1995 Mercury Sable GS -- Overdrive Transmission

Hello,

My girlfriend has a 1995 Mercury Sable GS with Overdrive Transmission.

We don't use overdrive around town because we have both heard people
say using it for town (stop and go) driving stresses it and to only use
it on the freeway and on long trips.

I have also heard it is ok to use Overdrive around town.

I am curious if anyone has an opinion on whether it is ok to use the
overdrive in town driving.


Also anyone know will we get better gas milage using overdrive on long
trips wheere we are on the interstate for hours at a time.

As an aside note.... any opinions if Fuel additives like HEAT and the
like as well as using premium grade unleaded fuel help much...?

We are going on an approx 800 mile trip in a few days. I want to
maximize Fuel effenciency.


Thank you