I filled my 89 integra the other day and notice it is only getting about 18-20mpg city/highway combined. Is there something im missing , i thought this would get 30mpg easily, runs fine, changed plugs and air filter. I run 87 octane does that matter? idles smooth and runs good. the temp gauge usually heats up if im sitting but while driving it barely reaches the 1/4 up area. Would the cool temp have that much affect on mpg, it the thermostat hard to replace if thats the problem or do most of your cars run real cool in the winter.

Thanks