Temps really affect mileage.....

amafrank

Well-known member
Joined
Feb 17, 2009
Location
USA
TDI
'06 TDi jetta, '09 TDi jetta wagon, 15 TDi GSw
now that we're finally over 50 deg here in Indiana the mileage in the GSW has finally climbed above 40mpg real and 43mpg according to the dash. Last fillup showed 45mpg dash and turned out to be 41.8 real. This is the first time I've gotten better than 40mpg out of this car since december when I got it. Yesterday with the temps in the 70s I averaged over 49mpg according to the dash on a trip of 120 miles of varied town and country road driving which is shocking to me. Why the difference with temps?

My 2006 Jetta Tdi sedan averaged over 41mpg for its whole 200K mile life regardless of outside temps. I didn't get better mileage in the summer than I did in winter. I got better mileage on long trips and when I kept my foot off the pedal. It did over 50mpg when I did a lot of interstate driving without flooring it. 45mpg was normal for the road, temps didn't matter. The 2009 Jetta Tdi Sportwagen is the same. No difference summer to winter.... What is the reason behind this? Seems counter intuitive when colder air is denser and keeps combustion temps a bit lower along with better air density in the cylinder. Should be better mileage in winter?


Frank
 
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This_Fuggin_Guy

Active member
Joined
Apr 26, 2017
Location
New Jersey
TDI
2015 GSW
I was getting 39-43 mpg all winter long, mostly on the lower side of that spectrum. When I filled up a week ago, I got 48 mpg and on this tank, with temps over 60 every day, I'm on track for over 50 mpg. These are all calculated numbers, not what the dash says. All last summer I was getting 50-53 mpg consistently.

I really don't like how much my mileage fluctuates depending on the weather. This is my first diesel so I'm still learning how these engines run.
 

The Tortoise

Veteran Member
Joined
Apr 24, 2017
Location
Ottawa
TDI
2015 GSW Trendline - White
Correct me if I am wrong, but don't all cars suffer similar economy losses in the winter?

If the diesel takes a bigger hit, it's likely due to the longer warm up time for the emissions components to get to operating temps. And there's always the winter blend for the diesel fuel.
 

pdq import repair

Veteran Member
Joined
Nov 6, 2016
Location
idaho
TDI
09 Jetta
Fuels change for the winter, both diesel and gas, which affects mileage somewhat. I think diesel owners notice it more because we are always bragging about how good it is and become crybabies when it drops 1 MPG.

I installed an auxiliary heater on my car that helps the engine, and the heater, warm up faster. I noticed that when I ran it this winter the mileage was better than when I didn't, so engine temp does make a difference.
 

This_Fuggin_Guy

Active member
Joined
Apr 26, 2017
Location
New Jersey
TDI
2015 GSW
Correct me if I am wrong, but don't all cars suffer similar economy losses in the winter?

If the diesel takes a bigger hit, it's likely due to the longer warm up time for the emissions components to get to operating temps. And there's always the winter blend for the diesel fuel.
Yeah, I've always notice a decrease in mpg between summer and winter in all my gas cars but at most 3-5 mpg not the 7-10+ mpg decrease I have noticed in my TDI.
 

Rico567

Top Post Dawg
Joined
Jun 13, 2003
Location
Central IL
TDI
2013 Passat TDI SEL Premium (Turned in 7/7/18)
The combination of the cold weather and the D1 mixed with the D2 for the winter fuel is going to be noticeable, nothing that can be done about it. And don't forget colder air is denser, so it's harder to push through.
In gas cars, winter brings the cheaper, more volatile fractions into the fuel, because they don't evaporate as badly. Summer gas is a higher quality fuel. Again, these things are the same for everybody.

NB: You can do yourself a favor with diesel by putting on a set of winter fronts in the cold weather. I use the ID Parts product, and really like it.
 

740GLE

Top Post Dawg
Joined
Aug 19, 2009
Location
NH
TDI
2015 Passat SEL, 2017 Alltrack SE; BB 2010 Sedan Man; 2012 Passat,
Just be aware that W2A intercooler keeps that heat waayyy longer than it should if you are pushing the car to the limits (hardly many do). I saw 330F charged air cooler temp during a regen on our Passat and it took a little while for temps to fall back to normal. Typical crusing temps were 20-30F higher than coolant of 195-199 (outside temps were 80-90).
 

ssffnomad

Veteran Member
Joined
May 18, 2014
Location
Upstate N.Y.
TDI
2015, GSW, S, TDI, 6MT. 5/2017
Our friends at I.D. Parts are going to have a Winter Cover for us MK7 guys before next Winter
 

amafrank

Well-known member
Joined
Feb 17, 2009
Location
USA
TDI
'06 TDi jetta, '09 TDi jetta wagon, 15 TDi GSw
I never noticed any difference summer to winter in my Ford F350/powerstroke diesel or the 2006 and 2009 VW diesels. I also never noted any difference due to temps in any of the gasoline powered cars I've owned in the last 40 years. I've been tracking mileage since I was a kid.....corrupted by my dad. I could see small variations due to different fuel for winter or summer but not what I'm seeing here.
My guess is that the earlier diesels weren't really pushing the limits of fuel economy and power like the newer ones. Maybe with the current generation they are making more power through more electronic enhancement so the little details like wax inhibitors and summer vs winter fuel create more of an issue.
Don't really know......

Frank
 

mvoss15

Well-known member
Joined
Jul 31, 2005
Location
Indiana
TDI
2014 Audi Q7 TDI, 2015 Golf Sportwagen TDI (previous 05 Jetta TDI, 09 JSW TDI, 05 Jeep Liberty CRD)
Hey Frank - where in Indiana are you? I don't see too many 15 GSW TDI's on the road around here!
 

amafrank

Well-known member
Joined
Feb 17, 2009
Location
USA
TDI
'06 TDi jetta, '09 TDi jetta wagon, 15 TDi GSw
East central indiana.....just west of Richmond. I see a few but not a lot of Tdi's. I had to go to Clarksville to find mine.

Frank
 

mvoss15

Well-known member
Joined
Jul 31, 2005
Location
Indiana
TDI
2014 Audi Q7 TDI, 2015 Golf Sportwagen TDI (previous 05 Jetta TDI, 09 JSW TDI, 05 Jeep Liberty CRD)
Cool! I'm up in Marion. Have any recommendations for a good TDI mechanic in the area? Just moved back to IN from New Jersey, and haven't found anyone around here yet.
 

Blue_Hen_TDI

Top Post Dawg
Joined
Oct 23, 2005
Location
Slower, DE
TDI
owned: 96 B4V, 06 Golf, 12 NMS, 15 GSW
Cold temps certainly affect mpg. I actually had one tank below 50 mpg in January (49.71 mpg) when we were getting down in the single digit temps. That sucked.

Warm temps plus a nice tail wind on the commute home:

 

amafrank

Well-known member
Joined
Feb 17, 2009
Location
USA
TDI
'06 TDi jetta, '09 TDi jetta wagon, 15 TDi GSw
Cool! I'm up in Marion. Have any recommendations for a good TDI mechanic in the area? Just moved back to IN from New Jersey, and haven't found anyone around here yet.

Right now I'm using VW of Muncie. There is still warranty left on this one so I have to deal with the dealer for a bit. Otherwise we've been taking the TDi's to Dargies in Richmond. Neither of which are really close to Marion....

Frank
 

wesintl

Member
Joined
Dec 19, 2002
Location
Colorado
TDI
02 jetta tdi
I actually miss the mileage of my 02 alh jetta. The GSW is more fun but the dsg, winter, and altitude kill my mileage
 
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