just curious if using a synthetic oil can you generally run a thinner weight oil or do you have to still stay in the same weight range? my car was designed to use 10w30 back in the 80's with dino juice but I am wanting to run 5w20 and wondering if I would have any problems .... help guys btw thanx m<x>ullet guys

Generally speaking, you run the same weight. The xxW # and -xx # are established at cold and hot temps, respectively, so you can typically go lower on the W #, but should stick with the same last #.

With a 20 weight (last #), the oil would be a little thinner at operating temp. Cars that are specifying that weight these days have somewhat tighter clearances, so using it in an engine with looser clearances intended for 30 weight could cause consumption issues. Wear probably wouldn't be a problem with a good synthetic, but it probably isn't worth the risk.

The lighter weights are intended to improve fleet economy.

just trying to figure out ways to get a little more gas mileage.
I know with some wider spread oils like 10w40 there tends to be more depsit issues with the polymers that allow the temp spread
would there be this problem with a 5w30 vs a 10w30?