Sir use 10w 30 grade mineral oil for your car which is available on caltex... 20w 50 is wrong, it may have bogged down your cars performance...
Synthetic is good but only go for it if you can afford to stick regularly to it and if you can find authentic products ... try liqui moly...
Use a good oil filter, and change oil of the car when engine is hot...
Cheers...
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