The blaze happened in a lay-by on the A76 near Enterkinfoot, Thornhill at about 9 pm on Friday night. The car, a silver Audi A3, had been parked there for a couple of weeks after breaking down.
Constable Scott Graham said: “Many local people passing this lay-by will have seen this car parked there in the past few weeks. We are treating this fire as suspicious and are keen to hear from anyone who may have seen any suspicious activity around the car over this period, and in particular on Friday evening.”
Anyone with any information can call officers at Thornhill on 101.
