See if you can figure this out... I can't...

92 Civic, original owner.. I've been driving it for 15+ years/190K... gas pump always shut off around 8 gallons and I typically got 320 miles per tank.. 40mpgs..

- Just in last several months, I've still been getting ~320 miles, but has been taking 9 gallons to fill up. 35mpgs..
- I recently added Lucas Fuel Treatment.. to my now 9 gallon fill-up.. I got 376 miles - back to 40mpgs - but now with an extra gallon...
- On the next fill up - 9 gallons, but only got 320 miles... back to ~35mpg...
- I just added Lucas again, we'll see...

1. What could cause the MPG drop?
2. Why am I now adding an extra gallon?

Recently added new same tires/alignment. Plugs/dist.cap/rotor/wires changed just over a year ago. I checked the cap & rotor, looked clean, clean..

Interesting

MPG could drop for a huge array of different reasons. Bad fuel mix, altitude, driving habits, intermittent problem with the civic, etc etc etc

the extra gallon is odd though. Maybe the pump was shutting off early and not giving the 9 gallons originally.

Sounds to me like the Fuel Injectors and/or Fuel Pump might need to be checked.

yeah - it was the added gallon that really got me..

As far as drop in mpg, much of the stuff is original from the factory (injectors, pumps).. So I can expect a loss.. I'm sure its the car, but not sure what to go check... I've tried everying I can think of... Runs great. I've gotten gas in multiple states/counties/companies just in case the pumps/gas seemed outtawhack in a certain county or company...

But ?? on the gallon. 8 always did seem low amount to hold, but it would shut off this way for years... and years...

BTW - I tried the Lucas in the X - still 15 :)

Are injectors an easy thing to check? I will check the Haynes at home - but this never seemed like a DIY...

Didn't know if these were an easy thing to 'pull' to check????

It's something that the fuel system cleaner semed to help, but only while being treated... I'll assume the extra gallon is something unrelated..

have you changed the fuel filter?

Your fuel level sending unit may be acting up. You may be dipping into your tank's reserve even though your gauge is not showing completely empty. Had a Chevy truck that did this. I don't know if that's it for sure, just a thought though.

:) no, never changed fuel filter. I know is really bad, but I hate dealing with the banjo nut kind of fuel filters.... 190K isn't that bad on a fuel filter, is it? (lol.. i know...)

I really figured that a bad fuel filter would prevent fuel from flowing... but not cause me to burn more... But I really don't know. I need to change anyways.... will see if that helps.

I got ~40mpg on this last tank with the fuel treatment again. So I can't figure out what would cause tis that fuel treatment would 'help'..

These are all great suggestions..

Maybe its something to do with ethanol? I only buy gas in VT rather than MA; because MA is very "watered" down, so to speak. Hell, last time I brought my X to the shop because something was wrong they asked me if I had filled up in MA lately.

It will cause a drop in MPG to some degree. 190k on a fuel filter is WAYYYYYYY ovedue. I think honda recommends 60K so your about 3 times past that.

Yep, I figure 50,000 - 75,000 miles is a good interval for Honda OEM fuel filters. They are large and very well made but still can get clogged and cause some erratic behavior. But I'm guessing that's not the problem.

For a quick clean-up of injectors, it's hard to beat Red Line Oil SI-1. Try 1 half bottle in about 8 gallons ... then the other half of a bottle for the next 8 gallons. Do this once per year and during a time when you will be starting and stopping often (not a long highway trip) as you want many heat up and cool-down cycles as possible. This stuff is only like $6-8 per bottle and is one of the strongest pour-in detergents on the market.

Other than that, how are the brakes? Any sign one of the calipers is sticking? That will make a massive difference in the fuel economy and may have a sudden onset ... just as you described.

Changed the fuel filter... we'll see how it does. Needed for sure anyways!

I'll have to check on date of brakes - seems not that long ago, but may be close to 2 years. But seem to be working fine. Good call - i'll keep an eye on it. Since the lucas seems to help, but then back to 35 when not in - makes me think in fuel system somewhere.. I'll try the redline!

hmm- harder to find the redline than i thought. may have to get online

pro2amendment, Pep Boys carries the stuff. They are my local source for the 1 bottle I buy each year. Summit Racing carries the stuff as well. I tried to search site-sponsor Rock Auto but could not do a generic search without year/make/model, etc ...

OK - Thanks. I looked everywhere, except Pepboys (figures...) There wasn't one by me. I'll give them a try. I picked up another brand just to try since I needed to fill up. Will try pepboys.

http://www.amazon.com/Line-SI-1-Fuel-System-Cleaner/dp/B000T9RLT0/ref=pd_bbs_10?ie=UTF8&s=automotive&qid=1236535259&sr=8-10

for a case unfortunately

bottles

http://www.amazon.com/Red-Line-SI-1-System-Cleaner/dp/B000J3G8MW/ref=sr_1_4?ie=UTF8&s=automotive&qid=1236535346&sr=8-4