My pair of 2010 JSW at 10,000 miles.

These cars don't get the same mileage. I have been tracking the pair of them and have had the two employees swap them week in and week out for over 4000 miles and the cars don't get the same mileage. They are almost sequential twins as for production dates and VIN.

3 mpg difference.

Thoughts?

3mpg is a lot. Have you ever checked for rear wheel drag?

Other than that the DSG (if so equipped) may be programmed slightly differently.

That's all I got.

P.

Paul, both are 6 spd manuals. I have had both on lifts and didn't notice any noticeable difference in rear wheel drag through a possible sticky park brake.

They have the same Continental tires on them. Same wheels.

I'm gonna see if they size up to one another now with the oil and filters being just changed.

Next step is doing some VCDS logs.

Pretty strange.

Could be a tire I guess. Maybe I'll swap them all, car to car.

Rod Bearing said:

They have the same Continental tires on them. Same wheels.

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Tires all at the same pressure?

Maybe one needs a ECU update? Bad O2 sensor?

Same fuel in both? I don't think the fuel can make that big of a difference, but it could be a contributing factor.

I think second would be driving style. Do your employees drive both cars to the same locations in the same manner all the time?

And lastly, I know you said you didn't notice any detectable wheel drag between the two, but it could still be a factor. When sitting in my car and lightly pulling on the brake, I can feel the tension in the handle before the "Brake" light comes on. Is it the same way in either of your cars?

Are the cars the same colour? Maybe one is driven slightly more agressive than the other because it looks more agressive. 3mpg doesn't seem like much to me when you're talking about 40+mpg already.

I would check the alignment, check the camber, castor and toe of the front and rear of each and post up what you find.

My guess is that you have too much toe on the car with the poor fuel economy.

Is it possible to get something as complex as an ECU to function without any variability between units? When you factor in all the other systems its linked to throughout the car, it's not surprising, to me, at least, that one car could vary from the next, all other things being equal.

If you have that much variability in electronics, then manufacturing tolerances are horrible. With everything digital nowadays, and processors running at many megahertz, there is no reason for anything more than a few milliseconds' difference.

Piezo injectors are a different story. I believe they are still relatively new technology. On the other hand, they are supposed to be fast enough to pulse up to five times per duty cycle, so I wouldn't think they would have much variation between one unit and the next. Generally, any type of precision equipment is manufactured using very close tolerances.

I would go with the alignment idea posted above. Beside affecting fuel economy, tire wear is also greatly affected due to toe settings.

Maybe, and Maybe Not

gumaku1 said:

I would check the alignment, check the camber, castor and toe
of the front and rear of each and post up what you find.
My guess is that you have too much toe on the car with the poor fuel economy.

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It would seem to me that IF the toe was so far off to cause such a difference in F E,
there would be signs of the vehicle not being properly alighed, i e cupping.

I don't know if caster and camber would have that much affect, would they?

I wonder, are the brands of tires on both your JSWs the same?
The JSWs came with at least four different brands.

Three miles per gallon difference is 7.5 percent which does seem like a lot.



D

Figuring mileage with tank fill ups and pen and paper, or reading off MFD?

The cars have the same size rims and brand of tires.

I figure cost per mile and when I see discrepancies developing, I look further. In the case of these two cars, once the differences started to show up, I tested over a 4000 mile span very aggressively by swapping the two employees back and forth between the cars multiple times to see where and under what conditions there might be something different. Tire pressures were meticulously maintained as were both cars systems to match them as close as I could.

It's not weather, they are both driven in the same city all the time.

Swapping cars ruled out driving habits or route differences.

Same fuel was and still is used in both cars.

All my fuel calculations are done by my fleet manager with software on a computer..

In my experience toe difference would be even excessive tire wear, not cupping. Cupping is ususally from camber + toe, but it truely depends on the suspension geometry. The Jetta has a very good "conventional" suspension, so I suspect you would just have excessive even tire wear.

I would still like to see the alignment numbers comparing both vehicles side by side.

