Strange new symptom

Over the past two days I noticed that my overall MPG jumped form an average of 38 to 45MPG. Strange, I did nothing different and drove the same as always.

The tank was down so I filled with fuel last night. Different fueling station than the previous tank.

This morning, for the first time ever, the car didn't start immediately when I turned the key after the glow plug light went off. I recycled the key and the engine turned over fast for about 15 or 20 seconds before the engine fired. It ran fine at that point, no smoke, no problems.

On the way to work I averaged 47 MPG!

I might detect the occasional slight odor of diesel. Not strong and I'm not sure it's even really there.

I'm at work now so I can't run a VagCom check but will when I get home.

Does this series of symptoms ring a bell for anyone? By the way the car has ~76K miles total.

I've noticed that warmer weather (40 degrees +) seems to have an affect on fuel economy compared to winter temps. But 38 to 45 is huge!

I wonder what the cetane of the tank you got that 45 with was? Hmmmmmmm....

No bells ringing here, but run this tank and see what pencil and paper works out to for mileage. I am wondering if there is a hitch in the reporting.

it's probably just the temps, I have noticed the same phenomenon with MPG and I haven't filled since the temps changed

maybe you unknowingly filled up with some LSD which was not winterized/barely winterized

If I filled up with LSD I would probably think I was getting better mileage too. Oh, you mean the fuel.

The car started fine when I left work, so maybe that is not at all related.

On the trip home it showed a far more (slightly less than) normal 36.3MPG.

Maybe it was the extreme winds. I never thought of it a car before but airspeed always equals ground speed, at least hopefully. I had a ~40KT tailwind on the way in this morning and a like amount of headwind on the way home. I can almost convince myself it makes sense. It's better than my usual flying luck though - I always seem to have headwinds in both directions!

Thanks to all who offered inputs and especially for the great 'tab', Dude!

Sip'n Diesel said:

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whoa, trippy

daedalus said:

The car started fine when I left work, so maybe that is not at all related.

On the trip home it showed a far more (slightly less than) normal 36.3MPG.

Maybe it was the extreme winds. I never thought of it a car before but airspeed always equals ground speed, at least hopefully. I had a ~40KT tailwind on the way in this morning and a like amount of headwind on the way home. I can almost convince myself it makes sense. It's better than my usual flying luck though - I always seem to have headwinds in both directions!

Thanks to all who offered inputs and especially for the great 'tab', Dude!

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I've seen strong winds add or substract 2-4 mpgs...

abctdi said:

I've seen strong winds add or substract 2-4 mpgs...

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8 mpg difference in my diesel chevy with a strong tailwind in wyoming. You can actually see the difference on the RPMs.

Skidor said:

8 mpg difference in my diesel chevy with a strong tailwind in wyoming. You can actually see the difference on the RPMs.

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They say that while cruising at highway speeds, about 60% of the engines power is used up to overcome air drag alone, and this increases significantly as speeds increase. The B5 Passat(and I'm assuming also the B5.5) have a drag coefficient of 0.27, which was, (and still is!!!) one of the lowest in the industry. Regardless, cruising on the highway at 120km/h, and hitting a head wing of say 40km/h, will put a dent in the fuel economy figures that you will immediately see, although I doubt that you will see a RPM increase in the tach gauge on this type of low Cd car. I do believe you though when you write, that you do see a RPM increase on your Chevy's most probable .40 Cd drag coefficient figure during a head wind .

It is pretty windy in southern Alberta as well and I see a difference between head wind and tail wind all the time. I also see a difference in elevation. I have a commute that is 50 km one way and a 1600 ft change in elevation. The fuel consumption is noticably and consistently higher going up.

Skidor said:

8 mpg difference in my diesel chevy with a strong tailwind in wyoming. You can actually see the difference on the RPMs.

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I assume you have an auto tranny and the torque converter is responsible for this.