Red Bull Racing's split with Renault is done and dusted, but team boss Christian Horner isn't finished dressing down the outfit's former engine partner.
Following a year marked by Red Bull's incessant demands for more performance and better reliability from Renault, with the manufacturer coming up short on both fronts, Horner has called into question the company's true support for its F1 engine programme.
"Credit where credit is due, in Mexico we were provided with an engine that was capable of winning, as we were in Austria and China," Horner told Motorsport.com.
"We were lucky in Monaco, even without an MGU-K. Any other circuit and we would have been stuffed.
"I have total admiration for the Renault guys in the garage that are working their socks off, week in, week out.
"But I think they've ultimately been let down by the main house's lack of commitment to development and reliability."
As Renault dealt with upgrades and changes, Red Bull was left frustrated at times by the lack of availability of specific parts.
"I think too often you see parts being taken from one engine to go onto another," Horner noted.
"That's been too much of a theme over the whole hybrid era, and that must compromise dyno time, that must compromise endurance running, and so on."
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In the latter part of the season, Red Bull was offered the option of running Renault's more performant C-spec engine, a unit the works team had declined to endorse for reliability reasons.
However, Horner insists that specification was used thanks to the optimization work undertaken by the Milton Keynes-based team's fuel partner.
"Exxon have done a very good job for us," said Horner. "Their difficulty and frustration has also been that as a customer we get very limited dyno time.
"But they were able to come up with a fuel that made the C-spec work, and we've managed to get that in the car and run that successfully, when the works team haven't been able to do that. So that's also been encouraging."
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