A man accused of killing his three sons by driving them into a dam has told the Victorian Supreme Court he cannot explain why he left them trapped in the water and went to find their mother.

Robert Farquharson has taken the witness stand for the second day.

The 41-year-old is being tried for the murder of his three boys.

They drowned when the car he was driving plunged into a dam near Winchelsea in the state's south-west on Father's Day in 2005.

Prosecutors are continuing their cross-examination of Farquharson and have asked him why when he escaped from the car, he left the scene and went to find the boys' mother.

"It was just something I had to do, I can't explain it," he said.

"She's the mother of my children and I wanted to tell her I had an accident."

Farquharson told the court he was a very loving father.

The trial continues.