The Italian outfit made the change this morning when the official window in which teams are allowed to work on their cars ahead of the race finally opened.
"This is a completely precautionary step," said the team, "the engine, used by Felipe up to the qualifying session yesterday afternoon showed some abnormal parameters, but can still be used on the track, according to the applicable rules, during free practice sessions."
Referring to the Spaniard's car, they added: "Caution can never be enough, especially at the first race. That's why the Scuderia decided to also replace the engine in (Alonso's) car after abnormalities appeared during the usual routine check this morning, similar to those found in Felipe's engine yesterday."
The mechanics are working to complete the replacements, which will not lead to sanctions for either driver, who will start from the second and third positions on the grid.