Nissan Repair: conventional oil or synth, nissan almera, dune buggy

Question
i have a Nissan almera n-16 model its a 1.6 gas engine since i had the car i have been using castrol 20-50 conventional oil i want to switch to synthetic oil i would stay with the same brand i jus wanted to know if this is possible or is it bad for the car and if not what body should i use as its replacement i live in the caribbean and i average being in traffic at least 2-3 hrs a day presently the car is doing  70,000 km thanks in advance

Answer
Gary,

Mobil 1 5W30 is what I would be using or your favourite oil.  If your bearings are loose the 20W50 is fine.  But, if you note high oil pressure you could switch to the lower viscosity and save money on fuel.  The thicker oil is harder for the oil pump to push through the galleries.  So, if the engine is tight you can get away with the 5W30.  Here is the US Nissan recommends 5W30.  On the subject of synthetic oil Nissan does not recommend using it ever.  Me?  I use Mobile 1 5W30 synthetic in every car I own an that includes the Dune Buggy, the 350Z, Corvette, Maxima, Stanza, Camry...  Even the generator uses synthetic.  The only thing you have to worry about is using it in a new or newly rebuilt engine.  Since it is so slick new rings will not seat.  I put 1500 miles on an engine before switching to synthetic.  Others recommend 5000 miles.  But, you are way beyond that so it would be fine.  A word of warning though is that if there is a seal in the engine that is weaping it will be leaking with synthetic.  So, be sure to keep an eye on the engine for new leaks with synthetic...