Also what you can do is measure the tread depth of each tire on each vehicle and compare.

At 4000 miles tire wear might be a very small difference, but it will be somthing to see, you will need to be extremely accurate in your measurement though (since you are only at 4000 miles)

The difference I am talking about will be at 20,000 miles one vehicle will have almost no tread and the other will be ~50% worn.

Derrel H Green said:

It would seem to me that IF the toe was so far off to cause such a difference in F E,
there would be signs of the vehicle not being properly alighed, i e cupping.

I don't know if caster and camber would have that much affect, would they?

I wonder, are the brands of tires on both your JSWs the same?
The JSWs came with at least four different brands.

Three miles per gallon difference is 7.5 percent which does seem like a lot.



D

Click to expand...

It has to be alighment

Rod Bearing said:

The cars have the same size rims and brand of tires.
I figure cost per mile and when I see discrepancies developing, I look further. In the case of these two cars, once the differences started to show up, I tested over a 4000 mile
span very aggressively by swapping the two employees back and forth between the cars
multiple times to see where and under what conditions there might be something different.
Tire pressures were meticulously maintained as were both cars systems to match them
as close as I could. It's not weather, they are both driven in the same city all the time.
Swapping cars ruled out driving habits or route differences.
Same fuel was and still is used in both cars.
All my fuel calculations are done by my fleet manager with software on a computer.

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If all else is the same as you say, tire brands, wheel sizes, etc, what else can it be?
Maybe you have a dragging brake from the parking brake cable being too tight, but I doubt that.
I think you said that you had checked that.

For your F E to be different by as much as 7.5 percent, there has to be a reason.

Do you have a good alighment person to go to in your area?

Too bad you are not here in Southern California as I know the perfect fellow to send you to!
He did mine, and found that both ends needed more toe-in, so it
now handles as I figured it should right fron the factory.

BTW, an alighment is no better than the tech doing the work.
It matters not what equipment he is using if he does not know what he is doing.
My man does and his forty years experience really shows in his work.



D

17 inch wheels?

Rod Bearing said:

They have the same Continental tires on them. Same wheels.

Next step is doing some VCDS logs.

Could be a tire I guess. Maybe I'll swap them all, car to car.

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I do not believe that Continentals came on the 16 inch wheels.

It will be interesting when you do some VCDS logs.

Also, if it is not alighment, perhaps your idea of swapping wheels
and tires combinations JSW to JSW will cause the F E to shift?

Please keep us posted as to what you discover. This is interesting, at least to me.



D

Pretty cool business vehicle. What business?

Maybe trade in the pig! These cars seem to have prettysolid resale.

Service issues yet? if you keep, will be interesting to track that.

I would write it off as driving style or route.

Have the employees swap cars and see what happens.

Why?

tedkidd said:

Cdi traded for 11 jswtdi

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Were there too many expenses with keeping up the MBZ, or did you simply want a wagan?



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Read ALL His Posts

rootbeerinacan said:

Have the employees swap cars and see what happens.

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Read everything he has said for content this time!



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Derrel H Green said:

Were there too many expenses with keeping up the MBZ, or did you simply want a wagan?

D

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Yep, and image inappropriate for my business. Beautiful car capable of crazy good mileage, but it was an indulgence that cost me in too many subtle ways. And you know what, the jsw keeps growing on me. Nice having a car the bike fits in without removing the wheels.

What mileage are you getting on the two cars?

Is the difference 5%, 10%?

They Do Indeed

tedkidd said:

. . . you know what, the jsw keeps growing on me.
Nice having a car the bike fits in without removing the wheels.

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Wait until next summer when you can get regular summer fuel and it will have more miles on it.
Watch how your F E will improve. That'll make the ol' Benz seems like a 'diesel' hog!



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Easy

timwagon said:

What mileage are you getting on the two cars?

Is the difference 5%, 10%?

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Easy.

Look at his Fuellies for each vehicle!

Looks like more than 15 percent, and remember, the TDI is a long way from reaching its' full F E.



D