Mercedes boss Toto Wolff says an engine degradation issue diagnosed on Lewis Hamilton's unit led the Brackley squad to add a new ICE to the Briton's pool of hardware.
The odds of Mercedes fitting a fresh engine to Hamilton's W12 increased in last weekend in Mexico City. While the change was seen as a strategic possibility to safeguard the Briton against a potentially ruinous DNF, Wolff revealed that principal motivation for the move.
"We feel that we can score more points," the Austrian told Sky Sports F1.
"We have deg [degradation] on the engine that, until the end of the season, is just going to continue to decrease in power. And we haven't yet realised why that is, we're just seeing it creep down."
The change is Hamilton's second this season after the Britain's engine swap in Turkey the yielded a 10-place grid penalty. It also leaves the Briton with just two engines to battle title rival Max Verstappen until the end of the season.
"Just the new one, and the current one," Wolff explained. "I think this is the final one that we need to take."
Wolff added that an analysis of telemetry data had revealed the engine degradation issue, although the Mercedes boss insisted that a certain amount of deterioration is normal.
"Without going into specifics, every engine is degrading," he explained.
"We have seen that over the past years that over 1000 kilometres, there is a certain amount of kilowatts that the engine is degrading.
"Ours is just degrading much more than the average of the past few years and that increases from weekend to weekend.
"So, if we keep the engine, we are, for sure, not going to be competitive in Saudi Arabia and Abu Dhabi."
Hamilton will be sent back five places on Sunday's Sao Paulo GP grid from wherever he qualifies. Wolff said that Mercedes' simulation validated Interlagos is the right venue to undertake the engine change.
Despite the relative setback, the Austrian is nevertheless hopeful of securing a good result in Brazil.
"I think we started on the wrong foot right at the beginning of the session," Wolff said.
"The Red Bulls haven't run at the end, but we have more performance to come that we know we have in the pocket. It's not as bad as it has looked at the beginning of the session."
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