Heikki Kovalainen believes there is more to come from Lotus after a "challenging" Friday in Brazil.
Filling in for the injured Kimi Raikkonen in the season finale, Kovalainen showed some solid pace in the rain in the afternoon's session.
The Finnish driver brought his car home in fourth place with a 1:28.129, which put him 0.823s behind pace-setter Nico Rosberg.
It was meant he finished 0.762s quicker than Romain Grosjean.
"Obviously, it was challenging conditions but it was good for me to get the experience in the wet weather," said Kovalainen.
"There were no big surprises and the car was behaving quite well. It was a little bit trickier than driving in the dry, but we expected this.
"That said, I think the team have made good progress in this area as it wasn't too difficult to drive.
"There are still a couple of areas where we can improve on, and whether we have valid information for tomorrow's weather we don't know yet."