Well will it be ok to use fully synthetic oil for 1991 lancer which basically needs 10w-40 mineral oil?
If you say yes then I will use fully synthetic in next oil change. But should I use 5w-50 (Molygen, which is fully synthetic) or 10w-40 liquy moly MOS2 or Zic 5000 15w-40 or Delo Gold 15w-40 or ZIC xq 5w-40 or Synthoil 5w-40 or Xolvoline 5w-40 or shell Ultra?
And yes, there are many oil galleries still can be seen even from the top after draining the previous oil. I think this is impossible to drain 100% previous oil from the engine. But a couple of good oil changes will work. Anyway many thanks for the advice.
Sir what is PCV valve and where its located? I will ask mechanic to find it and make sure its working.