Okay can we give round of applause to Jensen and his amazing acting skills like seriously I was so scared from this scene because that’s not the “Dean” we know anymore and yet look at Sammy he will go to the end of the world to save him even though I am sure he saw his eyes and felt it too but he won’t give up on his brother no matter what.
The Impala was filthy at the end of Reichenbach 10.02 but when Sam brought the blood back to the bunker at the beginning of Soul Survivor 10.03 it had been cleaned. That means Sam got his brother home, secured him in the dungeon, then headed to a car wash before getting what he needed to start the cure.
The Impala has been Sam’s home for most of his life, it gave him the strength to take control away from Lucifer, it comforted him the times Dean died and he was on his own. Dean may love the Impala most but it holds a special place in Sam’s heart too.