Jenson Button had to switch back to the Honda Formula 1 engine he used for the Monaco Grand Prix due to an oil leak on his McLaren in Canada practice.
Button left the garage amid plumes of smoke in first practice and hastily returned to pits at the request of Honda.
In the gap between sessions, Honda reverted to the internal combustion engine Button used in Monaco – which has done four races – but fitted a fourth updated turbo, MGU-H and MGU-K as a precaution.
Following investigations, it will make a decision late on Friday or early Saturday morning as to which unit Button will run from third practice onwards.
“We put the old engine back in and we had no issues with how it was running,” said Button. “The guys did an amazing job. We just have to decide tonight what engine we use tomorrow – whether it’s the one we put in on Friday or the engine we’ve used for the last few races – but I think either way it will be fine.”
Button, who finished seventh in second practice, was pleased with the pace McLaren has demonstrated so far this weekend and was hopeful the team could have a strong weekend despite expectations that it would struggle on the long straights in Montreal.
“I said before that people were going to be a little bit surprised at our performance here and we weren’t going to be any worse than Monaco,” said Button. “It’s very close in the middle of the pack. If I went half a tenth quicker I would’ve been fourth, and two tenths slower I would have been 11th or 12th.”
When asked if Q3 was possible, Button said. “I think so.
“You’ve got to aim reasonably high and try and get the best qualifying we’ve had all year, and doing it here would be great.”
Speaking about the update to the turbo, which involved Honda spending two development tokens, Button said: “It’s not for outright pace, it’s more for efficiency and it only benefits us in the race.
“We also have new fuel here from Esso which is about a tenth of a second, which obviously helps.”