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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 December 4th, 2018, 17:56   #1
jesus_man
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Default Affect of weather/climate on MPG's

Just curious to know if anyone of you have logged, even mentally, when you achieve your best MPG's and what the environment has been.
Of course, winter fuel could be a factor, but recently I have noticed that on the same winter fuel from the same station, I get better MPG on warmer (highs in the 50's & 60's) than on cold days. I also admit that I may "puff" my car for about 10 min on cold days.
Also, what about climate? Dry vs humid; high altitude vs low; etc...
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Old December 4th, 2018, 18:38   #2
da.hs
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2010 Golf: about 25% economy hit summer to winter (winter here is typically -20C). 2004 Golf was more like 10% - I've never found a very good explanation. MPG starts to drop around +5C air temperature, getting worse down to about -15C and staying the same thereafter. It isn't due to winter fuel or tires (though they may have some effect), it's noticeable hour to hour as air temperature changes. Using a winter front helps a bit: the temperature at which MPG starts to drop moves down to about 0C


I don't ever give it idle time to warm up. It's normally garaged.



Dealer mentioned when I purchased it that VW had redesigned the cooling system to give higher priority to warming the cabin in cold weather so that may be part of it - my normal run used to be half hour highway.
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Old December 6th, 2018, 13:30   #3
JesseTDI
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Winter blended fuel, increased idling time, and colder (thus denser) air all have significant effects on fuel economy in the winter. I usually achieve the best fuel economy when it's around 65-75 degrees out with moderate to low humidity.
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Old December 6th, 2018, 15:54   #4
scooperhsd
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It's a waste of time and fuel to leave your TDI idling to warm up. Start it, then maybe 30 seconds so oil gets everywhere in the engine, then drive off.


MPG - Best MPG is usually in the spring / fall, when you have moderate temps and summer fuel. Worst MPG is summer running the air conditioning and winter with winterized fuel. Worse in town driving, best on highway driving.


All this can be mitigated to some extent if you're disciplined enough in your throttle use.
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Old December 9th, 2018, 06:56   #5
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Well, the idling thing to warm-up the engine has been debated to no end. Sure, explain that to my wife ..... the psychology of letting the engine idle for five minutes is worth far more than any fuel saved by starting up and driving off. And, the engine will not (I say will not) cool off during those first five minutes of idling ..... even three minutes.

OP, I kept extremely detailed stats on my 2000 Jetta in an elaborate Excel spreadsheet. I bought the car in March, 2002 at 45k miles. I gave it to my son about a month ago at 371k miles. It consistently gets over 50 MPG, tank after tank of fuel. I always filled it to the max at each fill-up. The thing I noticed about the MPGs was the effects of my right foot on the accelerator. That one thing stuck out like a sore thumb.

Yes, the MPGs dipped a bit during the winter months, in my opinion, due to the winterized fuel, cold, tire roll resistance, cold stiff wheel bearing grease, cold transmission oil resistance, and a bit of idling. The cold probably had more to do with it than anything else. The ECU fuels to maintain the demand, whether it be 903 RPMs at idle or 2275 RPMs at expressway speed. So, until the engine is at full operating temperature, it will use more fuel on a 20f day than on a 70f to achieve that goal.

The Turbo makes up the difference in elevation changes!

I suppose a car operated primarily in a desert setting vs one in a wet climate would get better MPGs ... the road resistance due to pushing water alone would probably have a negative affect .. or, does the increased humidity have a positive effect.. Who knows?
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Old December 9th, 2018, 08:27   #6
jesus_man
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My car runs better after a few minutes of warm-up and I do LOVE sitting in a warm seat when the heaters are on. That, to me, is worth the fuel spent idling.

But it seems I achieve my best MPG in the heat of the summer, when humidity is nearly a mist in the air and I have the AC blasting. It would be my assumption that cool crisp dry days would be the best for combustion, but it just doesn't hold true on my car.
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Old December 9th, 2018, 10:00   #7
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My 2015 GSW gets substantially better mileage when the temps are around 60-70 deg F and humidity seems to make no difference. Now that temps have dropped below 40 deg F the car is back below 40mpg on the car meter where it was typically over 50 on the meter at higher temps. Driving the same route all the time so its definitely temp related and not just throttle or traffic. Pretty big drop in mileage and very disappointing. The 2006 I drove for almost 200K miles had a small change in the winter months but nowhere near as much. I believe its related more to the computer and engine than to winter fuel and cold bearings. The wifes 2009 JSW is about like the 2006 Jetta....about a mile per gallon or so rather than 10mpg change in winter.

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Old December 11th, 2018, 17:44   #8
turbocharged798
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The cold has almost no effect on my ALH. Usually 53MPG summer, just filled up and clocked 50.5mpg.


The winter blend fuel seems to have far more effect.
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Old Yesterday, 12:28   #9
miltoncf
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Quote:
Originally Posted by turbocharged798 View Post
The cold has almost no effect on my ALH. Usually 53MPG summer, just filled up and clocked 50.5mpg.

The winter blend fuel seems to have far more effect.
It should as it's lighter. My ALH wagon does better in summer, when it gets 48 mpg highway w/out a fuel additive such as PS or Howe's. In winter that drops at least to 45. Adding Howe's Lubricant now reduces the drop, and makes the engine sound like it did when new on high-sulfur diesel.

Last edited by miltoncf; Yesterday at 13:00. Reason: added hwy
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