the previous owner of my car used 5W30 oil, but looking over some receipts where he had the fuel injectors replaced by MazCare (a reputable shop in Atlanta) it says they put in 20W50. Also, when the oil was changed, they added an oil cleaner to make it less sludgy, but reading up on 20W50 it seems to me that you should be using a thicker oil in the rotary for heat purposes. i've already put in 5W30 for the current oil change, so should I be okay? also, synthetic vs non synthetic...which do you guys use?

 

https://www.rx7club.com/forum/showthread.php?t=68640

Here's a good past discussion that gets into more detail:
https://www.rx7club.com/forum/showthread.php?t=721879

If you want more discussion, run a search.