tomorrow i will change my engine oil but i want to know if i should use some of that engine flush liquid that i bought which states to pour into the engine and idle engine for 3 mins and do oil change and filter change. i did flush at some lube store from last oil change (but they didnt idle the engine, just poured it in and out). i m thinking of doing the flush because i went over 3000 miles by around 50 miles more, and using nonsynthetic oil. should i do the flush or return it to store?

 

I would return it, it is really pretty much unnecessary, and btw - 3050 miles is still less than the mileage interval Nissan states in the manual, so you should be fine.

If you are really worried about cleaning out your engine, I would buy a bottle of Auto-Rx and follow their cleaning instructions.