Why a new Honda F1 engine problem was brutally exposed

Honda got caught out by its Formula 1 engine’s lack of robustness in a new way in Mexico, which has already prompted countermeasures for this weekend’s race in Brazil.

A disastrous double-DNF occurred almost simultaneously for Aston Martin’s two Honda-powered cars last weekend, when Fernando Alonso stopped on track and Lance Stroll came back to the pits and retired in the garage after just five laps had been completed.

Honda had been wary of the challenge posed by Mexico’s high altitude but felt the mitigation it had worked on to combat the thinner air would be sufficient. Instead, Honda’s trackside boss Shintaro Orihara said the main “learning point is our engine, in special circumstances, there’s some lack of robustness”.

Aston Martin’s practice mileage was normal - an issue for FP1 stand-in Jak Crawford was of a different nature - but it emerged in qualifying that Honda faced serious issues and both parties knew well in advance of Sunday’s race that the cars were unlikely to finish.

The cooling demands of Mexico seemingly exposed an unexpected fragility within Honda’s engine that was triggered by special running phases - like a tyre preparation lap in qualifying and the formation lap to the grid.

This caused the engine to “behave a little bit abnormal”, according to Orihara, with stress put on its energy recovery system’s cooling circuit and a subsequent MGU-K failure.

The problem was not directly related to typical car cooling challenges like running in traffic, or how the car’s bodywork was impacting its heat-rejection capacity.

It was also not a question of faulty specific parts as Alonso had an MGU-K change mid-weekend and Stroll used a completely different engine, which as chief trackside officer Mike Krack noted pointed to “more of a general problem”.

Orihara also said it was not a problem detectable in simulation, but would be on the dyno, which means it relates to a physical interaction and will be incorporated into Honda’s future dyno work.

The two cars effectively suffered different stages of the same failure - one with rising water pressure, one with pressure dropping too low. This just means one went further down the same path - as the drop comes when the water pressure rises, then a leak starts.

It suggests an engine usage problem causing a downstream effect on ERS cooling, as it relates to the operation of the V6.

Presumably the stress on the ERS cooling circuit relates to coolant pressure rising in a sealed circuit, although Orihara did not elaborate on specifics for how an engine misbehaving would cause that or whether Mexico’s thinner air had a specific impact like lowering the coolant’s boiling margin.

The problem spiralled early and could not be contained. There were some measures lined up to mitigate the issue like pitting the cars for free air - which is why both cars initially came into the pits at the end of lap three - and being more cautious with gear usage and reducing power.

“You have a list of options that you can pull,” said Krack. “But we quickly realised that they were insufficient. And there’s nothing you can do then.”

The lessons from this will be adopted into Honda’s development work for 2027 but Orihara said Honda has also brought some fixes for Interlagos this weekend, which is nowhere near as stressed as Mexico but is still a higher-altitude race.

The countermeasures relate to software and calibration, and on the hardware side. Orihara did not elaborate what these were but presumably they relate to controlling how the engine behaves in those special running phases, and the circuit’s ability to contain the pressure given the leak that occurred in Mexico.

There was another aspect to the Mexico challenge that Honda was not as well-prepared for as it thought. Despite readying something altitude-specific, it suffered more severe turbo lag at the start, when the engine’s exhaust energy was low and boost pressure dropped, with Orihara admitting “our software doesn’t have enough robustness for that condition” either.

The double DNF triggered an unusual sight in Aston Martin’s post-race report, in which team boss and technical chief Adrian Newey was quoted with a single line that read: “It has been a disappointing day, especially as Fernando showed very good pace all weekend.”

Asked about that, Krack said: “I think nobody was happy. We have had a lot of DNFs, another double DNF [in Mexico], and nobody can be happy. And I think it’s the same for him.”