Daniel Ricciardo and Nico Hulkenberg plus McLaren's Carlos Sainz Jr have reverted to Renault's Spec B engine despite taking Belgian Grand Prix grid penalties for an upgraded power unit.
All three drivers have taken five-place grid drops for having run with an upgraded spec C in Friday practice.
But despite the engine's reliability and performance improvements, Renault and McLaren removed the power units and fitted the cars with Spec B versions overnight.
Renault said the change is not because of reliability concerns but instead because it wanted to get the new power units into its race pool.
"The plan is to take penalties at a track where there is a possibility to overtake, while entering a needed extra ICE [internal combustion engine] into our pool for the rest of the year," said a Renault spokesperson.
McLaren concurred that its change was about better managing engine mileage over the remainder of the campaign.
Overtaking at the next races at Monza and Singapore is much more difficult than at Spa, so introducing a new engine there would likely be more costly.