Mercedes' technical director James Allison described their opening day of the second pre-season test as "not the day we hoped for" after engine troubles derailed their programme.
The reigning champions revealed a major upgrade package on Tuesday morning which it will run at the season-opening race in Australia in a little over a fortnight, and whilst Lewis Hamilton was able to complete 83 laps during the morning, Valtteri Bottas, who took over in the afternoon, completed just seven.
The Finn completed an installation lap before moments later coming to a halt at Turn 3. The issue was blamed on a oil pressure issue which forced an engine change, eating up valuable test time and only allowing for a handful of laps to be completed in the closing minutes of the afternoon.
Allison is hoping for a better day tomorrow to allow the team to properly assess its upgrades.
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"It was not exactly the day we hoped for, running for the first time with the bodywork kit that we expect to use in Melbourne, with a large part of the day lost to an oil pressure issue at lunchtime.
"Nevertheless, either side of that problem we did do some useful things, finding that the car behaves a little differently with the new package.
"We’re looking forward very much to have a trouble-free day tomorrow to get a better feel for what it can do."
Both Hamilton and Bottas were at least pleased with the progress the team has made and both reported a feeling of improvement in the handling of the W10.
"We got through our run programme and the car was feeling relatively good. It was an improvement from last week which is a good step. The tyres are also working a better now that the track temperature is a bit higher. We have to continue to analyse everything and keep pushing," commented Hamilton.
Bottas added: "Unfortunately, after four days of flawless reliability last week, I spent most of the day waiting as we had an oil pressure issue on my first outlap and had to change the Power Unit. But I’m glad I still got to do a few laps, the team did a really good job to get the car out again; it was important to get a bit of a feel for the new aero package.
"My running was obviously very limited, but it seems like we’ve made improvements. We need to review everything in more detail tonight and I’m looking forward to continuing our programme tomorrow morning."
