Best then to pour milk all inside his car in summer.
That's really nasty, it's near impossible to get that sour smell out. The only thing I have ever smelled that passed that on the stink-o-meter was a two week old corpse left in a car with the windows rolled up tight.
For the curious, an older gentleman was driving out to his deer camp, which was way out in the boondocks, accessible only via firelane when he suffered a massive heart attack and died. His buddies were already in camp and when he didn't arrive they assumed he changed his mind and was taking a pass due to his advancing years. His wife didn't expect any contact as the deer camp was way off the beaten path and she assumed he would be gone for at least two weeks. The result was nobody missed him until it was time to break camp and return home. Whereupon the former friends found his car where it had rolled off the firelane and stopped in the ditch with the engine running until the tank ran dry. The Sheriff called for a wrecker to extract the car and they towed it to the garage where I worked. People tried cleaning the interior of all soft trim and steam cleaning the bare metal but nothing could get rid of the odor. The car was finally scrapped out 'cuz nobody could stand to be near it.
Regards,
GtG