There was a time, not so long ago, that my 1991 Civic DX got an average of 40 miles to the gallon. On my last full tank I got just over 100 miles. The spark plugs were recently replaced, along with the air filter, fuel filter, plug wires, distributor, and some other things I can't remember off the top of my head. I live in the mountains, and the temperature hasn't been above freezing for about a month. It gets to around -30 F every night lately, and rarely gets above 10 F. My car hasn't seen any action lately besides the mile-or-so drive to work and back, so it never really warms up. I know cold weather reduces milage but I'm wondering if that's all the problem is or if there's something else wrong.

Thanks.

 

Sounds like you may need to replace the thermostat. If you drive for 10-15 minutes, does the engine reach full operating temp and the heater works?

 

Just a recommendation... if you have typical honda rust, you might think about inspecting your gas tank and fuel lines. I had a similar problem a few years ago and my tank turned out to be rusted almost completely in half. Had to replace it and the fuel lines. Hope that's not your issue.

 

check tire pressure.
someone stealing your gas?