Sandy Grundy and her daughter Jessie were driving from Adelaide to Mundoo Island, where an hour from their destination the snake peered out from under the bonnet.

Ms Grundy and her daughter continued the drive fearing their new passenger would join them in the car. At the end of their trip the pair left vehicle in the middle of a paddock hoping the snake would find its way out.

Ms Grundy described her fear in a Facebook post. "It scared the living daylights out of me! Petrified would sum up my nervous state for the hour I had to drive," she wrote.

She told The Advertiser, "My initial fright at that split second was I wasn't sure whether he [the snake] was inside the car or outside the car — that's what the fright was."

"The worst part was for the next hour that I had to drive, he kept disappearing. I got used to the fact that there was a snake in the car and preferred to see him than when he disappeared."

Ms Grundy and her husband Colin re-checked her car on Wednesday to find the red-bellied black snake still curled up next to the engine.

The video posted to the Mundoo Island Station Facebook page has had over 70,000 views in 20 hours.