From what I've seen, if the needle is riding E and you put about 3-3.5 gallons in it, it goes to half b/c of the weird tank shape. Specs say it has a 15.5 gallon capacity.

 

Didn't read the entire thread (5 pages lol) but maybe there is a fuel leak?

 

I'm in an 01 so it's a 16.8 tank.

 

Didn't realize til now that this is thread is still alive! I wanted to share a few things with you guys. I realize there are a lot of people on LS1tech that seem to think the LS1 should routinely be getting Toyota Camry gas mileage. However, let's set that aside for a minute and look at some numbers - the actual EPA ratings for our vehicles.

Originally, the window sticker for an M6 LS1 estimated 19 MPG City/28 MPG Highway (I've seen some window stickers that said as high as 30 MPG highway). So, if you are using this as a measuring stick, you are going to have some high expectations. However, the EPA testing methods were flawed - they were performed at a perfect 75 degrees, average city testing speed was 20 MPH, average highway testing speed was 48 MPH. Also, acceleration was very conservative and no accessories (A/C or other) were on. Obviously, this is completely unrealistic - who do you know that averages less than 50 MPH at Highway speeds? The EPA knew this, and people complained. So, in 2008, they changed the methods for testing fuel economy. A/C use was added (13% of the time, at least), along with more aggressive acceleration and much higher testing speeds (as high as 80 MPH highway). They also tested the vehicle at lower temperatures (as low as 20 degrees).

Using this new method, the M6 LS1 F-bodies are rated at 17 MPG City/26 MPG Highway. For automatics, it is 16 MPG City/26 MPG Highway. Keep in mind, the M6 figure is still assuming you are using the ridiculous CAGS (skip shift) system - which of course most of us aren't. Most of us are also probably using the A/C more than 13% of the time, and if not, your windows are probably down (which gives WORSE fuel economy than the A/C, by the way). In addition, most of us don't drive to work on a dyno (which is where the EPA testing takes place), and might encounter a hill or two.

So, in conclusion, getting 14-16 MPG City and 25-27 MPG Highway if you have some bolt ons and/or drive your vehicle aggressively is probably right where it should be. That's just reality, guys. This is an intentionally simplistic 5.7L engine without a ton of computer trickery for added fuel economy. That's what makes these motors so darn reliable and so darn easy to mod. Are there people out there that might see better fuel mileage than that? Sure. But if your car isn't, it just means it's performing as expected.

I'll get off my soap box now - but hopefully some of you will read this and stop trying to chase down phantom "issues" that is keeping your car from making the 22 MPG City/33 MPG Highway that some people on the forums are claiming should be normal.

 

sounds believable. but my phantom is that i get 180/12.5 gals from full to e. its an 01 so 16.8tank. bad sending unit in the tank?

 

14k, I don't think your sending unit is bad - mine does the exact same thing. I have an 02 with the 16.8 gallon tank, just like you. I just filled up tonight - took exactly 13.4 gallons, giving 3.1 MPG left in the tank, and the check gauges light had been on for a few minutes prior. And we aren't the only two that have made comments on here about that. Looks like GM is just being ridiculously conservative - maybe so people don't run out of gas? Annoying though, I agree - because it seems like you get to E so darn quickly lol. 180 miles in 12.5 gallons is about 14.4 MPG. Are you mainly driving in the city? If you do a considerable amount of highway driving, you might have problems. My commute is entirely shifting gears through the city, 0-45 MPH, and a good bit of idling, so I'm sure my 14-16 MPG is where it should be.

 

All city. 55 is the highest ill be at on 1 road for about 2 minutes the. The rest is 40 and stop and go traffic.

 

Oh and my buddy with a 99 ta gets about 230 all city. Wtf lol his car goes 50 miles before it gets off full then about 90 at 3/4 I'm usually at 110 at the 1/2 mark.

 

Gotcha - if you're all city like me, then that fuel economy is totally normal. Sounds exactly like my driving pattern. Wasn't 99 the old smaller fuel tank? Maybe the shape of the tank/sending unit is different which makes the fuel gauge show the level differently. We could both probably drive 230 miles in the city without running out of gas, but it's just that the check gauges light would have been on way before hand. I've pushed it to 200 miles before and think when I filled up, I still had like 2-2.2 gallons left in the tank.

 

I guess I have been chancing a ghost that's not there. Iv been seeing all these people on tech claiming 16-18 in city and ls6427 with his 427 getting 230/tank driving aggressive while I get 180 and I baby my z.

 

in my 98 Z28 A4 110,624 miles (completely stock) except old aftermarket exhaust, I averaged 22.6mpgs mixed city/hwy. I drive relatively aggressive. usually 3500-4000 when I let off and let it shift. every 5th light or so I stop at I romp on it. My last full tank to completely empty I got 366 miles. Mind you I have the steel 15.5 gal tank not the plastic 16.5 gal tank. That's roughly 23.6mpg I always drive with the windows down and the A/C off.

 

I think 98 was the only year with the 15.5 gal tank. 99+ had the 16.5 gal tank.

 

My friend has a 2010 Camaro 2SS/RS 6spd LS3 SLP LM axle-back and he managed 34mpg hwy at 55 in 25*F weather with snow. Just thought I'd share that.

 

I believe that 100%. Especially on an LSX motor 6spd, where your engine is at 1000-1200 rpm at 55. However, the large majority of people don't go 55 - in fact, where I live, you will flat get run off the road if you are going 55. That's why the EPA testing speed has increased so dramatically.

My point is not that these cars are incapable of achieving excellent fuel economy under certain circumstances, because as you have pointed out, that certainly isn't true. My point is this: the expectation some people on LS1tech have that you should be achieving 4 cylinder-like fuel economy in MOST circumstances on a 5.7-6.2L LS engine is just simply not realistic.