Hi! Hoping I fixed my crx poor mpg
 

I've been getting around 29-31 mpg city and highway on my CRX HF for about a year now and found dirty oil, plugged PCV valve, lazy O2, what i think was dirty injectors and intake manifold, and a thermostat stuck open. I've driven a tank or two after each "fix" with no improvement except when I "cleaned" the injectors with Techron and redline SI-1. I jumped up to solid 41mpg on the redline tank but dropped back to around 30 on the Techron tank. I can't explain that.

Anyway, I just replaced the thermostat so hopefully all the problems are solved and my mpgs will finally come back home. Wish me luck or supernatural skills in finding and fixing further problems. :-)

Also hello everyone! It's great to be here!

I'd say a bad O2 and a stuck open thermostat would be the biggest MPG issues. Hope you get it sorted out.

Welcome to the forum!

Try a higher grade of gasoline?
Change the transmission fluid too, just because it's supposed to be done every other year.
is everything on the engine an exhaust stock?

I actually tried alcohol free gasoline last tank, before discovering the thermostat problem. I paid $0.30 more per gallon and mpg stayed pegged at 30. That's perfectly consistent with running in open loop at all times, which is what a bad thermostat could do.

I also changed transmission fluid a week ago, just because I figured it probably needed to be done. Don't know how old the old fluid was, but it was still so clean, it almost hurt to throw it out. I doubt it was causing any problems.

The whole car is bone stock, no mods whatsoever.

The new thermostat has actually made a noticeable difference in how it drives. It seems smoother, and my heater definitely works better! :) I have a sneaking suspicion I've solved it this time. We'll see on my next refill.