Too good to be true?

Did our first road trip with the Jetta, and I'm getting mpg numbers that look waaay too good.

Speedo is correct according to the "your speed" signs as we drive, which tells me the odo should be off, running 205/65 tires on stock rims. Stock tire size shows 195/65.

The distance from King City where we filled up to our house is shown to be 107 miles, the odo read 107.8 at the station I went to, which is about right. It took 1.955gal to fill it back to the top of the neck (ventectomied), which would mean we got 55mpgs while doing 70-75mph pretty much the whole way.

Is this really true????

....the speedo is set to read low, but the ODO is correct. The adjustment is made between the odo and speedo....i hope this makes sense, it did in my head

I run the same size tire in the winter, and my speedo is still out (only by 3 km/h vs 5 km/h with 195's), but the odo reads a little fast, based on MM on the highways....

Speedo's read high stock, so if you get a ticket you can't blame the speedo. Odo is correct with the stock tires. My tires go 17 fewer revolutions per mile, so there should be a % correction for the odo in order to calculate true mpg's. Even then, my mpg's driving 70-75mph seem pretty phenomenal. The B4V gets around 41 at 70mph, granted it's a bigger and heavier car. Just having a hard time wrapping my head around these mpg's, but in a good way.

FWIW - I get about 54 MPG on Cruise control set at 63 MPH (GPS speed not speedo which on my car reads higher).

Hope that helps.

Andrew

MY green Golf will show right around 57 mpg running on the flats at upwards of 70 mph. I need to get another UltraGauge so I can see what insane numbers I get out of my "new" blue Golf which has a 6spd in it.

Reality is that larger tires help with freeway/ highway MPG's and hurt a little in town.
I never trust two gallon mileage checks for the overall. A round trip with at least 4-5 gallons is my minimum.
I like to run full tank checks, however, it takes a good drive to get one of those

I agree about the larger checks. I'll be doing mixed now that we're back home, which looks to be about 41.

On the way down south, we hit horrible headwinds, driving rain, and sat in a backup that got us 10 miles in 2 hours. For that tank, we averaged 43mpg's over 282 miles, which was pretty doggone impressive by itself.

We'll do the same road trip in May, so we'll see what the roundtrip mpg's are then. I'm still pretty amazed. No wonder everyone says the ALH platform is the ultimate TDI!

Keep in mind, it is really hard to get the same exact fill with all the foaming and such, wouldn't trust a 1.9 gallon fill to be that accurate.

My ALH with .205 nozzles and a Stage 3 tune got 52 MPG at 75 MPH with 4 adults and their luggage. I have a Bluetooth OBD II interface using Torque Pro and The "Fuel Economy" app that works with it--which is free-- and it reads very accurately as far as I can tell so far. YMMV.

Today my UG showed 51 mpg's on a short, 10 mile trip which was mostly highway; the engine was still pretty warm when I started out. I can only imagine what a much longer trip would have netted.

Best practice is to track every fill-up, calculate every tank.
2 gallon fill is not an accurate measure, too small.
But they will get 50+ at 65-70, results vary.

61 fill-ups with my car and I'm averaging 50.3 mpg. This includes some early "poor" FE due to the car needing work. Wife's car with 67 fill-ups is averaging 49.3 mpg. Both cars are configured the same: Malone stage 2 and DLC520 nozzles.

i used to get 50 to 53 MPGs in my 1990 civic DX pretty regularly on the highway between windsor and toronto. it isn't 'unbelievable' at all. but a nice tail wind REALLY helps fuel economy. if I was heading into the wind, i could drop into the mid 40s pretty easily.

I think those numbers look fine. Things to keep in mind:

1) A smaller number of miles on a smaller number of gallons obviously makes any error (or atmospheric condition) exacerbate poor mileage or over-report good mileage. The claims that it doesn't really tell you anything aren't quite accurate, it's just that Fred's vets are used to evaluating claims over longer distance, since these better represent the overall ability of the driver & condition of the car.

