I recently bought a GTX 1660 Super (single fan) from the used market. In the initiation state of the benchmarks the temperature immediately jumped to high 70's which worried me quite a bit. However, I took the graphics card apart, cleaned out the dust from the heat sink and fan and proceeded to replace the thermal paste. After that, the temperatures of the card did not immediately jump to the high 70's which was a relief. Although, when I was gaming (CSGO) the temperatures remained averaged at 80 degrees with the maximum temperature being 83 degrees. 
 
I am not exactly sure what temperatures the expected temperatures are for this card but I assume they should be in the high 60's or low 70's. Wanted to get an opinion on whether or not I should RMA this card. It still has 665 days of warranty left.

It depends on your case airflow setup. 80+ degrees is to be expected, especially for a single fan card. Are you getting good airflow in your case? Those temps are on the higher end but not unsafe.