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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 August 9th, 2013, 23:42   #781
MikeMars
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come on guys, get an Ultra-gage(i have) or a scan-gage(don't have), and get an accurate mile per gallon as u drive ...
The gauges are not necessarily accurate when used in this way. You can only calibrate them at a tank level. For example, my scangauge underestimates the effect of RPM and coolant temperature.
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Old August 10th, 2013, 11:52   #782
roadhard1960
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I have not been keeping up with what tires give the best fuel mileage. There can be huge differences. A friend had a Prius and he lost something significant like 5 mpg. He got it back when he swapped those tires after a few tanks. I use some Michelin Primacy MXV4s. Michelins have worn well and delivered good fuel mileage for me.

For me I tend to drive 65 indicated which is really about 63. Usually far right lane is safe at that speed. I do open windows if it is not too hot or humid. Car is up in the air right now as I discover bad cvjoints. Driving my Cummins only getting 20-22 mpg is killing me. My TDI which is of the better fuel mileage years tends to get 47-50 mpg.
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Old August 10th, 2013, 19:01   #783
deejaaa
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Fuel Economy: 59 latest mpg
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Originally Posted by MikeMars View Post
The gauges are not necessarily accurate when used in this way. You can only calibrate them at a tank level. For example, my scangauge underestimates the effect of RPM and coolant temperature.
using the instant mpg while driving informs the driver what is affecting the overall mpg. ie: cruising 70 behind a semi, road conditions (concrete, asphalt), head/tail winds, diff speeds. it doesn't have to be accurate (because mileage should be figured with pen and paper) but allows better use of fuel when you pay attention to it and adjust to the conditions. that's how i got 58.8 on my last fill up.
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Old September 7th, 2013, 22:04   #784
gary9696
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Fuel Economy: 38.9/45 - 54
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Originally Posted by rotarykid View Post
The grill opening is closed for several reasons, a closed grill vent gives Longer filter life, gives some Engine noise reduction and lowers Emissions output ( less cold fresh air gives lower NOx ).

This engine was detuned for the US market to pass emissions so really doesn't require the vent be opened to give stated output rated power.

First, a closed vent helps in keeping the air filter clean longer increasing the rated filter life time and mileage rating range. Diesel engines suck in large volumes of air compared to their gasoline counterparts, many times that of their gasoline counterparts. So it can clog up quickly in adverse conditions. A closed front air ram vent can keep this from happening sooner in the filter life. Americans are notorious for ignoring maintenance so a long filter life was a must for the US market.

Second, a closed vent lowers overall engine noise from in front of the car, cars have a maximum allowed noise limit. VWofA has been using this trick here in the US/Canada for decades on diesel powered models to lower engine noise. VWofA figured diesels were a hard sell outside of the VW diesel die-hard market. So to increase sales numbers here to include other than the diehard diesel market the vent was closed. For VWofA to consider bringing a diesel powered model to the US market it must have wider sales appeal which the closing of this vent gave.

Third and likely the main reason the duct was closed was that fresh cold air increases from a open air duct is denser. Denser air gives more power from more complete combustion which leads to higher N0x levels. This car was really close to N0x limit and a open grill more than likely caused the car to fail emissions. Closing the vent lowered power( the engine was already detuned for the US market to pass emisions ) and it lowered N0x emissions to help pass our stupid emissions rules.

You will see better throttle response at speed with the duct open and you will see higher mpgs. But N0x emissions will be significantly higher and air filter life will be shorter if you are exposed to dirty or wet conditions.

I made this modification to a friends 04 Passat TDI a while back and he clocked a 3-5 mpg increase also, biggest increase in mpgs was on the highway at higher speeds. The car is however now louder if you are standing right in front of the opening while running.

A precaution that must be taken into consideration is that you must keep closer tabs on the air filter cleanliness. A look-see air filter and air box inspection ever so often will be a must once this mod is made. Once this change is made if you drive through dusty conditions or in very wet conditions you must inspect the filter for damage or clogging issues regularly.

Are there any other VW TDI vehicles with this ram air vent closed?

Last edited by gary9696; September 7th, 2013 at 22:05. Reason: needed to add the word vent
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Old September 7th, 2013, 22:17   #785
Baumeister
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Originally Posted by gary9696 View Post
Are there any other VW TDI vehicles with this ram air vent closed?
my 2004 Passat 1.8t gasser has it closed...haven't compared it to the TDI version to see if it's any different.
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Old September 8th, 2013, 19:54   #786
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So i have a 2013 Jetta TDI, automatic.

I got my best mpg this last fill up at 45.8 but I do use cruise control as I have a 40 Mile straight run on highway from home to my job. I set it to 65 and usually never have to hit the break.

I am doing some reading in this thread and I am a bit confused. The trip is quite hilly as I head down 78 from NJ to PA. Some hills are steep and I notice that the average MPG for the trip go down quite a bit as I go up and as I head downhill the MPG for the trip go back up. By the time I get to work the trip estimator for MPG is usually 49-50. (the estimator is always wrong tho as when I fill up the tank its usually just over 3 miles off from the actual mpg for the fill up).

I have done the trip several times without using CC and I can still get the mpg to estimate at 49. But I notice when I go up the hill it shows the current estimated mpg goes down way more then when I use CC. My speed also seems to slow down going up the hill and the mpg stays low as I try to get back to 65.

Any pointers on how I can improve or is CC the best option for me?
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Old September 9th, 2013, 10:43   #787
Jagerbecher
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Originally Posted by thomamon View Post
I have done the trip several times without using CC and I can still get the mpg to estimate at 49. But I notice when I go up the hill it shows the current estimated mpg goes down way more then when I use CC. My speed also seems to slow down going up the hill and the mpg stays low as I try to get back to 65.

