I have been driving my 91 Accord LX wagon for the past 3 weeks now and my gas mileage doesn't seem to be as good as I was expecting. It has 232k miles and is an automatic. I run the tires at 35 psi and I have replaced plugs, pcv, air filter, cleaned out the iac valve and ran a can of seafoam through a tank of gas. I also installed a brand new radiator and t-stat due to a leak. The best I have gotten was 24.7 driving 65 - and the worst was around 21 but so far the average is around 22.5 mpg. Is there a speed or RPM that this thing does better? I drive around 60 for the last tank and only got 22.2? Should I try driving faster for a tank and see what happens? I was hoping for at least 25 mpg consistently - maybe unrealistic? By the way I live in MN and temps have been 5-30 degrees. Thanks!

 

I usually average 350-400 miles on a tank and about 27mpg. I dont accelerate real fast and try use my cruise control, etc. Mine is a coupe though so its a little lighter and I run 32 psion tires. Did you check your O2 sensor?

 

What is there to check on an o2 sensor? There is no code so shouldn't it be okay? How much of a difference will there be between a coupe/sedan/wagon on mpg?

 

Something else to consider; in the northern climates the gasoline suppliers throw in different additives during the winter months.
The ECT will tell the computer to richen the fuel mixture when running a colder engine, and there are car warm up times thrown into the whole equation.

 

I know they say that winter gas can yeild a couple less mpg - I suppose that isn't helping. Here in MN we always have ethanol blended into the gas but in the winter I think there is even more. Even with that though I was hoping for 25 regularly. Since this car is warmed up within a couple miles of driving I try not to let it sit and warm up for long - if at all.

 

I live in MN too and you should be getting better mpg than that.

 

That's what I was thinking too. The quest continues....

 

You've checked lots of the obvious stuff. How about a compression check? When you changed sparkplugs, what did the old ones look like? How about dragging brakes or wheel alignment?

 

Plugs looked great - but they were gapped way to big (at least double what it should have been!)and a little old. The color was good and there was no sign of oil or anything. Compression on all 4 cylinders was 185.I think therear brakes need some work but I don't think they arehung up or anything - the frontshave new pads and seem to be good as well. It does need an alignment so maybe I will check into that too.

Will the dealer have the EGR plugremoval kit?

I drove 100 miles of mixed drivingyesterday and did 24.4 mpgso maybe things are getting a little better?

 

Compression sounds OK. How much driving since replacing the plugs? Reading your post it isn't clear whether the bad mileage is entirely after the new plugs?

How about plug wires & distributor cap/rotor? Start the engine cold after dark, turn off all the lights, & look for arcing (blue glow)along the wires & cap. Any arcing means it's probably doing some misfiring.

Alignment problems will wear tires funny. But it takes energy togrind away at the tires likethat...

What can go wrong with an auto-tranny after 230k miles? (LOL...)
Iwonder whether something wearing out in the tranny could introduce extra drag?? I'm not very good at autos, mostly own manual trannys.

Cold weather sucks gas especially during warmup. Also it takes more power to drive thru snow & slush, so it depends A LOT on how the roads are cleaned up.

100 miles isn't much for measuring gas mileage. There's a lot of normal variation in how much gas you can put into the tank. Use total miles & total gallons over several consecutivetankfuls to get better accuracy.

Finally, just to add another bizarre idea to the mix... How's the corrosion on the fuel lines under the car? Leaking fuel evaporates slower in winter, so you don't always smell it.