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Discussion Starter · #1 ·
Since I bought the car 2 months ago I have been doing the same trip to and from work every day. In the beginning I was seeing about 47-48mpg. Somedays when it was a bit more clear I would see 50mpg. However, over the last 2 weeks this figure has dropped to below 43mpg. This morning I was down to 42mpg! (note; all figures are trip averages!). Is there any reason this may be happening? I have been trying to think of external factors that may be affecting it, but can only think of the change in weather as I haven't changed anything with the car. A few days ago I did replace 2 front tyres and went from the Dunlop Sports to Goodyear Excellence. However, this problems is older than just a few days so I can't see that being a deciding factor. If anyone has any ideas I would be most grateful. Please note all mpg figures are for a UK Gallon, not a US Gallon! My car is a 2002 130TDI Sport. THANKS!
 

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Tire pressure variations with temperature. Check tire pressures all around.

You could add a K&N Air Filter, 1+ mpg increase observed on highway for me [U.S.]



Disclaimer: Your results may vary of course
 

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Discussion Starter · #3 ·
I already have a Green Cotton Air Filter. I haven't changed my tire pressure and apart from the miniscule amount that might have escaped I can't find anything that would cause a 10-20% drop in MPG.
 

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Why would a different air filter make a difference to mpg on a turbocharged car with MAF metered fuel?
changes the airflow.
i had a k&n and put stock paper in and noticed a difference in mpg & response...bolth for the better.

as for the mpg drop
alot of factors will affect that, tire pressure, air temp and density etc.
try a fuel additive (cleaner)
vw also sells little bottles of fuel additive for tdi's that helps clean and lube the top end.
and boy, you have some nerve complaining about 43 mpg, i get 27hwy 15 streets:)
 

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Is it possible you hit a nail and there is a slow leak from one of the tires?
That happened to me once and the drop in MPG was one of the things that alerted me.
 

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Discussion Starter · #8 ·
Well, tonight I have checked the tyre pressures and sure enough, the rear two were very low. Down to about 20psi! So i've put them up to 32psi and will monitor the effects on the trip in the next few days.

Also, I recorded the temps on channels 4,5,6. Both 4 and 5 were at 107C after the car was on for maybe 3 mins, and channel 6 was at 120C. This strikes me as a problem, since air temperature was around 10C. Any ideas? This can't be good. I have noticed that the car is using coolant, not rapidly, but it does decrease to about half full over time (no further). I thought this might be due to it naturally finding it's level, but now I am wondering... any ideas?
 

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Have you had your fuel filter replaced? my gas mpg sucked ass for while. then I had my timing belt done and fuel filter replaced at the same time....hitting near on 300miles per tank now! I was lucky to hit 200 before.
 

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what should the tire pressure be for the front and back
you should be able to find that on your gas cap, what vw recommends anyways if your runnning factory size for rims and tires.. If you have bigger rims i think 2 psi per inch is a good guesstamite... think i have 33 in front and 30 in back right now, you can just to some playin around and find a psi you like comfort wise, tire wear wise, and mpg wise...
 

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pascal, I think you're worrying too much. Take a deep breath. :)

Adding air to your tires will help. Also, check the engine bay for any loose or deteriorating vacuum/boost hoses. This will affect the engine's response and could decrease your fuel economy. It may not even be noticeable yet.

Also, the temperature can have an affect.

-Mark
 

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Have you had your fuel filter replaced? my gas mpg sucked ass for while. then I had my timing belt done and fuel filter replaced at the same time....hitting near on 300miles per tank now! I was lucky to hit 200 before.

my gas is sucking arse but it could be cuz i floor it too much.. i get about 250 per tank with flooring it a bit. Maybe thats not that bad..who the hell knows.
 

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Discussion Starter · #15 ·
My concern over mpg is over. With some more air in the tyres I'm back up to around 50mpg! However, my climatronic diagnostic is still all over the place. The other morning channels 4,5,6 were respectively, 77,97,77C and this morning they were 40, 40,50C both readings taken after the car was on for 2-3 minutes. I don't understand how this can be possible when the outside air temperate is under 10C. Would it be possible that this is related to the fact that my coolant tends to be decreasing over time? Some sensor fault? Help please...


just to add, my car is a TDI and I get about 600 miles a tank (generally driving quite steady but also including a fair bit of single lane overtaking)
 
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