Marcus Ericsson returns to the track in the Sauber. A strong start to the year for a team that had some serious financial questions hanging over it last season. Let's hope for a return to form the small Swiss squad.
And we have a Toro Rosso for the first time today with Carlos Sainz behind the wheel.
@robert: No sign of it yet, but McLaren have been Tweeting from the garage...
But it's going to be a tricky week for McLaren. Getting an all-new power unit up and running is not easy as we found out last year with Renault.
@Prajesh: No full lap times completed yet. Ericsson leads the lap count with three laps. Rosberg, Vettel, Ricciardo and Sainz all have a single lap under their belts.
@anthony: Not massively, no. And sadly they are no louder than they were last year. However, I'll head down to the track later this week to see if I can hear any subtle changes in the sounds of each individual power unit.
When the Honda ran in Abu Dhabi (albeit briefly) it had a very nice and raspy exhaust note. So I'm looking forward to that heading about again this week.
Ricciardo is back on track, which is good news for Red Bull fans. This time last year they were struggling just to get the car fired up and still they finished on the podium (albeit illegally) at the first race. Once again, they will be among the teams Mercedes fears most this year.
@imrohit_: There's every chance it might be. The engine has been in development for over two years and the rumour is that it's got a similar split turbo charger like the Mercedes'. There are also some positive noises about its power output. The big questions will be over reliability and driveability, which all the manufacturers struggled with last year.
@XanBex: That's the plan. And day 4 too!
Ricciardo set a time on that last run with a 1:29.141. That's our first lap time of the 2015 season.
@SpittingCobra: Ricciardo went out on mediums to start with. But I'm not sure if that was just to match the black and white of the colour scheme ;) In all seriousness, the times from this morning (and most of this test) won't tell us that much.
@WAY: Pretty tricky. The most notable thing so far is the size of the sidepod openings. Clearly Renault has worked hard on reducing the cooling needs of its power unit and Red Bull has used that to tightly package the bodywork with the aim to reduce drag and boost downforce.
@PhilPhelan: All the manufacturers have made big strides with cooling. Reducing the radiator size is one of the big challenges of this new engine formula.
@8RE_HA8: Rosberg has just gone back out . So if there was smoke it was nothing major. We certainly didn't see the engine blow or anything like that.
And there's the first time from Rosberg. A 1:26.993 to set the fastest time so far.
Vettel has also set a time now with a 1:35.218.
Impressive stuff from Mercedes. The car is now on its seventh lap and is improving with each lap. Now down to a 1:23.653.
Red flag. It looks like Ericsson has stopped on track in the Sauber.
I think we just heard a Honda fire up for the first time directly underneath our media centre.
@Siddhesh: Understandably the teams want their cars back, and they usually have to come back to the pits on a flatbed truck. For safety reasons all the cars come back to the pits first
@Carlito: Whatever the FIA try to stop the teams try to find a way round. Last year's cars were slower than 2013 at most tracks, this year's cars will be quicker no doubt.