Am I getting the right MPGs?

[Young Whitey]

The car is a 94 Olds Ciera with 3100, 4T60E, and 147K mi. Original and stock eng/trans. For the past few tanks of 90% highway (70-80mph) Ive been between 20.5-21.7 MPG. I feel like I should be around 25 though.

The only 'mods' are KYB shocks and Lumina 16" rims with 225/50's. So I think I might be going a little faster/traveling a little farther than the instruments indicate.

The other thing that is affecting the MPGs slightly is when the trans gets hot it wont go into OD. This doesnt happen too often especially in the winter though.

Since I got the car a little over a year ago I did the usual maintenance like plugs wires filters cleaned the MAF, etc, so the car is maintained and runs real good and smooth.

The car is pretty much empty, cargo is usually me plus a bag and maybe an 80lb dog. I dont let it idle long, I just get in and go.

What are you guys getting for mileage? Any suggestions on things I could check out?

[tractorman]

In its younger days, my '94 Corsica (same engine and trans. as yours) would get about 29-30 on the highway. The fuel mileage gradually went down until at I was getting about 25 mpg on the highway- I noticed this at around 130,000 miles. At 140,000 miles, I replaced the oxygen sensor because I suspected it might be the problem, and the car immediately strated getting about 28 mpg. It's now at about 157,000 and still gets 28.

[Young Whitey]

Hmmm, Im not throwing any codes but Its worth a try, especially for a jump in MPG like that. I actually have a wideband o2 sensor left over from my WRX days, but I dont think it would be worth it to weld another bung in just to see whats going on. I will try a new o2 sensor. I just looked it up, a new one is between $50-$80 at autozone. I would be real happy if I could get 28-29 on the highway.

[Young Whitey]

I wonder if a high flow cat and maybe a free-er flowing muffler would make much of a difference. I assume my cat is original. I wouldnt want it to be loud though.

[nixtux]

My 1995 Cutlass Supreme averages around 29MPG@70MPH / 18MPG in town --- completely stock /w bad air filter and old ass fuel filter in the summer /w A/C on high. In Minnesota nonetheless --- so it's always f'n up here. I must admit I didn't take very good care of the car. But since I started renting a house /w a huge garage I've found myself spending a a couple hours a day working on it. At least when it's above 20F.

I've since replaced the air/fuel filter so once I get the motor and transmission back in I'll post new numbers.

The motor has 176,000mi but was rebuilt around 110,000mi ago.