FI cleaner temporarily worsens mileage?

I have a 2001 Honda Civic HX (1.7L VTEC-e). I typically average ~42 mpg. I recently used Techron in two tanks of gas in a row. For those two tankfuls, I averaged 38.5 mpg. After the Techron had run through, the average for the next tank was back up to ~42 mpg. I concede this may have been a coincidence due to unaccounted variables.

My question is this: has anyone heard of Techron decreasing mileage in the short run? [The engine was running fine; I used the Techron hoping to address erratic fuel gauge readings.]

I concede this may have been a coincidence due to unaccounted variables.

That is likely it. It is not impossible that something is related to the additive but less likely IMO.

BTW why did you use the additive? That could be the answer.

Techron will have no effect, positive or negative, on your fuel gauge reading.

I doubt it had any effect on mileage, either. Most likely a coincidence.

Techron is unlikely to affect your mileage and will certainly not cure erratic fuel gauge readings. If your car is running well and you have seen negative effects when Techron is added, why, don’t use it again!

Actually, the “benefits of use” list on the Techron label mentions correcting fuel gauge problems by cleaning a stuck sending unit. Of course, it’s listed last. I don’t have a Techron bottle in front of me to check the exact text, but the phrases Chevron uses on its website are “Cleans sulfur deposits from gas gauge sensors” and “Protects gas gauge sensors from malfunctioning.”

I just thought I’d give Techron a try, and incidentally noticed a drop in mpg for just those two tankfuls.

The gauge issue is this: the needle drops to near the “empty” tick and the low fuel light comes on w/ ~ 3 gallons remaining. After a few miles, the needle rises back up above E and the light goes out. Eventually, the needle comes back down and the light engages again. The problem is, with a shared car, a driver can’t be sure if this “buy gas now” indication is the first (a false alarm) or the second (“no, really, buy gas now”).

I’ve found a few Civic forum threads describing the same issue written by people who bought their Civics new. Early on, Honda replaced gauge clusters under warranty, but eventually changed strategy to describing this gauge behavior as not a bug, but a feature.