Gas mileage and oil change -Is there relationship?

[Russell]

Thought someone on this board stated that they changed their oil when their gas mileage started going up. It seemed to indicate that it needed changing?? Tell me more about this? I think I have noticed something similar. I use Mobil 1 0w40.

Just interested. TIA

[Derek A.]

lighter oil less friction - less parasitic horsepower loss from the oil pump not doing as much work. Only downside is that you have less keeping the internal engine pieces from hitting each other

[Russell]

I mean that as you accumulate mileage, after an oil change-say 5,000 miles later, the gas mileage starts to go up.

Someone seemed to think that increased gas mileage indicated you needed to change your oil. It does not make sense to me. It would seem there is less friction when oil is new and as it "wears" friction would increase and mileage would go down,

just puzzled.



lighter oil less friction - less parasitic horsepower loss from the oil pump not doing as much work. Only downside is that you have less keeping the internal engine pieces from hitting each other

[632 Regal]

it builds up cabon in the oil from the burned gasoline. Your oil filter takes out particles much larger and cant ever take the carbon molecules out. The carbon isnt a "lubricant" agent and adds to friction after a point (gets black), not necessarily a wear agent but kinda gums up the clean oil and adds stuff that isnt preferable. In that time when the oil builds this stuff it also collects other things like unburnt fuels from blowby, any additives in the fuel that arent burnt and so on. If you could filter the carbon out and the unburned addatives synthetic could virtually last forever. In the race car I would only use 3000 mile used synthetic because there is a point where the friction actually gets lower with a certain amount of carbon and causes less parastetic loss. Anyways, I'm old school and certain things stick to my old brain. Change your oil about every 7500 miles and be done.

[Paul in NZ]

less friction when oil is new and as it "wears" friction would increase and mileage would go down
thats what they prolly meant,consupmtion goes up...I would think it would be hardly noticeable,and well within the variation you would get with traffic jams,italian tune ups,needing to pump up your tires....etc

[TC535i]

I put 15-40 in my Kia this change instead of the 10-30 I normally use, and I've noticed my gas mileage go down 1-2 mpg

[632 Regal]

I put 15-40 in my Kia this change instead of the 10-30 I normally use, and I've noticed my gas mileage go down 1-2 mpg

[winfred]

the theary was that the viscosity had busted and the oil was getting lighter, i think that's what ryan was talking about

[ryan roopnarine]

let me clarify....

my experience with mobil1 oils, as they are generally made on the borderline of thinness WRT the viscosity they are labeled as (5w30 almost a 20)....is that in my car, the mobil1s generally go out of grade by increasing MPG. with, for example, cheapo walmart 10w40, the car generally goes out of viscosity range by getting fatter, IE i know its time to change when i start losing gas mileage because that oil is constructed near the top edge of its viscosity rating (w40 almost being a 50wt). YMMV depending on the condition of your motor, but i was doing a lot of highway miles at the time (2k per month) and could notice when the change occured because of the amount of time i was behind the wheel.

[TC535i]

too thick, use 0w40 Mobil one and see an improvement.

Uhh... yeaaaaah...

I'm not putting Mobil One in my Kia, that would go completely against everything that car is intended for! I refuse to spend any more than $1/qt, and $3 for the filter. Doing an oil change for <$10 is AWESOME. :D

[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. :p

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.