Daniel Ricciardo admits his Red Bull team couldn't explain what he called the "fundamental" problem with his Renault power unit which caused him to retire for the second straight weekend in Mexico.
The Australian had a torrid Sunday at the Autodromo Hermanos Rodriguez which began with his power unit from Saturday being changed after concerns it would not last the race, resulting in a grid penalty which dropped him to the back of the grid.
His new engine would last just six laps, however, before the Red Bull driver had to pull into the pits with an MGU-H failure, becoming the first of four drivers using the French manufacturer's engine not to make the finish.
“Certainly something fundamental [is] going on,” Ricciardo claimed afterwards. "We've been coming to Mexico the past few years so there shouldn't be any surprises - I know the altitude and temperatures have been hard to stay on top of this weekend.
"I don't know if it's this year's spec of engine, which is struggling up here - obviously it is, but why we're not sure."
On the fact problems struck a number of drivers using the same engine, he added: "It's been a pretty grim weekend for a few of us, it's a shame to be out early again. I guess it's a bit of what Max [Verstappen] experienced early in the year - it's not so fun."
Ironically, it would be his teammate who went on to win the race in Mexico by some 20 seconds over the Mercedes of Valtteri Bottas, but, despite a good start, there would be very little for Ricciardo to cheer about and also leaves him in limbo heading into the next race.
"Obviously the weekend's turned to crap," he said in summary. "I did what I could at the start - it was pretty close, there was a bit going on - but I made quick progress. I told Helmut [Marko] this morning that I'd get up to seventh by the end of the first lap. I was a couple of laps off I think, but we got close.
"We put the new unit in, but something went wrong. Not really sure what it was or where that puts us for Brazil," he claimed on whether he'll take yet another penalty at Interlagos.
