Hey guys

I've been noticing I only get about 150 miles out of a tank of gas lately. I remember getting about 180 miles per tank during the summer, and my driving route/style hasn't changed . My lt1 run extremely well and idles smoothly, although it hasn't had a tune up on about 50k miles. I was wondering what the average LT1 (only boltons and 93 octane gas) MPG would be for mixed city/ highway driving.

Thanks.

 

Winter blend gas. Higher evaporation rate than Summer blend, and burns quicker. I deal with the same issue in my Suburban. 15mpg during summer and no AC, roughly 13.5 winter.

I don't drive the TA in the winter.

 

I can do 17 with some spirited driving in town and 22-23 mpg which is over 300 miles per tank on the highway with the mods i have... id say you need a tune up to start with...
o2's all workin right?

 

Assuming you are using the whole tank (~15 gallons) those numbers are absolutely horrible for a stock / light bolton LT1. We are talking 10-12 MPG.

Do you floor it at every red light? Are you in a very dense are where you have lights/stop signs every 5 feet? Huge hills?

You should be seeing somewhere around 15 city and 25 highway in a auto car. Any signs of the car running rich? (burnt fuel smell, black smoke out of tips, etc.)

 

My o2's are new.

I mainly drive short trips to school which are mainly back roads with a lot of stop signs and hills (I live in a hilly area of PA).

I literally baby the car, too. I have floored it literally one time. I drive under 3000 rpm.

 

I drive 17 miles to work, all highway, and I barely eek out 18mpg. Its just where you live, hills and lights kill gas mileage. Get a tune up. Even if the gas mileage stays the same, its piece of mind and the car will feel better.

Also noticed, no matter if I drive like a teenager or a grandma, gas mileage doesn't change much for me.

 

You would get a better idea of the car's actual performance if you accurately calculate the "miles per gallon", rather than using a crude measure like "miles per tank".

In any case, even with all the possible negative factors that reduce fuel mileage, getting (apparently) 10-12 MPG is indicative of a problem. Even the 12-14 you indicate you got earlier isn't very good.

Engine would appear to need some serious attention.

 

I suspect I may need a new exhaust manifold gasket. The engine runs too well for it to need plugs and wires.

I was quoted $1300 for a full tuneup, including cap and rotor.

Vacuum leak possible?

 

Your idle would probably be high if that were the case.

Can you scan the car? Maybe the car has something preventing it from getting in to closed loop (had an O2 sensor do that to me).

 

What would you consider a "high" idle? When the engine is warm it idles around 700rpm.

 

Crappy gas, but make sure your tuneup is healthy and O2 sensors aren't too ancient.

 

650 in park, 550 in drive. I would consider 700 normal. Something like 800+ in drive would be a high idle.

 

Fred mentioned something "more serious" could be wrong with my engine. Could it be possible that I have a blown head gasket? There is brown/ milky condensation on my oil filler cap. I was told short drives can also cause this, as I only drive 10 mile round trips to and from school. My car does NOT overheat (stays at about 180 degrees) and my coolant is not low.

I'll post some pictures.

What do you guys think?

 

 

Sickening. I'd clean that filler neck immediately. Just gross to look at.