Do you trust the onboard MPG meter?

My dash MPG is always higher by about 10 MPG. I use Fuelly for about 2 years now, and their app always says that I'm 10 MPG less than what the car says. I always fill the tank to the top, I even wait for the foam to settle, and make sure the tank is completely full. Any way to adjust for this variance via VCDS?

relumalutan said:

My dash MPG is always higher by about 10 MPG. I use Fuelly for about 2 years now, and their app always says that I'm 10 MPG less than what the car says. I always fill the tank to the top, I even wait for the foam to settle, and make sure the tank is completely full. Any way to adjust for this variance via VCDS?

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The average fuel consumption is based on averaging the instantaneous fuel consumption versus miles since reset (trip meter)... The instantaneous fuel consumption drops when you accelerate, and goes up to as high as 200, then --- (zero fuel use) when the fuel is cut off (foot off pedal, decelerating in gear). I think that is based on volume pumped (metered fuel). The fuel tank level is not used for either one of these calculations.

The fuel tank level IS DEFINITELY used for calculating range, based on average mpg "so far" on the existing tank.

If you put the car in neutral, and let the car idle while you decelerate (with or without brake), the fuel flow is on to maintain idle, and you see consumption. That is why you see a number (mpg) while it idles in neutral....BUT, If you leave it in gear while you decelerate, and lift your foot off the throttle pedal, fuel is shut off (--- shows on the fuel consumption display), zero consumption until you press the clutch, or the throttle. When you press the clutch, the fuel must turn back on to maintain idle, and you see a number (mpg)... These cars are EFFICIENT!

I, too, have a 2013 Passat TDI and have also seen 57 mpg several times on long trips. This, coupled with finding diesel at $2.06 as we travel south, has made this an incredibly inexpensive car to drive on trips.

dubStrom said:

If you put the car in neutral, and let the car idle while you decelerate (with or without brake), the fuel flow is on to maintain idle, and you see consumption. That is why you see a number (mpg) while it idles in neutral....BUT, If you leave it in gear while you decelerate, and lift your foot off the throttle pedal, fuel is shut off (--- shows on the fuel consumption display), zero consumption until you press the clutch. When you press the clutch, the fuel must turn back on to maintain idle, and you see a number (mpg)... These cars are EFFICIENT!

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I was wondering about this for quite a while: my dash shows 0 instant consumption whether I coast in neutral or in drive (to be more detailed, instead of the 3 digits normal MPG format, for example 50.2 MPG, it shows ---MPG). Do you know if the injectors for a 2006 Jetta (code BRM) stop delivering fuel while costing in neutral, or that applies only for the newer engines?

Most cars with electronic injection, gas or diesel, do this. Including the 2006 Jetta.

relumalutan said:

I was wondering about this for quite a while: my dash shows 0 instant consumption whether I coast in neutral or in drive (to be more detailed, instead of the 3 digits normal MPG format, for example 50.2 MPG, it shows ---MPG). Do you know if the injectors for a 2006 Jetta (code BRM) stop delivering fuel while costing in neutral, or that applies only for the newer engines?

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Check again.
Coasting in neutral, you are using fuel to maintain idle. You will see a number (more than zero mpg). BUT... Coasting down in gear, fuel shuts off, --- shows in the mpg display (zero consumption).
You have DSG. It is smarter than a slushbox auto trans. Your car is in gear when you lift your foot off the pedal, so the fuel can be shut off... ---
ALSO try this, if you BARELY touch the brake while coasting, but do NOT actually press it hard enough to engage the pads on the rotors, it downshifts!!-engine breaking!! Try it. Cool huh? Saves your brake pads. Same thing happens if you press hard enough to engage the disc pads, but it is less obvious. This is a DSG capability. My 2010 JSW did this. It was the only DSG is owned-it drove me nuts, like all automatic transmissions! Just not for me, no matter how sophisticated. My '03 JSW (see below) three pedal conversion is under the wrench. Chomping at the bit!

The mpg display is definitely adjustable (sorry I don't have instructions or a link) via VCDS. I have recalibrated every VW with MFI I have owned. My current Passat was 2-5 mpg optimistic before recalibration. Now it is accurate within 1 mpg.

I reset my tripometer at every fill-up and hand calculate just about every tank. Fill until it clicks off then slowly fill to top of neck. I get almost 800 miles for every tank and ~ 50 miles for every hash mark on the fuel gauge. 140 miles/day commute, fill once a week.

dubStrom said:

Check again.
Coasting in neutral, you are using fuel to maintain idle. You will see a number (more than zero mpg). BUT... Coasting down in gear, fuel shuts off, --- shows in the mpg display (zero consumption).
You have DSG. It is smarter than a slushbox auto trans. Your car is in gear when you lift your foot off the pedal, so the fuel can be shut off... ---
ALSO try this, if you BARELY touch the brake while coasting, but do NOT actually press it hard enough to engage the pads on the rotors, it downshifts!!-engine breaking!! Try it. Cool huh? Saves your brake pads. Same thing happens if you press hard enough to engage the disc pads, but it is less obvious. This is a DSG capability. My 2010 JSW did this. It was the only DSG is owned-it drove me nuts, like all automatic transmissions! Just not for me, no matter how sophisticated. My '03 JSW (see below) three pedal conversion is under the wrench. Chomping at the bit!

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Thanks for the tips, I agree with everything you say. I double checked: whether I coast in neutral or gear, the display still shows the same consumption: --- , which I believe is 0