The 1986 Castrol 500 was an endurance race for cars complying with CAMS Touring Car regulations, which were based on FIA Group A rules. The event was staged on 14 September 1986 over 129 laps of the 3.9 km Sandown International Motor Racing Circuit in Victoria, Australia, a total distance of 503 km. The race, which was Round 3 of both the 1986 Australian Endurance Championship and the 1986 Australian Manufacturers' Championship, was the 21st "Sandown 500" endurance race.

The Sandown 500 is an annual endurance motor race which is staged at the Sandown Raceway, near Melbourne, Victoria, Australia from 1964. The event's name, distance – and the category of cars competing in it – has varied widely throughout its history. Most recently, the event was held as a championship event for Supercars from 2003 to 2007 and from 2012 to 2019.