Use exactly what your owner's manual lists as the recommended weight.
5W30 5W40 10W30 are all recommended for Nissan Stanza
You can use synthetic oil but I would not recommend 5w40. Use the exact weight oil as recommended by your owner's manual. Depending on the year it can be 10w30 or 5w30. 5w40 has not been used for many years. You can even mix synthetic with conventional oil.
5W40
Semi synthetic oil 10W30 or 10W40 (e.g. Mobil Super) Fully synthetic oil 0W40 or 5W40 (e.g. Mobil 1) Refilling capacity - approx 3 litres
Yes you can.
He 5w40 oil is a thicker oil at full operate temperatures than the 5W-30 oil.
If the recommended oil is SAE30 why would you use SAE 10W30? Some mowers recommend either of these weights but if your recommends 30W then using 10W30 will cause it to use oil.
Any name brand oil will do, but synthetic oils are better. Generally summer it is 10w30 and winter 5w30 for new cars and 10w40/10w30 for high mileage cars. However engine oil rated for diesel engines are best and you can get a synthetic diesel oil recommended by BMW from Bavarian Autosport, Lubro Molly, 5w40/10w40.
5w40 is a heavier weight oil at full operating temperatures, but are the same weight when cold.
Synthetic oil 5W40 with Renault standard RN0700/0710. Example: Elf Evolution SXR 5W40 Castrol Magnatec C3 5W40 Shell Helix Ultra 5W40 Just look for RN0700/0710 and you can't fail.
Personally I have had good luck using Rotella Synthetic 5w40 in my fiance's 4.0L Grand Cherokee. I don't do any towing, but I have yet to use a drop of oil in 5000 miles. This is on an engine with 100,000 miles and we purchased at ~83,000 miles. 5w40 may not be needed, but these engines (4.0L) do like a thicker oil. 10w30 is the recommended weight down to 0*F (for the 4.0L) and any 10w30 (regular or synthetic) will work well. Today's oils are extremely advanced and will protect well.
10w30 10w30