Volvo 1988 740 GLE Low gas mileage.

You are stumbling around changing parts with no real idea of what the problem is. You still have the chance to save yourself some money. Just take the car to a mechanic with the proper diagnostic equipment and let them find the cause of the problem and fix it.

What engine and transmission do you have ? What kind of mileage are you expecting ? You stated " It does something like 18mpg or so in the city and around 23mpg or so on the highway." How did you arrive at these figures ? The only way to accurately figure fuel mileage is to divide miles travelled by the amount of fuel used. You need to do this over several tanks of gas to get an average.

The engine is the B230F. It is a 8valve nonTurbo. I don't have the Automatic Transmission exact model.

I did that for the highway miles. I took to around 5 Long road trips (1200 miles per trip). And that is how I computed the mileage for the highway. I did it similarly for the city driving.

You are actually right. I want to do that but the problem is sometimes if you go to some mechanics they would just rip you off to make money and I try to minimize that rip off as much as possible. I was wondering if my concern is real or it is just fine as it is. I am not really sure.

I have seen a manual transmission 1989 Volvo 740 GL do on the highway something like 28 or 27 mpg according to a mechanically savvy friend. Is that difference is only attributed for the difference in transimission only. I don't know?

I will probably get it to the nearest dealer? Or known Volvo mechanic?

EPA mileage figures for your car are 22 city, 28 highway so your mileage figures look a little low. You say the car is running very rich, how can you tell ? Have you checked coolant temp sensor ? If the sensor has failed and is telling the computer that the engine is colder than it actually is your mileage will be low. You also need to make sure the thermostat is working properly or the engine may never fully warm up which will also cause it to run rich.

There are many factors which affect fuel economy. Tire pressure, engine tune, engine condition, high speeds, heavy traffic, etc..... will also cause a reduction in mileage. Any decent mechanic should be able to check your car over for any problems that may cause reduced mileage. One other thought, cheap gas from cut rate stations can also cause a substantial reduction in mileage.