03 mk4 bad milage, running out of options.

[windyhill]

03 mk4 Jetta, 5 speed, 15" wheels.
I'm frustrated with my current milage, just verified it on
Coming back from a 25mile trip after warming up the car. All highway Im getting a crappy 37mph.


Here's what I've done since I got her( in the last year)
New timing belt (done right)
New thermostat
New MAF
2 1/2 ID parts down pipe
Cleaned intake
New air filter
New injector nozels injectors set up by Frank
Changed oil and filter
Snow screen clean

Most recently
New NVT17 turbo
Rocketchip Stage 4 tune
3 bar map


My turbo was the last thing to go and was replaced and the car was retuned by Jeff. I used to get around 43mpg and about 650 miles to my better tanks. That was mixed driving.
I need some other ideas as to what might be wrong. 37 mpg on the scan gauge sucks.
It seams to run fine. Any ideas would be appreciated.

 

[Seatman]

Try measuring it the old fashioned way, I recently started using an additive that improves the mpg but the gauge in the car reads less, it's just a guess using the crank sensor. Like if your car is burning the fuel better it wont be so violent on pushing the pistons down which will change the crank sensor reading if you see what I mean.
Instead of one big bang the fuel will be burning smoother and more complete.

 

[jettawreck]

25 mile "trip" tells you nothing. A three tank average gives you some idea.
Big turbo, nozzles and tune isn't probably the optimum mileage setup regardless. What speed is your "highway" driving done at?

 

[windyhill]

I keep it at 65 or under, and try not to get on it to much. I also let it cost on the down hills. I realize a 25mile trip isn't a good indicator but around 550 miles on a 14.5 gal tank is. My brother just got 1000miles on a tank

 

[Bob_Fout]

I keep it at 65 or under, and try not to get on it to much. I also let it cost on the down hills. I realize a 25mile trip isn't a good indicator but around 550 miles on a 14.5 gal tank is. My brother just got 1000miles on a tank

1000 miles is unrealistic and takes a LOT of hypermiling. Don't ever try it...

550 miles to 12 gallons (when the fuel light comes on, assuming unvented) doesn't seem unusual, that's 46 MPG. Especially with mix driving.

That being said, what IS your actual MPG? Miles traveled / Gallons used.

 

[Bears Fan]

I keep it at 65 or under, and try not to get on it to much. I also let it cost on the down hills. I realize a 25mile trip isn't a good indicator but around 550 miles on a 14.5 gal tank is. My brother just got 1000miles on a tank

500-550 is my average per tank.

 

[Herm TDI]

Most of the "Old School" fuel economy rules still hold true.
Wheel Alignment
Tire pressure
Type of tires (cheap tires get expensive at the filling station)
Scheduled air filter maintenance
check for binding or draging brake pads (re parking brake cables)
Hold crusing speed below 70 MPH
Remove unused roof racks
Remove needless weight from trunk / cargo area

TDI specific
Double check your static timing and verifi TDC crank/cam/pump
Use only VW OE engine temp sensor

 

[windyhill]

Most of the "Old School" fuel economy rules still hold true.
Wheel Alignment
Tire pressure
Type of type (cheap tires get expensive at the filling station)
Scheduled air filter maintenance
check for binding or draging brake pads (re parking brake cables)
Hold crusing speed below 70 MPH
Remove unused roof racks
Remove needless weight from trunk / cargo area

TDI specific
Double check your static timing and verifi TDC crank/cam/pump
Use only VW OE engine temp sensor

looks like im averaging around 40 mpg after the last tank mixed driving. Still would like to improve it. I have new brakes and rotors on the rear, and New VW thermostat, engine temp sensor seams fine.

Tires may have something to do with it. there getting pretty warn down.

 

[Whitecloud1]

Time to chill a little..... Every one of these has great info to follow to get your MPGs up.

With all the "goodies", you may be sacrificing some MPG for the torque and HP.

What are your tires? My original Mich's were the best MPG but absolutely horrid for winter driving. BFGs were best over all.....3 sets worth.

Use the info by the others from above(every one of of their recommendations would be mine), run through a couple tanks and let us know what you're getting.

My '02 is still hitting 46mpg with the chip and original injectors.

 

[jettawreck]

Worn tread on your tires are the best for mileage. New tires with full tread rubber will cause a definite milage loss, as will wider tires.
40 mpg with "mixed" driving and your mods (depending on how you drive them) isn't horrible, actually respectable.
Do a couple tanks with accurate fills (vented/filled to the rim) and see what it really is. The first tank after a "fill to the rim" may be a bit dissappointing, but the next ones will be accurate.

 

[windyhill]

Thanks guys, I'll run a few tanks.

My brother is killing me, he just got 1047 miles on his last fill up (Stock 00 Jetta 5 speed 170K). That's the second tank over 1000 in a row. I keep telling him something must be wrong with his odometer or his speedometer but he checked it out on the highway and says it's good. and that's not overly long trips either.

 

[yatzee]

Thanks guys, I'll run a few tanks.

My brother is killing me, he just got 1047 miles on his last fill up (Stock 00 Jetta 5 speed 170K). That's the second tank over 1000 in a row. I keep telling him something must be wrong with his odometer or his speedometer but he checked it out on the highway and says it's good. and that's not overly long trips either.

he knows better fuel economy tricks that you... lol

All joking aside - 2 people driving the same car will not be able to get the same economy. Different driving styles etc.

 

[jprich7]

Thanks guys, I'll run a few tanks.

My brother is killing me, he just got 1047 miles on his last fill up (Stock 00 Jetta 5 speed 170K). That's the second tank over 1000 in a row. I keep telling him something must be wrong with his odometer or his speedometer but he checked it out on the highway and says it's good. and that's not overly long trips either.

1047 miles / 14 gallon tank = 74.8 mpg. (I believe the tanks are 14.5 gallons but surely he doesn't run it completely dry)

I'm not suggesting your brother is lying but he may be calculating his mileage improperly.
If not congrats because that would be some awesome efficiency!

 

[Bob_Fout]

To get 1000 miles from 16 gallons (including vent) takes some excruciatingly slow driving.

 

[jettawreck]

1047 miles / 14 gallon tank = 74.8 mpg. (I believe the tanks are 14.5 gallons but surely he doesn't run it completely dry)
I'm not suggesting your brother is lying but he may be calculating his mileage improperly.
If not congrats because that would be some awesome efficiency!

The official tank capacity is easily exceeded by venting as you fill it. Do a search for "ventectomy". Venting and allowing the diesel fuel foam to dissapate will allow you to fill the expansion tank (left over gasser parts used) and the filler neck to the rim. It won't get you any better fuel mileage, but it is the best way to get accurate fill levels. Aprox 17 gal on an empty tank is possible. The occasional 900 mile tanks I've run usually fill 16.1-16.4 gal. Right around 55 mpg average for the tank when things go well. Never run one out yet.
I have my reservations about 1000 mile tanks unless someone was pretty dedicated hypermiler type.