Why is my mileage so much lower than others claim?

[ORCoaster]

I can pull 50, but it ain't easy, my motor is tired not tight, and it is flat here. My f250 mod set me back 2 mpg, and my odometer reads up to 3% high, which I proclaimed a while back.
Same as before, I essentially try not to hit the gas or the brake lol. And I can squeeze high 40's like this.

Well now that you have loaded the front end with lead it is going to be easy to exceed your average Fuelly.  I had my car loaded down to within two hundred pounds of max gross last week on my run north.  But it looks like I got great mileage.  Over 300 miles on just over a half tank, maybe 2/3rds which is near the upper 40's.  I will know the truth on Thursday when I do the refill at the same station thing.  If the number is over 48 I am going to mark it up to one of three things, a. a new LeBra on the front, b. new wing window open on the drive up, c. a tightening of the OUT bolt to stop a weeping leak I didn't know was happening.  By doing that I also picked up a pound or two at cruise on my IP pump. 

You decide which is the correct answer to getting better mileage.

Even 45 MPG would be great considering I was nearly maxed out and doing 65-70 most of the way.  It just ran nice and smooth. 

[cervelorod]

I can pull 50, but it ain't easy, my motor is tired not tight, and it is flat here. My f250 mod set me back 2 mpg, and my odometer reads up to 3% high, which I proclaimed a while back.
Same as before, I essentially try not to hit the gas or the brake lol. And I can squeeze high 40's like this.

What's a F250 mod?

I check per tank, but it has been 33-34 mpg since I purchased it 2 years ago.  I drive it hard, use the throttle more like a switch than a variable resistor...

I have checked mine odometer via GPS with the same error your are seeing ~3% with my summer tires.  It is worse with my winter tires.

Thanks,
Rod

[rabbitman]

Someone else on here was having the same rotten mileage problem, can't remember if he solved it though.

[wdkingery]

I can pull 50, but it ain't easy, my motor is tired not tight, and it is flat here. My f250 mod set me back 2 mpg, and my odometer reads up to 3% high, which I proclaimed a while back.
Same as before, I essentially try not to hit the gas or the brake lol. And I can squeeze high 40's like this.

What's a F250 mod?

I check per tank, but it has been 33-34 mpg since I purchased it 2 years ago.  I drive it hard, use the throttle more like a switch than a variable resistor...

I have checked mine odometer via GPS with the same error your are seeing ~3% with my summer tires.  It is worse with my winter tires.

Thanks,
Rod

My f250 mod was running the car with 2 truck batteries installed
My mpg is quickly sliding! 43.5 today! But I ran the piss out of it for about 80 miles so. I think I could have hit 45 hhad I not. 47 with 1 battery. But it's goin down!

[ORCoaster]

The F250 mod is not going to be in high demand here I can forsee that.  Get ready for the cold weather and crappy mileage.  I may have to drop the wax treatment sooner than later as the weatherman says colder and wetter for the PNW this year.  I can't afford to be stranded in Portland with a plugged filter.  So I am packing a spare. 

[cervelorod]

We've been below freezing at night for over a week now.  Diesel prices jumped .10 - .20 two weeks ago, figured it was winter blend.  Hooray higher prices and less btu's.... Cleaned my side of the garage so I could park inside too.

Rod

[wdkingery]

yes i'm wondering if the weather/quality of fuel is having something to do with my mileage.
also, i stopped waxing (or any additives) about 3 tanks ago, so maybe that has played into it.

i had a dream  i got rings for Christmas lol

in the spring i'm hopin to ring some pistons, and get my VNT on (with theman53's mount he fabbed me) and then we'll see what we can shake loose.

by the way, my car is freaking loud.  OR Coaster (or anyone really) at 65+ is the engine just damn loud on yer car? i mean .. it's to the point wifey is now bringin the ear muffs she wears at the range for any highway travel she does with me. and i noticed i can still listen to rush limbaugh with the muffs on, so now i too am wearing them at all times.

what gives with that? why's the motor just make .. that much f'in noise??

[8v-of-fury]

You have an exhaust leak. The motor itself does not make a lot of noise.. but the 23.5:1 combustion does

Check it out, bet you'll find a hole somewhere in the tunnel.

[rabbitman]

by the way, my car is freaking loud.  OR Coaster (or anyone really) at 65+ is the engine just damn loud on yer car? i mean .. it's to the point wifey is now bringin the ear muffs she wears at the range for any highway travel she does with me. and i noticed i can still listen to rush limbaugh with the muffs on, so now i too am wearing them at all times.

what gives with that? why's the motor just make .. that much f'in noise??

