Ok,

Im sure there are going to be alot of doubters, but here are the Facts...

When I first got my Disco, I was anxious to find out what the milage was, so I filled it up and then drove it for about 150 miles (gauge said that I had used just over 1/4 tank) then filled it up and did the math.... 17 mpg! I was stoked.

During this time I discovered the forums and read about using Sea Foam, so with that fillup I added the Seafoam and drove it till the light came on, 11 mpg! Talk about a dissapointment!!

I figured that my first calculations must have been mistaken after reading that this was about average for a Disco I, and 12 is what is posted online for the fuel milage of this model..

I have since been just filling it up and running it empty and checking the mileage and it allways hovers around 11 or 12 mpg, but I also noticed that I would get like 200 miles before I would reach 1/2 tank, and then the gauge would move faster and I would only get maybee 250 miles out of the tank.

I was curious if the gauge was just nor accurately reflecting the amount of fuel in the tank, so today when I looked down and had gone 130 miles and used only 1/4 tank of gas I filled it up to check.. Did the math and vwalla!!! 18.6 MPG!!!!

So twice I have filled it up after using only the first 1/4 tank and twice I have had exceptional MPG!!!

The question I pose is why?? I think it has something to do with the the fact that every time I run the tank till the light comes on I get a TREMENDOUS Vacuum when I open the tank. I even started to fill the car recently, noticed that the gas had ethenol and changed my mind and stopped filling after 4 gallons, drove to another gas station and when I opened the tank again, the same TREMENDOUS VACUUM!! I had only driven 5 miles, and the vacum was very strong, when I opened the tank after burning only 1/4 tank, not so much of a vacuum.

So the question is?? What would create the Vacuum and effect my MPG??

 

HA!!
Your gas tank has not been replaced under the recall that was posted back in...'96?
If you were to fill it up and then hit the expressway and drive nonstop the engine would quite after 250 miles or so.
There was a recall on the gas tanks because they didnt vent properly and as the tank got empty there would be a big vacuum and eventually the fuel pump would stop pumping.
Drive for a short time, shut it off and air creeps back into the gas tank, drive for a long time non stop and you run out of gas.
Your one owner only drove it to church on Sundays truck was never fixed under the recall.
Call the dealer with your VIN# and see if it has been done, I am betting not.
Not sure if they will replace it for you for free or not, you are not the original owner and it has been a few years.

 

They will do it... But they want to keep it for 3 days.. this wont work for me as its my Daily Driver!! It creates a vacuum even after a short drive when the tank is near empty, does this correspond with the recall??

 

Yes it does, and unless you want to burn up your fuel pump you will figure something out so they can fix it for you.
Take a long weekend or something.
I know it is your work truck but it needs to be fixed as it will only get worse and then you will be stranded on your way to a job.

 

hey on the recall what year does it end because we have a 99

 

It was only with DI's and RRC's.
I do not know what years it covers.

 

Pancho- for mileage calculations, fill it up and reset the trip gauge. Then fill up next time and divide the miles driven by the gallons to fill up. Don't just go by the gauge, it isn't accurate. I actually use my GPS for miles driven, as the odometer is off by 4%. Take the average of 3 fill ups, and that should be your mileage.

 

Yes this how I did the math.. Gallons in the tank vs miles driven

I can balance a checkbook and do long division as well

I think yoy are missing the point that beyond all logic I get better milage when the tank is nearly full than when the tank is nearly empty...Trying to figure out how I can live without it for 3-4 days

 

I understand what you’re asking. My others vehicles will do the same. For the first half tank the gauge will start off moving very slowly which makes me think "wow, I'm going to get excellent MPG" Usually about the 1/2 tank range, the gauge will move quicker. And for the last 1/4 tank the gauge moves even faster. Regardless of how fast the gauge moves from full to empty, I'm usually satisfied with the total MPG. Again, I'm talking about my other vehicles and not the LR.

My daily driver is a 4.3L V6 Chevy truck. I've done the same calculation that you have done (miles driven by gallons used) and I get about 20+/- MPG. I also do mostly highway driving at 65mph. You bring up an interesting point, why are you getting better mileage at 3/4 tank compared to when the tank reaches 1/4 capacity? Even though I usually only fill up when I'm empty, I will try your method on my daily driver. Fill up at 3/4 tank, and then calculate my MPG.

To get back to your tremendous vacuum sound when opening the gas cap, I've always associated that with a properly working fuel EVAP system. If there was no vacuum sound, that usually indicates there's a leak in the fuel evap system. On newer OBD II vehicles, a loose fuel cap (i.e. leak in system) can cause the CEL to come on. So having a vacuum sound is a good thing.

The recall or TSB that LR had back in the days for fuel tanks not venting on long distance drives doesn't make sense to me. I'm not saying that the tanks weren't faulty; I'm saying why would a tank that's not venting cause your fuel pump to stop working? Again, a vacuum sound is not necessarily a bad thing.

The way the fuel evap. system normally works is that the charcoal canister will store the fumes from the tank until it's sent into the air intake pipe to be burnt in the cylinder. Of course there are all types of switches, sensors and check valves that make this happen.

 

Here is a thought on the fill up. When you fill the tank you are also filling the filler tube a little and also filling the tank past where the pump registers as full. So as you are driving you are burning fuel that does not show on the gauge until it really starts to drop past where the pump recognizes as the full mark. So when you do the math you are only covering a samll amount of miles with a little fuel that looks like the gauge is moving slower. I am just trying to think of an explanation.

Doing the average over multiple fill ups is the best. I use my GPS for calculating the miles since my odometer is off a little too. I average about 13.5mpg of combined city and highway, I am a 94' too. Now my 97'RR runs an average 16.2mpg for combined. I attribute a lot for the fact that I run Mud tires on the Disco and street tires on the RR.