Cold Weather MPG Losses

Right Lane

Active member
Joined
Oct 23, 2012
Location
New England
TDI
2013 Golf
I've got about 4500 miles on my 2013 Golf TDI with DSG. I understand that there will be cold-induced parasitic losses to my mpg but I'm experiencing greater losses than expected. I commute the same route daily - about 70-miles round trip through stop-and-go to 65 mph. I use Shell fuel only from one of two stations who discount steeply (ensuring supply turnover). I have the factory Continentals that are set cold at an accurate 40 psi at an ambient outside temperature of 28F. Accessory load is the same from day to day. My measured mpg calculated at fill-up has varied from just over 36 mpg to just over 42 mpg. Now the problem: The MFI average seems to be pretty accurate and I will check it at the same point into my daily commute (this is during the morning portion of my commute and 90% of this is with the cruise control set). When the local temperature spiked to 60F last week, the MFI indicated 48.0 mpg at my check point; however, at 8 or 10F I'm looking at less the 30 mpg at the same check point. I realize that the atmosphere is more difficult to punch through at colder temps but for the life of me, I'm at a loss to explain this much of a discrepancy. Others must be going through this too and I'm wondering if something is going on in the combustion process that I'm missing?
 

Spanish Key

Veteran Member
Joined
Nov 24, 2012
Location
CNY/ADKS
TDI
2013 Jetta 6M
We're in a similar situation with similar cars in a similar climate and terrain and similar mileage on the clock, though I have the 6 sp. I've found that the hit varies, but is generally around 5 mpg. Factor in the reality that every trip--even over the identical route--is going to vary depending on traffic patterns, wind speed and direction, road condition (snow, ice, etc. add rolling resistance), and you see that sometimes you eat the bear; sometimes the bear eats you.

My FE is just a little better than yours over the life of my car so far. I expect that to rise once we get into warmer temps and better fuel to the 45 mpg+ range. Give me a little more practice squeezing mileage and let the engine break in, and maybe it will be closer to 50.

Considering this engine feels and acts like a V8, I'm pretty happy with the numbers I'm getting.
 

MikeMars

Veteran Member
Joined
Mar 6, 2008
Location
UK
TDI
Vento 1.9 TDi (retired), A4 1.9 TDi (rear end collision), VW Passat 1.9 TDi (retired), Audi A2 1.4 TDi
Your figures seem reasonable to me. Cold engines always have much worse fuel consumption than warm. It might be worth investing in a block heater to keep your engine warm in winter?
 

psd1

Veteran Member
Joined
Aug 4, 2011
Location
OR
TDI
2006 Jetta 2013 Passat SE 6Man
I've got about 4500 miles on my 2013 Golf TDI with DSG. I understand that there will be cold-induced parasitic losses to my mpg but I'm experiencing greater losses than expected. I commute the same route daily - about 70-miles round trip through stop-and-go to 65 mph. I use Shell fuel only from one of two stations who discount steeply (ensuring supply turnover). I have the factory Continentals that are set cold at an accurate 40 psi at an ambient outside temperature of 28F. Accessory load is the same from day to day. My measured mpg calculated at fill-up has varied from just over 36 mpg to just over 42 mpg. Now the problem: The MFI average seems to be pretty accurate and I will check it at the same point into my daily commute (this is during the morning portion of my commute and 90% of this is with the cruise control set). When the local temperature spiked to 60F last week, the MFI indicated 48.0 mpg at my check point; however, at 8 or 10F I'm looking at less the 30 mpg at the same check point. I realize that the atmosphere is more difficult to punch through at colder temps but for the life of me, I'm at a loss to explain this much of a discrepancy. Others must be going through this too and I'm wondering if something is going on in the combustion process that I'm missing?
Nothing to see here folks, please move along!;)

100% normal! Check some fuelly accts and look at the differences on economy from the summer months to the winter months.
 

VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
Jul 2, 2000
Location
La Conner, WA
TDI
2018 Tesla Model 3: 217,000 miles
Three words: Electric Cabin Heater.

This 1500 watt electric element puts a massive load on your alternator (in combination with glow plugs, heated seats, rear defrost, and whatever else you happen to be running), thus consuming significantly more fuel than in the summer. It's either that or freeze your ass off until the engine fully warms up (if you prefer this option, turn your HVAC off).

I haven't nailed down the specific algorithm that the car uses for determine when to run the electric heater - yet. Initial research shows that it will run any time the coolant temp is under 170F and the HVAC is calling for heat. Also, I have only checked the Climatronic system, so I have no idea how it actually functions on the manual climate control system. Quick check: if your engine is doing a fast idle (~950 RPM), it is probably running the electric cabin heater - VCDS shows the HVAC system calling for engine fast idle.
 