Any pointers on how I can improve or is CC the best option for me?
Sounds like when yo do not use CC you do not work with your accelerator pedal good enough to keep the speed at 65 when the road starts going up and your car loose momentum. Then you try to get back to 65 already going up hill and that requires more fuel then if the CC just maintains the speed at 65. If it's a long incline i would say CC it's better to use CC. Also, you can have the CC set at 65 all the time and just accelerate with the pedal on downhill or level sections to gain more momentum "for cheap" before next hill.
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Old September 9th, 2013, 15:27   #788
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Originally Posted by Jagerbecher View Post
Sounds like when yo do not use CC you do not work with your accelerator pedal good enough to keep the speed at 65 when the road starts going up and your car loose momentum. Then you try to get back to 65 already going up hill and that requires more fuel then if the CC just maintains the speed at 65. If it's a long incline i would say CC it's better to use CC. Also, you can have the CC set at 65 all the time and just accelerate with the pedal on downhill or level sections to gain more momentum "for cheap" before next hill.
So as I am about to approach downhill, even when using CC I should increase my speed? How much?

I would say its safe to assume going up hill I am not the best, yet...
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Old September 9th, 2013, 18:31   #789
gary9696
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Quote:
Originally Posted by thomamon View Post
So i have a 2013 Jetta TDI, automatic.

I got my best mpg this last fill up at 45.8 but I do use cruise control as I have a 40 Mile straight run on highway from home to my job. I set it to 65 and usually never have to hit the break.

I am doing some reading in this thread and I am a bit confused. The trip is quite hilly as I head down 78 from NJ to PA. Some hills are steep and I notice that the average MPG for the trip go down quite a bit as I go up and as I head downhill the MPG for the trip go back up. By the time I get to work the trip estimator for MPG is usually 49-50. (the estimator is always wrong tho as when I fill up the tank its usually just over 3 miles off from the actual mpg for the fill up).

I have done the trip several times without using CC and I can still get the mpg to estimate at 49. But I notice when I go up the hill it shows the current estimated mpg goes down way more then when I use CC. My speed also seems to slow down going up the hill and the mpg stays low as I try to get back to 65.

Any pointers on how I can improve or is CC the best option for me?
If you have the DSG have you tried pushing the gearshift to the right from D to keep it in 6th gear. I have noticed on the highway that when going uphill with it in 6th gear not in D that it doesn't increase speed, and lets the car drop speed a little, then on the way down the hill the mpg increases with it in that 6th gear. Of course though this depends on how steep your hill is on the downside as to how much the mpg will increase.
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Old September 9th, 2013, 18:37   #790
thomamon
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Originally Posted by gary9696 View Post
If you have the DSG have you tried pushing the gearshift to the right from D to keep it in 6th gear. I have noticed on the highway that when going uphill with it in 6th gear not in D that it doesn't increase speed, and lets the car drop speed a little, then on the way down the hill the mpg increases with it in that 6th gear. Of course though this depends on how steep your hill is on the downside as to how much the mpg will increase.
I have not tried that...

When I go up the hill it seems to decrease speed, not increase. Is that what you meant? If not what exactly should I try?
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Old September 9th, 2013, 19:52   #791
gary9696
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Originally Posted by WestyConvert View Post
I'm getting REALLY poor fuel econonmy on my 2006, Jetta Wagon TDI (8 L/100 km or about 29 US MPG - all city driving). Just wanted to see if anyone out there had any suggestions as to why this might be and how I can get improve my economy.

Help!
What is the curb weight of your vehicle considering you added a cast iron diesel engine to a VW Vanagon? What was the mpg with the gasoline engine before you or someone did the TDI conversion?
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Old September 9th, 2013, 20:29   #792
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Is my mpg good, or at least above average for my 2013 JSW DSG TDI 38 city, 45 - 54 (depending on hills) highway? My factory air intake near the front of the hood has a fresh air opening in the front, and engine compartment air opening on the back. Has anyone tried blocking the rear intake to find out if getting more fresh air, and closer to a ram effect helps increase the mpg?
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Old September 9th, 2013, 22:00   #793
Jagerbecher
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Originally Posted by thomamon View Post
So as I am about to approach downhill, even when using CC I should increase my speed? How much?

I would say its safe to assume going up hill I am not the best, yet...
I meant increase the speed on flat sections or downhill sections before the next hill regardless of whether you are using CC or not, but for long grades I think it makes more sense to use CC since it keeps the car in constat speed and it does not loose momentum.

Look at the post #147 and #148 in this thread http://forums.tdiclub.com/showthread...335035&page=10
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Old September 10th, 2013, 10:09   #794
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Lots of great info on this site. I am a Newbie to this Site I just picked up my 1st TDi a month ago. (2002 beetle 90,000 really good shape) I have been reading through post for tha last couple week. My goal right now is to get to 50 MPG. my 1st 2 tanks - 44 and 46.5. I just ordered a Ultra-Gauge. I drive almost 45 miles a day. thanks for all of the helpful information.
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Old September 13th, 2013, 00:13   #795
gary9696
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Quote:
Originally Posted by WestyConvert View Post
I'm getting REALLY poor fuel econonmy on my 2006, Jetta Wagon TDI (8 L/100 km or about 29 US MPG - all city driving). Just wanted to see if anyone out there had any suggestions as to why this might be and how I can get improve my economy.

Help!
Sorry somehow I thought you were talking about your mpg on the converted Vanagon.
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