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I just bought a 2001 VW Jetat TDI and was wondering if the cold weather plays a part in getting the full miles per gallon as stated on the manufacturers list of features. It states that the TDI should get 49 mpg highway and I am barely getting 30mpg. Is there something to do to the fuel or how you drive the car? Thanks!
 

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What it does to milage I don't know... I do know that it makes it hell to start my truck in the morning.
 

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I am not sure, but I think the cold would help rather then harm fuel mileage, since it is turbocharged. Since it is colder outside, the air is more dense per square foot, thereby increasing engine efficency and hence, mileage.

The other end, though, is that since it is a diesel, and thereby must rely on glow plugs to warm up the engine during cold starts. Since the engine will not be operating in its peak range for an extended period due to the cold weather and the amount of time it will take to warm up, that could be one reason.

If the mileage doesn't improve, I would definitely take it back to the dealer and see if there isn't something wrong with it. Although if it is brand new, it may still be going through the engine's break-in period, where there is extra friction within the cyclinders, decreasing fuel economy (although not by the amounts you've described.)

Overall concensus =
 

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Also, I think that the factory quotes their mileage with the assumption that the engine won't rev much at all. This is becuase it is a diesel and has ample torque low in the powerband, also because diesels don't like to be rev'ed much because of the high compression ratio (and hence long stroke = not very revable.) hope this helps...
 

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<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by 109 LUVR:
Also, I think that the factory quotes their mileage with the assumption that the engine won't rev much at all. This is becuase it is a diesel and has ample torque low in the powerband, also because diesels don't like to be rev'ed much because of the high compression ratio (and hence long stroke = not very revable.) hope this helps...
<HR></BLOCKQUOTE>

This is also true, remember what was said about the shifting Trish, they claimed for best mpg to shift around 2500 rpm. Crappy I know, but I'm not sure this is the only problem. I am leaning towards looking into problems with the EGR, air filter, fuel filter, air box snorkel being clogged, or possibly even fuel quality. You have an apointment tommorrow, so we will see what they say, worst case theres always the 30-day option


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Discussion Starter #6
where do you get those pictures!?! thank you!
 

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<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by 109 LUVR:
I am not sure, but I think the cold would help rather then harm fuel mileage, since it is turbocharged. Since it is colder outside, the air is more dense per square foot, thereby increasing engine efficency and hence, mileage.

The other end, though, is that since it is a diesel, and thereby must rely on glow plugs to warm up the engine during cold starts. Since the engine will not be operating in its peak range for an extended period due to the cold weather and the amount of time it will take to warm up, that could be one reason.

If the mileage doesn't improve, I would definitely take it back to the dealer and see if there isn't something wrong with it. Although if it is brand new, it may still be going through the engine's break-in period, where there is extra friction within the cyclinders, decreasing fuel economy (although not by the amounts you've described.)

Overall concensus =
<HR></BLOCKQUOTE>

I know my mileage is better in the summer. I assume it is because I don't have to let the car warm up and it spends more time running at a more optimal operating temp. I'm not so sure having the more dense air/fuel mixture would make it more fuel economical but rather less b/c it means more fuel is in there. You are obviously right about the more power thing though. I'm not so sure about the fuel economy aspects of the cold weather though.
 

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i've noticed a significant drop in my milage... it wasn't this bad last winter, but it wasn't this cold either. i've tried to think of reasons why my milage is going down, but i can't think of any real good reasons... only the fact that i have to warm up my car for a good while before i drive it... but who really knows

[ January 26, 2004: Message edited by: obsessedubber ]
 

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<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by Tommunist:
I know my mileage is better in the summer. I assume it is because I don't have to let the car warm up and it spends more time running at a more optimal operating temp. I'm not so sure having the more dense air/fuel mixture would make it more fuel economical but rather less b/c it means more fuel is in there. You are obviously right about the more power thing though. I'm not so sure about the fuel economy aspects of the cold weather though.<HR></BLOCKQUOTE>

True, more air in the cylinder would require more fuel, but only slightly more. The key idea to keep in mind is that while you may be using slightly more fuel per combustion cycle, you are getting more power out of each powerstroke, and therefore the engine does not need to be rev as much, thereby saving gas since the engine is injecting fuel into the cylinder fewer times over a given period of time.

I could attempt to create an example, but I just got out of my Statics class and feel like having nothing to do with Academia for a few hours...
 

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I'd ask the dealership about that, when I got my car I was getting 29-32MPG on the highway with a VR6, not I get 27-29 usually. I tend to drive at higher RPM's now though, I keep it in 4th at higher speeds than I used to.
 

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The TDI is actually a very good diesel for the winter. VW has em starting at temps well below 0F. As for fuel economy, it should be better in the winter due to the colder air, which leads to better volumetric efficiency. Ever wonder why gas prices go up in the summer? Everyone is driving around...gas mileage can go down due to many factors (electrical usage, A/C, etc) and due to the fact the air is warmer.

To wring every mile out of your TDI's claimed fuel economy, shift early and not for power. Keeping the RPMs low draws less fuel. You also can get away with it due to the TDI's massive torque. Also, fill up at a reputable diesel station, and make sure to add some anti-gelling agent to every fill-up. You can obtain the factory recommended anti-gel at your local dealer. Gelled diesel fuel can not only hinder your fuel economy, it can also cause your engine to stall or not start. With the low temperatures, its important to make sure your diesel fuel is ok.
 

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How fast you drive will also affect your fuel usage. (i'm not just talking about shifting at lower RPM's either.) If you are at higher speeds for longer then it will hinder the mileage, because i would assume (and yes i could be an @$$ for doing so but) that the highway MPG's would be taken at an average of about 55 mph... considering that's most speed limits on highways. I mean i travel highways morning and night and do between 65-75 MPH most of the time and i'm getting between 25-30 MPG in my GTI 1.8t. But you shouldn't be losing that many MPG's unless there are other issues. depending on the mileage and this weather the fuel filter may be clogging (from jelled diesel)and it's not coming through as clean so it's burning crappy fuel. Either way all i'm saying is that there is most likely other issues besides cold wether.
 

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<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by GTIVR62801:
To wring every mile out of your TDI's claimed fuel economy, shift early and not for power.<HR></BLOCKQUOTE>

In other words, drive like a grandma!



oh and congrats on your new dub Patty!

[ January 29, 2004: Message edited by: silverGTI ]
 
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