I started tracking my MPG and the first thing I noticed was that most of the other Jettas on this site get between 30 and 40 mpg, while I get 20.
Any advice or insight? I have an 02 Jetta sedan with 115K on it. Just had the oil changed. I don't do partial fillups. I don't get cheap gas (like Wawa or Sheetz or Sam's Club/Kroger), I fill up at the BP where I work so the gas has the additive to clean the engine.
Most of the high-mileage Jettas are diesel powered on this site. My wife has one, and it's a nice small turbo diesel engine that really saves on gas and is hopped up enough at the factory to feel like a normal engine. They average 15+mpg more than the normal-in-the-US gas engines.
I agree with the 02 sensor. I scanned my coworkers saturn and his check engine light was coming on every once in a while and according to my scan guage II his code was still pending but he replaced the front 02 sensor and that took care of it.
You can always check your fluids, tire pressure, any unecessary weight in the car, handbrake staying on by accident when car drives, staying under 3000rpm will give you the best MPG.
A couple other things to check are the Mass Airflow Sensor. If you get your car scanned and you see a pending P1128 or P1127, that could be indicative of a bad MAF.
The MAF is what monitors air/fuel mixture and the codes above are for a lean and rich condition. Both of these conditions could reduce your gas milage. I had a bad MAF, and it lowered my milage by about 2-3 MPG.
Something else you should check is the fuel filter. If it hasn't been changed recently (last couple of years) it may be clogging, which will reduce mileage as well.
Everything else mentioned above should also be checked.
Actually if a fuel filter is clogged up, it will slow fuel delivery, actually causing an increased MPG. So will low fuel pressure in the case of a bad fuel pump. If you are burning less fuel (cause it isn't reaching the engine as well) you will get better MPG, but less performance. But this means you are running leaner, which could cause other long term problems if this condition continues for a period of time.
So leaner = less fuel = more mpg = engine runs hotter and can cause long term damage
Richer = more fuel = less mpg = engine runs rough, stinky, idle issues, hard starting, etc.
Its always best to make sure your car is properly tuned up and operating at its peak efficiency.
one more thing to take into consideration is what most of your driving consists of: in-town versus highway.
Depending on the engine, your Jetta's consumption rating is anywhere between 17 - 21 mpg for city driving. If you have any of the 2.8 L engines (VR6), then you're actually doing better than the rating with 20 mpg. Even if you have the 1.8 L engine you're still pretty much on-par with the city rating (21). For an almost 10 yrs old car your Jetta actually is doing pretty decent.
Contrary, if your driving is mostly highway, then you need to have it checked out (scanned, etc).
As far as "most of the Jettas" on Fuelly with 40+ mpg, as people have said it before, those are diesel powered engined. However, don't compare yours with those, as if you read between the lines you'll notice that some people "get" 49 mpg with 85 % city driving...yeah, right...
Only compare your mpg against your own car's rating.
Just an FYI Kroger Gas stations have a contract for the next 4 years with BP gas. That's what is in their tanks.
Also Im not a Jetta owner but I know alot about cars. if you have the same engine profile as someone else getting 10 more MPG then you. Check the basics first Air Filter (ever 10,000 miles) Fuel Filter (Every 30,000 miles) Spark Plugs (every 100,000 if you buy platinum plugs). Then move on to O2 sensors if you have over 100,000 and the O2 sensors are original then they should be changed.
I'd have thought that the journey profile was just as important as the engine. If somebody is doing 5 miles / day in stop-go city traffic they're going to have terrible MPG compared ot someone doing 80 miles/day at 60mph. But the trouble is that you generally don't know this from the site, so it is hard to compare like with like.