Means nothing. Compare yours doing the same journey with and without OD. ----- Original Message ----- > Dads 1978 MGB got 28-31 MPG @ 70 mph on extended trips. It had no > overdrive and ran all day at 4000 rpm (or more, I don't remember the > exact figure). > > My 1975 MGB gets 26-30 MPG on the same trips. It has overdrive and > runs at say 3500 rpm.