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Right Lane

Active member
Joined
Oct 23, 2012
Location
New England
TDI
2013 Golf
I've got about 4500 miles on my 2013 Golf TDI with DSG. I understand that there will be cold-induced parasitic losses to my mpg but I'm experiencing greater losses than expected. I commute the same route daily - about 70-miles round trip through stop-and-go to 65 mph. I use Shell fuel only from one of two stations who discount steeply (ensuring supply turnover). I have the factory Continentals that are set cold at an accurate 40 psi at an ambient outside temperature of 28F. Accessory load is the same from day to day. My measured mpg calculated at fill-up has varied from just over 36 mpg to just over 42 mpg. Now the problem: The MFI average seems to be pretty accurate and I will check it at the same point into my daily commute (this is during the morning portion of my commute and 90% of this is with the cruise control set). When the local temperature spiked to 60F last week, the MFI indicated 48.0 mpg at my check point; however, at 8 or 10F I'm looking at less the 30 mpg at the same check point. I realize that the atmosphere is more difficult to punch through at colder temps but for the life of me, I'm at a loss to explain this much of a discrepancy. Others must be going through this too and I'm wondering if something is going on in the combustion process that I'm missing?
Edit: I neglected to mention that the route that I use for the MFI average figures are unaffected by traffic, from mile two to the end a dozen miles away is done with cruise control set at 62 or 64 mph.

VeeDub TDI - Are you referring to the electrical seat heaters, rear window defrost? Both? More than these?
 

VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
Jul 2, 2000
Location
La Conner, WA
TDI
2018 Tesla Model 3: 217,000 miles
I am referring to the 1500w auxiliary electric heating element that is part of the regular HVAC system (but not explained very clearly in the owner's manual) that supplements the output of the traditional heater core.

It's like a space heater in your dashboard that provides heat while the engine is still warming up.
 

psd1

Veteran Member
Joined
Aug 4, 2011
Location
OR
TDI
2006 Jetta 2013 Passat SE 6Man
VeeDub TDI - Are you referring to the electrical seat heaters, rear window defrost? Both? More than these?
All of the above, PLUS the electric cabin heater that is used to rapidly heat the cabin in the winter. Anything that puts a load on the engine is going to decrease MPG.

What you are seeing is nothing new, do a little research on this forum. Cold temps, cold fluids, more idling and less BTu's per gallon will ALWAYS lower FE numbers in the winter.

To prove the point I added up the 6 warm months (uncut fuel/warm weather May-Oct) and the 6 cold months (winterized fuel, Nov-Apr) My average MPG in the Jetta on uncut fuel was 53.45 MPG. In winter, my economy averaged 47.95 MPG, a 5.5 MPG loss. THe fact that you live in NE would lead me to believe that your mileage will suffer accordingly.
 
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Right Lane

Active member
Joined
Oct 23, 2012
Location
New England
TDI
2013 Golf
I am referring to the 1500w auxiliary electric heating element that is part of the regular HVAC system (but not explained very clearly in the owner's manual) that supplements the output of the traditional heater core.

It's like a space heater in your dashboard that provides heat while the engine is still warming up.
I agree VeeDub TDI! I read the manual avidly but VW's is painful to wade through! Two thirds of it - various 'notices' - should have been left on the editing room floor and I never did see a separate electrical cabin heater mentioned. I'd love to fire up Blue Tooth but will need an English translation first!
 
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Spanish Key

Veteran Member
Joined
Nov 24, 2012
Location
CNY/ADKS
TDI
2013 Jetta 6M
I'd love to fire up Blue Tooth but will need an English translation first!
I had no idea the thing had an electric cabin heater. I'm still confused by the AC turning on and off on its own.

As to the Bluetooth, if I can set it up, Pal, you can set it up. It's nice, BTW. I prefer that to trying to navigate the Ipod plug-in thing in the glove box. I can make it work, but getting to the right song/artist/playlist is a royal pain in the patoot.
 

VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
Jul 2, 2000
Location
La Conner, WA
TDI
2018 Tesla Model 3: 217,000 miles
The A/C will turn on any time you use front defrost, recirculate, or the minimum temperature setting. It also runs any time you put the system in Auto if you have Climatronic and you have to turn it back off if you don't want it on.
 

maniago

Active member
Joined
Jul 12, 2012
Location
Bowie MD
TDI
'13 Passat TDI 1/2SE-1/2SEL DSG
I am referring to the 1500w auxiliary electric heating element that is part of the regular HVAC system
I'm pretty curious as to how you've ascertained that there is such a heater, because, 1) a 1500W electric heater would draw 125amps at 12volts. That's better amp service than as most houses built in the '80s. 2) And you'd be talking a 3-ish gau cable run. Our starter might pull 80A as the only load on the car. But 125 while running? Not sure the Alt is rated for that 3) My VW service guys swear there's nothing of the sort in the car, or any other car for that matter. They tell me, if there were, it'd be a great selling point for VW, especially in Canada, so why hide it from anyone, ie the dealers/techs? 4) if you're off by a zero, ok that's ~10amps. Its possible, I suppose. Still begs #3.

If you've taken your HVAC apart and seen a coiled wire or several in a row, that's the fan resister bank, not a heater element. It gives you your 6 fan speeds. I don't know if this car uses that basic tech because the fan voltages could be computer controlled with a shade pole motor, I don't know.
More info please:eek: I'm plenty happy to be wrong and subsequently point it out to the dealer on how to unplug it so I get the mpgs back.
 

VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
Jul 2, 2000
Location
La Conner, WA
TDI
2018 Tesla Model 3: 217,000 miles
I'm pretty curious as to how you've ascertained that there is such a heater, because, 1) a 1500W electric heater would draw 125amps at 12volts. That's better amp service than as most houses built in the '80s. 2) And you'd be talking a 3-ish gau cable run. Our starter might pull 80A as the only load on the car. But 125 while running? Not sure the Alt is rated for that 3) My VW service guys swear there's nothing of the sort in the car, or any other car for that matter. They tell me, if there were, it'd be a great selling point for VW, especially in Canada, so why hide it from anyone, ie the dealers/techs? 4) if you're off by a zero, ok that's ~10amps. Its possible, I suppose. Still begs #3.

If you've taken your HVAC apart and seen a coiled wire or several in a row, that's the fan resister bank, not a heater element. It gives you your 6 fan speeds. I don't know if this car uses that basic tech because the fan voltages could be computer controlled with a shade pole motor, I don't know.
More info please:eek: I'm plenty happy to be wrong and subsequently point it out to the dealer on how to unplug it so I get the mpgs back.
  1. The Passat's alternator is 180 amps. That's right - 180 amps. It supplies ~14.2 volts.
  2. Check your alternator load at idle with the HVAC running in auto, A/C off, at a normal temperature setting (let's go with 73F). Alternator load will be around 60% (or more depending on other accessories, glow plug status, etc). 1500/14.2=105.6 105.6/180=59% *this is assuming you have Climatronic - if not Climatronic, set the heat for a moderate setting
  3. Don't believe what the dealer techs tell you.
  4. A 150 watt heater would do absolutely nothing.

We'll post some part numbers and pics from ETKA when we get home so you can see for yourself.

If you want your MPGs back, turn off the HVAC system until the engine is at operating temperature.

[EDIT] after reading some of the links below, there appears to be a discrepancy about the actual wattage of the aux heater, but it is in excess of 1,000 watts and is powered by a 100 amp fuse. For the sake of accuracy, I will revise my statement and call it a 1,000 watt aux heater until I can verify otherwise.
 
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maniago

Active member
Joined
Jul 12, 2012
Location
Bowie MD
TDI
'13 Passat TDI 1/2SE-1/2SEL DSG
I stand corrected then. Thanks. I'll go look for it. But I must say, though it is sadly understandable that the sales guy (whos been selling VWs since the 70's) wouldnt know, but the techs? Inexcusable. Especially if it seems its been on various TDIs since 2010....like not knowing if the car comes with a spare tire.
 

Cogen Man

Veteran Member
Joined
Jun 4, 2011
Location
Kingston, Ontario, Canada
TDI
2011 Golf TDI DSG.
"My VW service guys swear there's nothing of the sort in the car, or any other car for that matter. They tell me, if there were, it'd be a great selling point for VW, especially in Canada, so why hide it from anyone, ie the dealers/techs"?

I guess that's why my 2011 Canadian Golf TDI has said 1500W auxiliary dash heater. Can you change your VW dealership to somewhere else ? If your VW service guys don't know this, what else don't they know about servicing your VW ?? I'd keep my eyes on these guys. :eek:
All Canadian VW Golfs, Jettas, Passats come with the cold weather package. I don't believe all USA ones do. The OP's might not.
 
