I was wondering if anyone could help me find a reason why my 2000 3.8l gets horrible gas mileage. I can only go about 200 maybe 250 miles on a full tank of gas? Shouldnt i be able to drive alot farther?

 

Sounds like you have a vaccuum leak or even a leaking manifold gasket. Or even an o2 sensor going bad. Possibly a fuel injector as well. Those are the typical causes of poor mileage.

 

I get about that when I am not so nice to the right hand petal. When I am good to her I get about 280 to the sniff point.

Massey

 

How many miles on the car, and how many miles since you last replaced O2 Sensors, plugs & wires? Also, upgrading with a better flowing cat-back and CAI should help your mileage, assuming no lead-foot...

 

First Question I would have is what are you calling a full tank of gas. I just checked the owners manual and it says the tank in my 1999 is 16.8 gallons. I filled it up two days ago after running 20 miles past the point the the Check Gauge light came on and it only took 13.5 gallons til the pump shut off and that was the most gas I have ever put in it.
I have done the math over three tanks and I averaged about 21.5 mpg. So on 13.5 gallon fill up I go about 290 miles.
I also have the original window sticker to mine and it is rated at 19 city 29 highway and I have to say I do not have any clue how that 29 could be achieved. I went on a trip one day that was right at 240 miles with 225 of that on the interstate. I went 65mph or less that entire trip just to see how good I could do and I only averaged 24.5mpg
In the end you need to track your gallons and mileage over about three tanks and do the math and see what you get because depending on what you are calling a tank 250 miles aint that bad.
I can also tell you this my wife has a 2011 5th gen v6 and her gas mileage is no better than my 99

 

According to my owners manual, my 1994 has a 15.5 gallon tank but somehow, I'm able to put 17.2-17.5 gallons in it at the pump when it's on empty.

 

What type of driving do you do? I drive about 90% highway and for the first time averaged over 30 MPG across a tank last week. I have hit 29.5 a few times before. If I get caught in a traffic jam the mileage falls off very quickly or if I have to run around in town it will drop also.

If you have no other syptoms and all your maintenance is up to date you may want to replace your O2 sensors. You really want to be sure the car is in good running order before you replace the O2 senors. They are not cheap and will fail pretty quickly is there is something else wrong with the car.

 

I am pretty sure your gas station is ripping you off. I ran out of gas and had to get a tow once (ya I know) and one other time I costed into the station (second time was not my fault, 3 hour traffic jam) Both times I was able to get a little over 15 gallons om the tank. The spec from GM is 15.5 on the camaro until 1999 when it went to 16.8. If you told me you got a half a gallon over I would believe that but 2 gallons??

 

Yeah that's what I thought too. The pumps were inspected a week later because I reported it and they checked out to be fine. Also if I fill it that much it smells like gasoline in my car for about a week. This all started right after I replaced my fuel pump.

 

If you smell gas after you fill up that is a good sign that you didnt get the seal on the tank on right. OBDII cars will pop a CEL over that.

The absolute best I have ever done on a tank of gas was 32MPG on an all freeway run. IT was about 4 hours, no traffic and 70 the entire way. I was really happy. Now in town driving I get low 20s if I am nice and high teens if I play rough. I am pretty happy all and all with the mileage I get, this is the most efficient vehicle I have ever owned. Hell I was happy when my Avalanche was getting 22 on long freeway runs.

Massey