Anything on 2000 Daewoo Nubira [2.0L D-Tech engine]

not good MPG for 4 cylinder engine [26-28 MPG]
Automatic Transmission is sluggish
rust-like substance exterior doors on side-panels

What?

True.
True.
D. None of the above.

Unfortunately, Daewoo’s cars were never exactly the pinnacle of automotive engineering excellence when they were new. After 11 years of use, things don’t improve.

Even Daewoo’s smallest car, which is now marketed as the Chevy Aveo, does not get the type of gas mileage that a car with such a small, low-powered engine should get. So, it is very likely that you will never be able to equal the gas mileage of similar-size cars from the likes of Toyota, Honda, Nissan, etc.

If you are experiencing transmission problems, the first question would be–How often have you changed the transmission fluid? If the answer is never, then a “sluggish” transmission is likely to be an indicator of impending trans failure. When trans fluid is not changed every 3 years or 30k miles (whichever comes first), trans failure can take place any time after 90k miles, and is pretty much of a sure thing after 125k miles.

That being said, the first step is to check the trans fluid’s level, color, and odor.
If it is any color other than red, and/or if it has a “burnt” smell, then your transmission is going to fail soon, and installing a rebuilt trans would cost more than the book value of the car.

If you are very lucky, you may find a normal color and odor, and just find that the level of the trans fluid is low. In that case, refill (slowly, frequently checking the level after adding a small amount of fluid) with the correct spec fluid and then monitor the level every couple of days to see if it drops. Since trans fluid does not evaporate, a low level indicates a leak somewhere, and the sooner it is located and repaired, the better your chances of getting a few more miles out of the car.

As to the “rust-like” substance on the body of the car–Is it rust, or is it some type of dirt/grime?
If there is a lot of visible rust on the body of the car, there is probably 20 times more rust on the chassis of the car where you can’t readily see it.

Since this is a unit-body car, rust damage to the chassis causes significant weakening of the overall structure of the car, and that can be a safety issue in the event of a collision. I would suggest that you have the car put up on a lift in order to assess the extent of the rust on the undercarriage.

If the car needs a new/rebuilt transmission and/or your mechanic finds evidence of extensive rust on the undercarriage, it is time to start shopping for a replacement vehicle, as an 11 year old Daewoo is not worth spending any more than a few hundred dollars for repairs.