Hamilton faced "imminent" engine failure in Brazil
Mercedes believed that Lewis Hamilton's engine was about to fail early in the Brazilian Grand Prix before the world champion went on to win.
On lap 28, the Mercedes power unit engineers reported that a failure was "imminent" for Hamilton, due to an exhaust issue that had led to high temperatures.
At the time Hamilton was urgently trying to make up ground after his early pitstop dropped him out of the lead.
"We have the engine guys here in the back, and then we have them back at base," team principal Toto Wolff explained.
"I have about 10 channels open, and what I could hear on the meeting channel was 'Lewis Hamilton, power unit failure imminent. It's going to fail within the next lap'.
"And I put the volume up and said, 'Excuse me, what?' And they said, 'Yeah, we have a massive problem on the power unit, it's going to fail on the next lap'.
"But it didn't fail the next lap, and I said, 'When you guys have a minute, tell me what's happening'.
"'Well, our exhaust is just about to fail, and we're overshooting all the temperature limits'.
"I said, 'So what's the fix?' They started to fix it by turning the whole thing down. The temperatures went down to below 1,000, to 980 degrees. But it's still too high! That was truly horrible."
Wolff admitted that he was surprised that the car finished the race.
"God only knows how you can fix hardware that's just about to break and make the car finish. That race was just a nightmare until the chequered flag came down, and everything broke loose."
Hamilton said that he was aware of the problems and was kept busy by the engineers as he was told to change settings in an attempt to protect the power unit.
"I could feel it," he said. "Obviously I've been driving this engine since the beginning, so I know pretty much everything there is to know about the engine and how it feels, pretty much every note of the engine I know like the back of my hand.
"It was OK at the beginning, but when I started to feel it now operating in its usual harmony – I mean I can't allow any worrying or negative thought to get in my mind, so I just stayed focussed on trying to do a little bit more lift and coasting, a little bit less full throttle load, even part throttle load, to make sure I go as easy as I can on the engine whilst doing the job."
He added: "My heart rate must have been above 190 or whatever. Those last 10 laps I was flat chat trying to hold on to the car that was already struggling with the tyres to keep the Red Bull – which was much quicker – behind, and plus not letting him get into the DRS for example."
Asked if the engine was supposed to be raced in Abu Dhabi and thus there might be some concerns about it, he said: "I've not thought that far! I'm not quite sure. Probably, yeah."
What made Ocon’s Verstappen move "unacceptable"
Gasly: Hartley should have passed me on merit