McLaughlin and Mostert were again 1-2 in practice.
Mika Hakkinen has acknowledged rumours linking his protege Valtteri Bottas with McLaren.
Weeks after the rumours first emerged, Ferrari has this week finally admitted that engine boss Luca Marmorini is leaving the Italian team.
Longtime Honda/Acura racer Peter Cunningham is behind the wheel.
Pietro Fittipaldi continues to go from strength to strength, extending his championship lead to 36 with 238 points.
Drivers include Bob Motz and his jet-powered semi.
No longer has to share space with Elan Motorsports Technologies.
Volkswagen and the Polo R WRC clinch all four fastest times