Mercedes have played down the loss of track time after an engine issue ended Lewis Hamilton's day early on Thursday.

Questions over the reliability of the Brixworth-made units are being raised with the works team and Williams now having used six engines between them, though Racing Point has continued to run smoothly.

What has been noticeable on track also is all Mercedes-powered cars have been giving off puffs of smoke at intermittent stages and some of the issues have been linked to the oil system, as was the case on Thursday.

Even so, while it was Mercedes' least productive day of testing for some time, Hamilton insisted his limited running still had value.

“Testing didn’t quite go to plan today but we’ll come back better and stronger tomorrow,” the world champion said.

“I only got 14 laps in today, but during those 14 laps, everything was feeling fine.

“It's obviously not ideal that we didn't get a full day of running in and we experienced this issue, but there are lots of learnings to take from today.

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“Rather than looking at the negatives, we've discovered some things we need to work on, and we'll keep pushing hard to resolve them and keep working away.

"I'm looking forward to being back in the car tomorrow morning and adding to the mileage we've already achieved.”

In total, Mercedes managed just 61 laps on the day as Valtteri Bottas' stint in the morning was impacted by external factors. 

Obviously, the running today in the morning was slightly limited with the wet weather, but we got a couple of runs in with the intermediate tyre, which is always useful," the Finn commented.

"We had a good feeling on that tyre in those conditions and gathered some good information.

"The session was also slightly disrupted by red flags, so we missed some of the test items we planned to do. However, we still completed a few good long runs and set-up work – so got some decent mileage in.

"I have one afternoon left in the car, which I’m really looking forward to. I feel pretty ready to race. We had a few issues here and there, but the team is working on resolving them and we’ll sort everything out for tomorrow."

And as the team looked ahead to the final day, technical director James Allison promised Mercedes would be upping the pace.

“We're looking forward to tomorrow, where we'll have a good amount of time with both drivers on the softer tyre compounds; working on single-lap set-up and performance," he revealed.