DJR Team Penske bosses might have been worried when Fabian Coulthard sent his Falcon into a tryre wall in a wet and wild practice day ahead of the Sandown 500.

They need not have been.

Their pit team scrambled to fix the damage to the Ford No.12, and co-driver Tony D'Alberto took it to the top of the timing charts.

It was an up-and-down day for the Penske garage, and for much of the field in Melbourne.

Several teams flirted with disaster across three practice sessions, with only around 10 minutes of dry running at the start of the day.

Matt Campbell, Paul Dumbrell, Warren Luff and Steve Richards - co-drivers to series heavyweights - all ventured off the waterlogged track and into the grass.

But Coulthard's medium-speed crash was the most dramatic.

The championship aspirant lost control around turn seven, slid through a chicane and sent the nose of his Falcon into the wall at turn nine.

"It happened very fast," he said.

"It was a combination of weather and how slippery it is ... I came a cropper.

"We evaluate each corner when we get there and how we're going to get through it. That particular corner we didn't get through it.

"One minute the front was good, the rear was good, the next minute it was like I was on an ice rink. It's the nature of the business."

The wet weather meant times were well short of Jamie Whincup's 2014 practice lap record.

Co-drivers were the only ones to enjoy a dry run, when Nissan's Dean Fiore was quickest.

Among full-time drivers, Rick Kelly - in another Altima - topped the timing charts ahead of last year's winner Garth Tander and Chaz Mostert.

Coulthard's crash ended the session a few minutes early.

Kelly said the forecast Melbourne spring weather - with more rain on Saturday before clearing Sunday skies - presented drivers with a conundrum.

"It's always fun to be fast ... the last time I won a race was here in the wet," he said.

"But the scary thing is we might not run in the dry until Sunday.

When you're running 500ks in the dry with a setup you're not sure of ... it could be a really interesting race."

Qualifying races for the 500km classic take place on Saturday, before the race at 1:15pm on Sunday.