Gas mileage and oil change -Is there relationship?

[TC535i]

One more question...

What affects the normal running viscosity more, the first or second number? What I mean is, I'm running a 15-40 now... will I get better gas mileage if I lower the first number, or the second? My guess is the second, but... somebody out there must know better than I.

[632 Regal]

first number designates the oils viscosity when cold and the second number is when its hot.

One more question...

What affects the normal running viscosity more, the first or second number? What I mean is, I'm running a 15-40 now... will I get better gas mileage if I lower the first number, or the second? My guess is the second, but... somebody out there must know better than I.

[TC535i]

first number designates the oils viscosity when cold and the second number is when its hot.

I know that, the 2nd number has to do with the max operating temperature before the oil breaks down. I figured that would affect gas mileage more than the cold pour point, but I wasn't sure...

[632 Regal]

I know that, the 2nd number has to do with the max operating temperature before the oil breaks down (WRONG).

I figured that would affect gas mileage more than the cold pour point, but I wasn't sure...

[ryan roopnarine]

the second no. is the viscosity of the oil at 100degrees C or (212F), it doesn't mean that the oil breaks down at that temperature, its just a useful benchmark for the "hot" operating climes of a combustion engine.

[ryan roopnarine]

tim, which brand of 15w40 are you using? what is the specified oil(s) supposed to be? there is data over at bobistheoil...... that could help you pick out the thinnest 40wt (and maybe one with the energy saving starburst) that might improve yer gas mileage some (as i assume this is a car that you are trying to economize as much as possible with).

[TC535i]

tim, which brand of 15w40 are you using? what is the specified oil(s) supposed to be? there is data over at bobistheoil...... that could help you pick out the thinnest 40wt (and maybe one with the energy saving starburst) that might improve yer gas mileage some (as i assume this is a car that you are trying to economize as much as possible with).

Definitely a car that I am trying to economize with... and that also means using whatever crap I have lying around.

Using diesel oil actually, the Chevron Delo 15-40.

[cary]

Using diesel oil actually, the Chevron Delo 15-40.

The Delo 400 15w-40 is probably the best mineral oil you can buy. It turns in great wear numbers, holds up longer than most mineral oils since it is an all fleet oil (technically it is a Heavy Duty Engine Oil or HDEO), has a robust additive package, and has a HTHS of 4.1. If you live in a climate where the temps don't go below 10f-15f and want to run mineral oil, this is the stuff to use.