2) The speedo reads low on stock wheel/tire combinations because of ECE/German law. The ODO is generally spot on for these combos. Swapping to taller diameters will impact both. Your natural speedo error may be (mostly) gone, but as you know, the taller diameter is under-reporting mileage by, what, 2%? The actual sizes of tires are often not what manufacturers claim, so the only way to know your real mileage error, is to do known-distance runs, with GPS (which is not always going to provide spot-on distance traveled, but serves as a good backup) and compare to your ODO. Without doing this, you may be adding 2% to your mileage in error.

3) Taller tires do not necessarily help with FE on the highway. See Ernie's posts from way back at the start of Fred's to read more. Bottom line, FE and tire interactions are so complex, it's often quite difficult to separate out the impacts of tire size, compound, width, height, weight, etc. on engine RPM, Cd, etc. That's not even speaking to changes in the wheel.

I have every mile and every drop of fuel / additive tracked on my car since new, and the same for (her) Jetta for 150k miles. I've run various comparisons and tests with wheel / tires combos, where we traveled the same route, at the same time, same speed, and the main variables were reduced to driver, wheel-tire combo, and Cd. Even these tests aren't going to provide perfect accuracy, but they're pretty good. Best result? 195/65 LRR on lightweight wheels, although I bet a more narrow tire would do better.

I've gotten pretty stinkin' good at filling up to the same spot every time. I wait for the foam to go down, rock the car to "burp" the tank, and don't stop until the fuel is just below the "spillway". I have to admit, having a 25 gallon capacity in the B4V has really spoiled me.

MarsBar said:

I have to admit, having a 25 gallon capacity in the B4V has really spoiled me.

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Would be nice if that tank fit in my Jetta.

I use a free app on my iPhone, Mileage Keeper. I have to enter the ODO mileage and Gal or Liters used per fill up. Since I started using it 7/22/2016 my average to date is 47.5.
My lowest tank was 42.8 in Jan not really running right to 53.4 last September.
I've been using my UltraGauge since last Summer & it's not ever close. It finally let me enter my refuel amounts but only on a partial tank fill. But I love it for timing, boost, and MAF readings! It's like having a VCDS on your dash.
I'm so happy to have you guys for info, same for me, you all are the reason I bought an ALH, and Dweisel is the reason I bought a 5 speed Beetle.
Dave

Dave, if you get your UltraGuage calibrated correctly you should be pretty darn close. My car has been running for over a year and a half (close to 2 years?) with an UltraGauge and, after recalibrating post new injectors and tune, I haven't touched it; I'm within about 2% of what hand calculations come out to. All said, I struggle to get the wife's UltraGauge to stay consistent: not sure if it's her driving or something else.

UhOh said:

Dave, if you get your UltraGuage calibrated correctly you should be pretty darn close. My car has been running for over a year and a half (close to 2 years?) with an UltraGauge and, after recalibrating post new injectors and tune, I haven't touched it; I'm within about 2% of what hand calculations come out to. All said, I struggle to get the wife's UltraGauge to stay consistent: not sure if it's her driving or something else.

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That's great!

I can only get my UG to add fuel in the partial fill up only, for about three months it wouldn't let me add at all. It did diagnose my timing problems. The timing is so critical in where the power comes in, to much advance power comes in late or not at all, to low, hard starting or no start. It also let me know my thermostat wasn't was only letting the engine reach 170. Now that Blue is running like she should, I'm having way to much fun on hills & entrance ramps, but I do know that my Beetle is capable of 50MPG in the warm weather and that's why I wanted a TDI ALH!

MK4ever,
Dave

Dave, are you saying you can't do a full fill-up? It's (facing the front of the unit) the upper right-hand toggle (in the rear), you just hold it up until it registers.

For sure, these devices can take a lot of fun out of driving these things! Constant reminder that I need to lighten up on the right foot!

UhOh said:

Dave, are you saying you can't do a full fill-up? It's (facing the front of the unit) the upper right-hand toggle (in the rear), you just hold it up until it registers.

For sure, these devices can take a lot of fun out of driving these things! Constant reminder that I need to lighten up on the right foot!

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Yes, It won't allow me, just changes screens when I push up or down button. I understand how to accomplish the task, but!

SaxmanKana said:

Yes, It won't allow me, just changes screens when I push up or down button. I understand how to accomplish the task, but!

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Isn't it the bottom button that is supposed to change screens?

If the gauge isn't working as it should I'd look to have them replace it.

I'll have to look into that, thanks!
Dave