van Slooten will be the fifth different driver to climb into the cockpit of a BD01 this season.
Kip Maxwell is still out on paternity leave and sports psychology sessions while Felix Beyer is in a Dutch hospital undergoing medical check after he fell ill during the Austrian Grand Prix weekend.
It was confirmed earlier this season that Team 23 would use Downton engines as of next season and that the teams would also both benefit from a technical tie-in.
Team 23 have now confirmed they will allow their test driver - Jacinto van Slooten - to race for Downton for as long as necessary during the remainder of the season so they can see how he'll perform in a race situation.
It is believed that no fee will be incurred to either team as both teams are set to gain from the loan.