Wasn't Voyager 1 gaining speed?

The Voyagers, Pioneers 10 & 11, and New Horizons are all in independent orbits around the gravitational center of the Milky Way galaxy, just like Sol (a.k.a., the Sun). read more

It was gaining speed for sometime when it was slingshotting around gas giants like Jupiter and Saturn. But after that the speed of Voyager probes (both 1 & 2) is continuously decreasing. They are just moving through empty space now and if there is something they are encountering right now is only in the form of resistance to their motion. read more

Even though most of the launch vehicle's 700 ton weight is due to rocket fuel, Voyager 2's great travel distance of 7.1 billion km (4.4 billion mi) from launch to Neptune resultsed in a fuel economy of about 13,000 km per liter (30,000 mi per gallon). read more