East African youngster Kimathi made his junior debut at Rally Sweden in February where he was co-driven by fellow Kenyan Mwangi Kioni. The pair also contested the Croatia Rally, but retired on the final day.
Kioni will step aside for round three of the championship this week as Loudon takes the reins, but he will remain present and heavily involved behind the scenes at the Matosinhos-based fixture.
Kimathi told WRC.com his reasoning behind the temporary move.
“I just really thought about things and I thought we both needed to learn from somebody who can help us to understand more about what European rallies are all about,” he explained.
“It’s just a one-time move as a kind of benchmarking tool to help both of us. I picked Stuart because he’s competed in Kenya with Onkar Rai and he also understands these types of rallies.
“It’s just to help me get to this level that the other Junior WRC drivers are at, to get to that benchmark level,” he added.
Loudon has started almost 150 rallies, including over 20 FIA World Rally Championship events.
He previously joined M-Sport Ford driver Gus Greensmith at Rally Italia Sardegna last season and also contested the 2012 junior series with his Scottish compatriot John MacCrone.
“I think my role here is really just to try and push the experience of Mcrae and Mwangi,” Loudon said.
“It’s obviously been a big transition for them, coming from Kenyan rallies to the WRC, and in fairness to them, they managed to get through Sweden and Croatia. That’s not an easy task.
“Hopefully I can pass on the best of my knowledge this weekend and get Mcrae to the finish. That’s going to be the main objective,” he added.