I found some black liquid from the exhaust on my 2016 VW Jetta 1.4T after driving to Kroger located 0.5 miles out. 

Here is a little background, since my wife got a 2020 Corolla LE in June, I've been in love with that car and been driving it to work every day. I still have my VW because of my new work schedule starting late August and makes us need to have 2 cars. I have only been driving that VW once a week for less than 2 miles each time since we got the Corolla. The VW Jetta has 141k miles, haven't done the timing belt since VW recommends replacing it at 150k, no engine light. 

Question 1: Why there is black liquid in the exhaust pipe? 

Question 2: I am really hoping to trade in this car in mid-Sept for a RAV4, (Can't do it earlier due to some personal issue) what else in terms of maintenance should I do to last the car until mid-September? I will be driving it a total of 70 miles highway a day for 5 weeks from late Aug. 

Thanks