Originally Posted By: max45
i was thinking because is got high miles on motor to switch to 10w-40 weight oil, i'am going to desert area one of this days, where temp will be 95f +.i don't know it's just my thought, maybe i'am wrong
You are not "wrong," i understand the logic, had car or newly acquired so you think going one grade up on oil preserves its innards better. FWIW, your car will run fine on 10W-40 or 30.
What you are worried about is the oil "thinning." Does the car overheat? It takes some getting used to, but if the 30 had no issues, then it will protect the SAME in high heat, as long as it doesnt degrade or get too thin in the engine at high temp. There is a measure called "KV100" as to how thick it is at operating temp, and your oil may get a bit hotter than 212 degrees fahreneit. There is a more reliable measure called HT/HS, and that is how "thick" the oil will be while in your engine.
Long story short,if the 10W-40 feels good keep using it. There will be pages as to why its not ideal, but if it works it is fine and it may make your engine feel "different" some like the wait feels thicker, some thinner. I could go either way, and your choice is ok. (You could have also left it the same but i understand your thought train, max45.)
If you start going the thinner is better route, you will never stop trying to find the very thinnest oil you can get in there
For your car, a 30 was originally spec'd, and a 20 was possibly back-spec'd (meaning the manufacturer said it was Ok after it was produced.) Your oil choice is, in the end, up to you.