Jarno Trulli admitted he was hoping for a better day as testing kicked off at the Jerez circuit on Thursday.
The Lotus driver managed only 54 laps as he was hindered by problems that forced the team to stay in the garage for quite some time during the eight-hour session.
Trulli finished as 10th quickest, 3.7 seconds off the pace set by Felipe Massa.
The Italian conceded it was not the day he was hoping for, but insisted the new Lotus has shown potential.
"It was less than we expected but nevertheless we put in some good laps," said Trulli, "unfortunately we didn't manage to do any set-up work because we had some troubles every time. So it was not the day we wanted, but the car feels pretty good and has some good potential in it.
"Now we need to put in some more laps for more consistency on the track because if we keep breaking down the runs we will never manage to get a real idea when we change the set-up to have a comparison. So it's important for the next few days that we do this job.
"It was nothing serious, we had a leak from the rear end. I'm not really aware of what it was exactly. And then one of the bolts dropped into the gearbox so we had to take the gearbox apart. Just silly things, but on a brand new car with such a complicated rear end... it can happen. We are working on these things."
He believes the car will be more competitive once the team fits all the new pieces to it.
"We are still waiting for some bits and pieces to come on the car so we don't yet have everything in place. There is more potential in the car. It was extremely promising this morning when we were able to get some laps and some runs in. That was looking pretty good. The afternoon was spoiled by these problems.
"The bad thing is that we haven't done much today, that's the only bad thing. I'm not concerned about the set-up because we will get there. We first need to get everything in place and get the reliability fixed, we need some mileage to solve the problems and get used to the car and tyres together and I think there is quite a lot of work to do on that matter."
The Italian also admitted he was struggling with Pirelli's tyres, but reckons some set-up work could solve that once the team has time to carry it out.
"I'm not particularly happy about the tyre's behaviour, to be honest," said Trulli. "At the moment the car is dominated by the tyre behaviour, so we need to find out how to use the tyres.
"The degradation is high, the rear end lateral support is very poor, so one of the keys is probably there but as we haven't done many set-up changes, I really now struggle to tell you exactly what we should do. This is one of the areas we need to concentrate on.
"I'm struggling a little bit with the handling and with the rear end. They drop off very quickly and so it's also difficult for us to make competitive runs to set up comparisons because from one run to another we have another degradation.
"The rest seems okay. The car under braking is very much balanced and stable. We still have to investigate more on the ride height and front wing angle. We have been using today the rear moveable wing which was working really well. So we are getting there, but obviously missing half the day was a pity."