Originally Posted by SKULL_FACE

I use to have a Nissan Xterra, everytime I changed the oil, the engine was much responsive. a month later not even 500 miles after the oil and filter change, the performance went down. I have not noticed this on our Wranglers' but it does exists on some vehicles. Later I learned from a Nissan Mechanic that the engine I had in the Xterra , was a high Compression engine that broke down the oil very quickly. The new oil would be jet black within a month. Did not keep it long enough to say if it had issues later on. Should have switched to a quality synthetic oil.

I myself am switching from 5w-20 to 5w-30 weight. Currently using Mobil 1 Advanced Synthetic oil and a Napa Gold Oil Filter made by WIX, since switching to a Synthetic oil 8 months ago, I have seen a major difference on how my engine sounds better , longer time before dry starts,etc.

I do have one question though,, What is the true meaning of the first number ex: 5w labeled on motor oil. I thought it was the weight of the oil's viscosity referred to when the engine is first started, then the last 2 digits meant "IE: 20 or 30" took over when the oil is warmed up form idiling and now is reaching the higher end of the oil's operating characteristics under varying conditions,, temperature, towing, long idle, large hills, etc. Is this correct in a non technical way? lol.

Thanks,
*** SKULL_FACE ***

Originally Posted by zstairlessone

the real beauty is with the higher operating temperatures on the engines today the 5W-30 is BETTER than the 30W at temperatures above 100C and still allows easier starting when cold.

Originally Posted by EzK

Are you assuming that the oil thins in a linear way and continues to do so after 100° or is that fact?

Originally Posted by Bushmaster

So it will start cold with the oil at the thickest of the thin oil and at temp it will be the thinnest of the thick oil yea?