Engine oil weight and fuel economy

[Flatland2D]

I currently have Mobil 1 15w-50 in my engine. I did this in attempt to stop a smoking problem I had only at high rpms (started around 6k). Previously I had 5w-30 which was the recommended oil, but down here in Texas it gets really hot so I went up. I'm thinking about compromising with 10w-30. Anyone think I'll gain another mpg or two by using a thinner oil? I'll do at least one more tire pressure test to verify my results, but then it might be interesting to change my oil and see what happens.

[SVOboy]

I think that you can gain 1 mpg through switching your oil. I asked if I could run 5w 20 in my car a while back but I was told no by the honda people, so I am sticking with my 5w 30, but you're using really heavy oil now, I think you can go to 10w 30 without a problem if you can't use 5w 30.

[dfoxengr]

i use 5/30 in the motor, and 10/30 in the tranny for hondas...

you could use a lighter one, as long as weather permits it.

[SVOboy]

What kinda temps would I have to be in the use a 5w20?

[dfoxengr]

just warmer climate im pretty sure.

[chasgood]

5w20 is something Ford came up with. It is a synthetic blend.
I hear the best oil to save gas with is Mobil 1 synthetic 0w30.
As well as giving a bit better mileage you can go farther between changes. I use Mobil 1 5w30 and change it every 6000mi or 6months. If I had a non turbo car I would even go farther between changes.

[SVOboy]

I got 5k miles, what do you think about 0x30 in a car recommended for 5w30?

[dfoxengr]

Originally Posted by dfoxengr

as long as weather permits it.

[MetroMPG]

Originally Posted by SVOboy

I got 5k miles, what do you think about 0x30 in a car recommended for 5w30?

did you end up switching? or staying.

i'm also wondering about 0w30. how would you know if you were using too light weight? or would you just have to find out when your engine is worn out early?

[SVOboy]

Think you'd just have to find out and live with it, there might be a method to diagnose oil, but I do not know it. I ended up staying because I couldn't find 0w30 locally and the car was long overdue for a change. Got another change coming up in 2k miles and I'm waiting on results from h-t where a guy is dyno testing like 20 kinds of oil. (I'll try to pick my brand by this, but I'll want 0w30.)