Same here, I notice if I stop and my music is still playing I think "man that's loud", but it has to be to hear it over the engine, exhaust and studded tires...........and lots of rattles .

[ORCoaster]

Not engine loud, nor road noise loud.  Thanks to a healthy application of rubber in the doors, floors, and though out the back.  Not a complaint there.  I had a bit of an exhaust noise until I tore the pipes apart and reset them.  I think the PO ran over something in the woods while fishing and just didn't care. 

I do notice more road noise with the sunroof or the "wing", man I love them things, windows open but that is to be expected. 

[Toby]

Mileage claims based on one tank can vary substantially.  (How do you know how full it was when you started the run and how do you know you filled to the exact same point?)   

The proper way to do it is simple, if slow. You need to take the time and dribble fuel in at the end (after the pump shuts off) until you have nice green diesel right up to the top of the filler neck and then watch for a minute to make sure it does not go down. That way you KNOW the tank is full. Every time. I can get 3 more gallons in my 5000TD after the pump shuts off. I had a Ford Tempo diesel that would take another 6 gallons after the pump shut off. Rabbits will usually take another 1.5 gallons when the pump shuts off.

In case some of you haven't figured it out yet, foaming is the culprit. Different pumps and varying temps drastically effect how much fuel a tank will take before the pump shuts off. This is what causes most of the wild mileage claims. In a small tank just a gallon difference makes a huge difference in calculated mileage.

FWIW I have been tracking mileage in diesel Rabbits, Fords, Audis and Volvos that I have had my hands on since 1986 (yes, I am compulsive) and check mileage EVERY tank and on my Ranger TDs I plug the numbers into an Excell spread sheet, so I KNOW what kind of mileage my stuff gets. Any good diesel Rabbit should get 48 mpg combined if you drive it reasonably. I have owned over 2 dozen in the last couple of decades. If it won't, find out why. These cars get the big numbers by cruising in that "sweet spot" that uses almost no fuel. Pushing on the loud pedal mostly just makes more noise and eats fuel on a stocker. Me? I am cheap and don't mind driving like an old man (partly because I am), but mainly because it REALLY makes me smile to do the math on the back of the fuel receipt.

Caveat: All of my numbers come from pretty much stock rigs with cam and IP timing changes along with adjustments of the flow screw. If I do not have to part with the Audi I will start with the more esoteric upgrades like synthetic trans lubes, lowering and bigger exhaust. (Yes, straight up cam timing is not always the best)

[92EcoDiesel Jetta]

There is a spring loaded filler neck vent that you need to depress to let the air out and get more fuel in. Next time you fill up try this: when the filler neck is full, depress that vent and you'll hear a swoosh of air and the fuel level will drop, put more fuel in, then push the vent again and keep doing that until you get no more swoosh and the neck is full. It is also important to fill up at the same ambient and tank fuel temperature since fuel expands when heated. As you drive, the hot fuel returned to the tank heats the tank.

E.g. Immediately after you have driven straight for 500 miles, fuel temp in the tank is much higher than if you wait to let it cool off over night before you fill up.  There will be a difference in how much fuel you can put in depending on tank temperature.

[Toby]

Diesels do not have the flapper valve in the filler neck. That is an unleaded gas car feature to prevent using the old, larger, leaded gas nozzle into the filler neck. The flapper valve is supposed to make fueling with the wrong pump impossible. If I were you I would cut that entire restrictor out since it is not required on a diesel and really slows fill ups. Yours must be a conversion.

[rabbitman]

Diesels do not have the flapper valve in the filler neck. That is an unleaded gas car feature to prevent using the old, larger, leaded gas nozzle into the filler neck. The flapper valve is supposed to make fueling with the wrong pump impossible. If I were you I would cut that entire restrictor out since it is not required on a diesel and really slows fill ups. Yours must be a conversion.

I think he's talkin' about that little "button" sticking into the neck a couple inches down.

My rabbit takes 2 gallons after the pump shuts off, sometimes it's 1.9 and sometimes 2.1 gallons more but it's very consistent. Yup, telling people about my "upper 40's" mileage is very fun........

[Toby]

What vintage cars are we talking about? I have never seen any kind if spring loaded vent on any diesel VW that I have owned. Most of mine have been older stuff though.