HELP!!! Gas mileage drop????
 

I have a VW passat '98. Love it.

Last week the gas light came on around 277 miles, this shocked the hell out of me considering I always get to atleast 390 miles before the light goes off.

This tank full same thing. Light came on around 280 miles, what is wrong???

I did get an oil change recently, could this have anything to do with it?

I am freaking out because I love my car, I just did a $1500 check up on it a little over 4 months ago.

Can anyone tell me what might be wrong with it?

Is it time to sell this beautiful '98 VW Passat with over 70K miles? :confused: :confused: :confused:

get a new air filter and some new belts maybe

check tire pressure, too. Also what engine do you have?

Is it running rough? I once lost a whole bunch of MPG, took in in to the dealer, and found out that the wire running the oxygen sensor back to the controller had come off, and since the controller couldn't figure out what fuel mix to use, it was running as fuel rich as possible.

Quick spot of solder, no charge, got all my MPG back. Best dealer experience ever.

I have the 4-cylinder turbo.

Any changes in your driving habbits?

What did you have done that costs $1500??

Has your fuel/water seperator been changed?

Do you check your tire pressure weekly?

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My advice, fill it up again and see how many miles you get, then worry.

-SF

Have you been using your air conditioner much more than usual?

That is the biggest waste of gas ever...that why I ripped mine off 2 years ago...my windows roll down:D

fuel filter, fuel pump....either or both could be going bad. i'd also check the air filter.

No check engine light? That would indicate an emission problem which would have a great deal to do with your mileage, as the person stated above about the sensor. As someone else said, what was the 1500.00 repair for?

<b>Pain Train</b>, here in Arizona, a car without A/C is a waste of gas. jk

Surprisingly, some (most?) cars get better gas mileage at highway speed with the windows rolled up and the AC on than otherwise. Windows down create all sorts of bad aero shit.

I just got new tires 2 weeks ago.

I think the drop may be because I was driving all highway miles untill about 3 weeks ago, and the new tires with nice thick tread.

I didn't think that it could drop this significantly but if most cars are 25/35 then about 100 mile drop could be due to none highway miles.

I am using my air conditioner 24/7. Again didn't think that would make such a difference.

I called VW they want to charge me $100 just to do a diagnostic on the sensor for the oxygen. That to me is insane.

$1500 repair was for:
new windsheild
new axel
alignment
full tune up
new hubcap
so on.....

Thanks for your help guys, again I think it is due to highway vs. none highway miles and the consistant use of A/C.

The lack of highway driving will do it.

In my previous car ('02 Focus), I got about 240 to the tank normal mixed driving, and 450 (nearly double!) on constant highway driving.

My suggestion: kepp your windows UP and use your cruise control as much as possible.

A failed O2 sensor is my best guess for a dramatic change in mileage. When it, or they, fail, you get a dramatic change in the fuel used. The first thing I'd do is have it changed. In fact, this is not hard to do, and O2 sensors are usually about $50 bucks, if that. They just screw into the exaust; use a wrench. Depending on how hard it's to get to, that's it.

A past g/f had a buick, when the mileage dropped from about 24mpg/avg over a tank to 15 the first thing I changed was the o2 sensor. Problem solved.

Yes, he's right about that, and the explanation in why a failed sensor will shoot your mpg is correct too.

New tires would not hurt your mileage unless they were severely underinflated.

The AC can be responsible for 5 to 10% change in MPG, they are no where near as demanding as many people have convinced themsleves with little dubious connections made into causes in ther own minds. A smaller engine will get hit harder from AC as it will use a higher percentage of the engine's available power. But still, we're not talking the kind of change to take you from 400 miles / tank to 300.

The other guy is right about windows and AC, drag vs power draw.
I've read time and time again that around 55mph you might as well run the AC, because the having the windows open causes so much drag that you're burning just as much, if not more fuel to make up for it, you may as well run the AC. Think about it. With the windows down, your car is a big scoop running down the highway. At enough speed, scooping in all that air is going to eat more fuel than AC. Again, smaller cars take a bigger hit. If your AC compresser was seriously fucked up, then I could see incredible amounts of extra drag on the engine. But, I think at that point the compressor would be so jacked, you'd not have a functioning AC.

If you have made a huge change in the mix of driving you do, it MAY be responsible. When I do almost all freeway in my car, I get 32mpg/over a tank. When I end up doing city running around, I'll get 23-25. Over a tank, that'll add up to a big difference in total miles driven over a tank.

I'd have the o2 sensor checked/replaced. Beyond, that you need to be looking more at what kind of MPG your getting over a tank, considering in your type of driving, instead of miles per tank. While it's an easy figure to see on your trip odometer, it's not a good value to use when deciding if your car is running right.

FIll your tank. Reset the trip odometer.
Next time you have to fill up, devide the number of miles driven on the trip odometer by the number of gallons you just put in to fill the tank (which = the number gallons you used to drive those miles.) That will give you miles per gallon. If you're getting near what your car is rated at in city/hwy driving, then you're just experiancing shock over a change in expected mileage as a result of changing your driving mix.
But, if you're getting 13 mpg, in city driving, and the car is rated at 29mpg city, you've got a mechanical problem.
Generally, the actual per tank mpg is somewhere in between the factory rated city/highway mpg figures, leaning towards what the majority of your mix is.

Little different in Canada I guess:D

Umm my friend a VW mechanic said the only problem with changing an O2 sensor on a passat is you have to pull the engine to change it.

Hole-y crap that would suck! Where'd they put the damn thing? Inside the turbo housing?
Seriously, that sucks nuts. O2 sensors, in my experiance, are just downstream of the header/manafold. On my Lancer it's just sitting there in plain view; her CR-V it's chillin too. WTF did they do with it? If any one out there knows what kind of fucked up mounting position would require an engine pull, I'd love to hear about it.

its probably your MAF sensor. go check out www.vwvortex.com if you havent all ready. the BEST place for your Vdub questions.

also changing the O2 does NOT involve pulling the motor on your 1.8T. if you had the W8 motor then yes it would indeed need to be pulled.

I can relate...

I have a 93 Chevy Lumina 4DR Sedan, I can get nearly 30mpg with all highway miles... ...put me in stop and go traffic and I'll get less than 20mpg, somtimes 15mpg.

So, changing from all highway to all city can lessen your mileage per tank as much as you've seen it. (Especially with a turbo-diesel)

-SF

Yeah, I'm gonna go with either a MAF, O2, or possible ignition control module on this thing. The cars are known to eat any one of those items. I don't think an O2 will be cheap for that thing, either. Some are, but most are $80 or more, some near $200.

i think you are referring to the coil pack and not the ignition control module thing. vw did have a recall on coil packs but i believe it was for MKIV (99' and up) vehicles.

Just go to Auto Zone/Pep Boy/Whatever and get your codes read. It's free and it'll tell you mot of your problems.

if its an O2 sensor it should give you a check engine light saying it is running rich/lean.