at "idle" speed while the output is spinning furiously.

It's also true that you have somewhat less control in neutral. The car will accelerate downhill more quickly than if the transmission is engaged, and you don't have engine braking to help you if you need to slow down quickly. Stopping distances are increases somewhat.

-mickey
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Old June 23rd, 2017, 17:44   #924
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So here's a little bit of a trick.

"Hypermiling" involves working with gravity rather than against it. Allow the car to accelerate downhill, and let the speed bleed off going uphill. It make a huge difference, but may get you SHOT in traffic.

But that mindset can help you save some fuel if you have a DSG. When going downhill with the cruise control set the transmission will shift down a notch to help you slow down. Bump the stick into Tiptronic mode and it'll stay in top gear. You'll gain a bit more speed, which pays off as you get back on the flat.

If conditions warrant you can practice more aggressive hypermiling. The ultimate goal would be to maintain a constant power output. Whatever would keep you moving at a given speed IF THE ROAD WERE FLAT. Hold that power, and let the hills do what they will. Slow down going uphill, and speed up going downhill.

Other than that, I guess it's a question of how you define "economy." Are you talking about fuel or money? There at a lot of little things you can do to maximize FUEL economy, but most of them cost more than they're worth. If saving MONEY is the goal concentrate on driving style, avoiding carrying unnecessary weight in the car, and keep the tires properly inflated. (Don't be tempted to overinflate them in the name of "fuel economy." Any fuel you save is more than offset by the tires you ruin.....and tires are made of OIL, mostly.)

-mickey
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Old June 23rd, 2017, 17:48   #925
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Watch your A/C. If you must use it, run it in Recirculate mode. You're only cooling the already cool interior that way, rather than trying to solve global warming.

If the outside air temperature is acceptable switch off the A/C. Use a higher fan setting, or crack the windows. That'll cause a LOT less drag than running the A/C compressor.

A/C running on a hot day can make a couple MPGs difference with a tiny engine and a lightweight car. I never noticed any difference with my full-size 4x4 pickup because everything is relative, and the A/C's drag was lost in the overall "hauling around 5000 pounds of metal".

-mickey
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Old July 10th, 2017, 13:00   #926
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I recently donated my 2002 Jetta TDI w/283,000 miles manual transmission. The car ran great and recently went into limp mode once. Hence, I gave it away. Consistently got 48-50+ mpg on the HWY. Usually drive 65 MPH in a 55 zone, 72 MPH in a 65 zone, and 80 MPH in a 75 zone. AC usage depending on weather. I drove the car from Philly to Denver end of Sep 2016.

Have 2006 (05.5) TDI DSG now. Went to Philly in June and came back to Denver two weeks later. Best I got was 40.8 mpg!! Tire pressure at 36 psi. Clean air filter. No clogs. Fuel filter new. Timing belt new. One highway segment (80 MPH, AC on, cruise on) gave only 36 mpg. What else should I check into? SCarroll doesn't participate much in these forums. One experience with A....ee not positive. Is there any other guru in and around Denver?

I wish I hadn't parted with my 02 TDI!

Chitti
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Old July 10th, 2017, 13:22   #927
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The 2006's Seemed to be sensitive to where the timing was set to. +/- a little each way seemed to make a big difference in economy. There was/is a thread here about this.
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Old July 13th, 2017, 07:32   #928
Chitti
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Originally Posted by Lightflyer1 View Post
The 2006's Seemed to be sensitive to where the timing was set to. +/- a little each way seemed to make a big difference in economy. There was/is a thread here about this.
Thank you. Still searching for a good TDI guru in CO to look at the timing belt install.

Thanks again,

Chitti.
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Old July 13th, 2017, 07:45   #929
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There are 4 in the Denver area on the trusted mechanics list.
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Old July 13th, 2017, 14:19   #930
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Quote:
Originally Posted by Chitti View Post
I recently donated my 2002 Jetta TDI w/283,000 miles manual transmission. The car ran great and recently went into limp mode once. Hence, I gave it away. Consistently got 48-50+ mpg on the HWY. Usually drive 65 MPH in a 55 zone, 72 MPH in a 65 zone, and 80 MPH in a 75 zone. AC usage depending on weather. I drove the car from Philly to Denver end of Sep 2016.

Have 2006 (05.5) TDI DSG now. Went to Philly in June and came back to Denver two weeks later. Best I got was 40.8 mpg!! Tire pressure at 36 psi. Clean air filter. No clogs. Fuel filter new. Timing belt new. One highway segment (80 MPH, AC on, cruise on) gave only 36 mpg. What else should I check into? SCarroll doesn't participate much in these forums. One experience with A....ee not positive. Is there any other guru in and around Denver?

I wish I hadn't parted with my 02 TDI!

Chitti
The PD engines are just not as fuel efficient as the the rotary type injection engine.

You can tweak the timing some on the PD engine and increase the fuel efficiency. But it will never be as fuel efficient as the ALH or 1Z engines. Using high gear and keeping speeds down are the primary ways to increase fuel efficiency on the PD engine.

Also using coasting techniques with use of N when possible will help. Your numbers are actually pretty good for a PD engine on a drive like that.

On alh engines going into safe mode like you described you likely had a clog intake or head which was causing an over pressure to appear to be over pressuring the boost going into the engine. This is a common issue on these cars.
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