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IXLR8

Veteran Member
Joined
Mar 9, 2003
Location
Cushing, ME
TDI
12 Passat Platinum Gray, 02 Golf Black, 01 Jetta Black
RE: electrical load.
I don't know how much this matters in the big picture, but the other day I put the car in neutral and coasted down a gentle hill in town shortly after I left work. I was doing about 30mph, it was 23dF outside. With the climatronic on auto, MFI was showing 71mpg, when I turned the climatronic off, it showed 105mpg, my speed hadn't changed. When I turned the climatronic back on... after a moment the mpg's dropped back to 71. I was surprised at the load that the heating system put on the engine. So I am not sure you can dismiss the electrical load as not having an impact on winter fuel economy. I know my '12 Passat has taken a much lager hit in winter MPG's than my '02 Golf does.
 

Cogen Man

Veteran Member
Joined
Jun 4, 2011
Location
Kingston, Ontario, Canada
TDI
2011 Golf TDI DSG.
Cogen Man, can you confirm that it is 1500W?
I'll try VeeDubTDI. That is what I've been told. I'm at work right know. But the beast is parked inside were it's nice and warm. I'll have a look and see if there's anything on the unit that would confirm 1500W. If I can get to it. In the dash might mean a little work.
 
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VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
Jul 2, 2000
Location
La Conner, WA
TDI
2018 Tesla Model 3: 217,000 miles
RE: electrical load.
I don't know how much this matters in the big picture, but the other day I put the car in neutral and coasted down a gentle hill in town shortly after I left work. I was doing about 30mph, it was 23dF outside. With the climatronic on auto, MFI was showing 71mpg, when I turned the climatronic off, it showed 105mpg, my speed hadn't changed. When I turned the climatronic back on... after a moment the mpg's dropped back to 71. I was surprised at the load that the heating system put on the engine. So I am not sure you can dismiss the electrical load as not having an impact on winter fuel economy. I know my '12 Passat has taken a much lager hit in winter MPG's than my '02 Golf does.
Bingo. It takes a few seconds after turning the Climatronic back on for the heater to fire up - and it engages in two stages (based on VCDS observations) so it doesn't load up all at once. I noticed this the other day while Jason and I were messing around with VCDS - you can also hear a relay click under the passenger's side dash when it engages the heater... it's very quiet.
 

IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
Right Lane, it probably matters how far into your drive your check point is, as your car may not be up to temp yet on cold days. I haven't driven my Golf much this winter but I do notice it seems to warm up slower than my modified A4. I have a short drive to work (5 miles) and purposely get on the highway on cold days to get the car under enough load to warm it up. I think it's tougher in the newer cars with taller gearing, too. Babying it at 65 MPH may not be helping, actually.
 

VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
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Location
La Conner, WA
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2018 Tesla Model 3: 217,000 miles
Part number for the electric heating element: 1K0963235G

Impex will sell it to you for just under $300
 

Knarrly Viking

Veteran Member
Joined
Feb 25, 2012
Location
Washington
TDI
2015 Passat SE 6MT, 2 of them!
I've been turning the climatronic off when I can to use less fuel, just didn't realize how many amps the aux heater was actually pulling. Wow! So which is worse, having the climatronic set at 68F on a 30F morning, or having the climatronic off and just using the seat heater on low? I've been trying to do the later, unless I need defrost on the windshield.
 

MikeMars

Veteran Member
Joined
Mar 6, 2008
Location
UK
TDI
Vento 1.9 TDi (retired), A4 1.9 TDi (rear end collision), VW Passat 1.9 TDi (retired), Audi A2 1.4 TDi
Does it heat the coolant, or does it heat the cabin air?

The webasto in my car heats up the coolant by burning diesel. The later model-years of the A2 had the electrical heater mentioned above (not sure of the wattage either, but it is at least a kw).

Based on the scangauge figures, the diesel consumption figures of the webasto, and a lot of guesswork, my best guess is that when the temperature is below freezing, the fuel usage of my heater breaks even at 10 miles (so under 10 miles, it is wasting fuel overall, and over 10 it is saving fuel because the engine is warmer quicker). However under zero, I turn it on anyway, regardless of distance, to make sure the windscreen is clear of frost & mist. Also I cannot be certain of the precise numbers.
 
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VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
Jul 2, 2000
Location
La Conner, WA
TDI
2018 Tesla Model 3: 217,000 miles
I've been turning the climatronic off when I can to use less fuel, just didn't realize how many amps the aux heater was actually pulling. Wow! So which is worse, having the climatronic set at 68F on a 30F morning, or having the climatronic off and just using the seat heater on low? I've been trying to do the later, unless I need defrost on the windshield.
It will use less fuel to leave Climatronic off, although I would much rather be comfortable than freeze my ass off in a brand new car. I, for one, love the electric cabin heater.
 

IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
So I think I did make it work this morning. Put the fan on 3 and thermostat all the way to the top. Had warm air within 2 miles.
 
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