2005 Beetle TDI, auto trans, poor mpg

[gil7bert]

Just bought a 2005 Beetle TDI 100,500mi. First check of mileage was 30mpg. Using A/C most of time. Got into independent shop changed out fuel filter. Shop says no intake blockage when fuel filter was changed. Just drove 150mi, still 30mpg. We will have timing belt changed at end of month since never changed and will get tire pres up, but what else could be causing the low mpg?

[almir]

1. tire pressure
2. dragging brakes
3. dirty air filter
4. clogged exhaust
5. bad ect sensor
6. thermostat stuck open
7. wide tires (extra rolling resistance) and heavy wheels (normal size is 195/65/15)
8. wheel alignment (creating extra rolling resistance)
9. torque converter lockup clutch in automatic trans not engaging and disengaging on time
10. clutches going bad in automatic trans (losing more and more of friction material will need more rpm to move the car the same speed comparing to when the clutches were in good condition.)
11. heavy foot
12. driving speed

there are more, but over-sized wheels from my experience are the worst

[bigochief]

I have a 2006 Beetle TDI BEW PD engine with 6 speed DSG tranny and consistantly get 37-40 back and forth to work. Last year, on a four hour highway trip, I got 43 mpg. I just completed a 100,000 service (changed timing belt) at 74,000 so I'll keep an eye on fuel mileage. I don't expect much change as the engine ran well prior to the service.

All items listed can surely lower your mileage but 30 is really low. Do you have a fuel leak or is your exhaust blowing black smoke?

[gil7bert]

Thanks ALMIR, good list to start from, getting the tire pressure taken care of today. will look and see if brakes look like dragging.

[gil7bert]

Do not see any black smoke, but will look closer
I will check on pavement for fuel leak, but don't recal seeing any. Thanks for the comparison.

[gt4494]

If it is leaking diesel you would definitely smell it.

[almir]

also you can try this: go to Autozone and get one of those red 5 gallon thanks. Wait until your low fuel light turns on then go to your gas station. Tell them you want diesel for $22 start pouring diesel into your 5 gallon thank. Monitor gallons meter on the computer to see if 5 gallons on the display screen match with your red 5 gallon tank. Put the rest in your vw. Drive until your low fuel light turns on again, then stop somewhere and put all 5 gallons from your red tank into your vw. Now you know that you really put in 5 gallons. Reset your trip odometer and drive until your low fuel light turns on again. See how many miles you get for 5 gallons.

For faster results you can find 2 gallon tanks or save 2 empty milk gallons. This will be the most accurate measure.

[bigochief]

Good point as the fuel gauge can vary. I normally get 200 at the 3/4 mark and 300 at the 1/2 on driving back and forth to work. The gauge seems to vary every time I start the engine. In addition, foaming fuel does make a difference. I can normally fit at least an additional 1.5 gallons once the fuel pump stops although perhaps not wise to top off to the top of the filler tube. A drawback of filling a tank with diesel is pumping slower to reduce foam.

[almir]

Originally Posted by bigochief

Good point as the fuel gauge can vary. I normally get 200 at the 3/4 mark and 300 at the 1/2 on driving back and forth to work. The gauge seems to vary every time I start the engine. In addition, foaming fuel does make a difference. I can normally fit at least an additional 1.5 gallons once the fuel pump stops although perhaps not wise to top off to the top of the filler tube. A drawback of filling a tank with diesel is pumping slower to reduce foam.

not only that fuel gauge is reporting wrong level, sometimes gas stations cheat (you think you are getting one full gallon, but actually you are getting less. I know that they have inspections by weight and measures people, but check it out when was the last inspection conducted. You will see little sticker on each gas pump.

[almir]

Originally Posted by gil7bert

Just bought a 2005 Beetle TDI 100,500mi. First check of mileage was 30mpg. Using A/C most of time. Got into independent shop changed out fuel filter. Shop says no intake blockage when fuel filter was changed. Just drove 150mi, still 30mpg. We will have timing belt changed at end of month since never changed and will get tire pres up, but what else could be causing the low mpg?

record your rpm at 50mph 70mph and 85mph, then compare your rpms with other members who have automatic trans. If your rpms are very close then you can eliminate trans problems.