The Outdoor Girls in a Motor Car - Laura Lee Hope

In "The Outdoor Girls in a Motor Car, Or The Haunted Mansion of Shadow Valley", one of the girls has learned to run a big motor car and she invites the club to go on a tour to visit some distant relatives. On the way they stop at a deserted mansion and make a surprising discovery.

This is the third book in the "Outdoor Girls" series. (Summary from an old book advertisement)