so i bought this a4 from a non audi dealership, and it had engine oil leak and the stock coolant reservoir had cracks in it and leaking a little too so i took it back to the dealer's shop and they fixed it, turned out it was the drain plug or something and they gave the car a new one, and for the coolant they said it was probably due to heat and cold + chemicals that made the stock coolant res. crack, so they replaced it... that was like 3 days ago.

Problem 1:
I never noticed this but when i turn on the car after like a 12 hour rest for the car, the temperature gauge goes from low to medium the moment i turn on the ignition... thats pretty abnormal espeically since it never did that before when i first bought it.

Problem 2:
After the dealership's shop replaced the reservoir it seemed fine for the last 2 days but on the 3rd day, (today) i drove like 15miles and the temp. gauge went from medium to borderline touching the marker between the medium marker and the Hot marker. Then after working for 8 hours and i leave to drive onto the freeway, within like minutes, it went from medium temperature to between medium and hot again. Went i finally i got home, i touched the hood, it was cold, so i thought itwas just the winter nights and opened the hood, the engine was far from warm, it felt cool too. Can anyone diagnose the cause of this? i'm going to complain to the dealership... again.... tommorow. Car has 71k miles on it if that helps at all. Thanks

problem #2 only occured after the new resevoir was installed and for problem #1 i don't remember when it happened... could've been before or after the reservoir replacement but when i first bought it, i was able to witness the car slowly go from cold to medium temp during my drive.