Oil viscosity vs MPG

nickmckinney · Aug 23, 2005

quote:

Originally posted by Doc Holiday:
car makers recommend thiner oils to help them with CAFE (corporate average fuel economy). If they can get .5 to 1 more mpg out of a car then that helps them alot. Don't you find it strange that Ford is saying to use 5w20 even in some car that the year before it said 5w30, and no engine mods were done with the model change. You don't see the guys a indy useing 5w20

Well 2 problems, Ford motors specing 5W20 are doing pretty good on this site using MC 5W20 oil once the numbers are run. Its kinda hard to spec 5W20 when there wasn't any readily on the shelf 10 years ago............

And Indy is another world compared to your car. Indy, Nascar, and most high end drag race engines are high vacuum dry sump designs. That is there is an oil tank and heater combo somewhere not attached to the engine like your daily driver oil pan. Its alot easier to use a 50W once you have an electric heater take it up to 160F before you fire the engine. There are also many race instances where a 20W is considered THICK, Nascar qualifing comes to mind.

Like they say, YMMV, but mine went up about 0.5MPG going from 30W to 20W on a Ford 4.6, and if there is no extra wear or consumption, then why run anything different?

tenderloin · Aug 23, 2005

"Don't you find it strange that Ford is saying to use 5w20 even in some car that the year before it said 5w30, and no engine mods were done with the model change"

As far as we know Ford gets no Brownie or CAFE points for back recommending 5W-20...so your point is what?

Technology changes..some people won't change with it. It is that simple.

"Gol darn it" straight 40W is the only oil I will ever use...none of that new fangeled multi numbered stuff for me".

"5w30? LOL, NO WAY! 10W-40 by golly is the only oil I will ever use"

5W-20 is not for all applications, but where it is recommended it seems in real world testing to be doing a great job.

Don't like it? Don't use it but don't trash it either.

`

Mickey_M · Aug 23, 2005

quote:

Doc Holiday:

.... Don't you find it strange that Ford is saying to use 5w20 even in some car that the year before it said 5w30, and no engine mods were done with the model change. ....

Not in the least.

The flak they're taking over it, as is Honda etc, and the fact that Mobil 1 0W-20 was dropped for 5W-20 tells you why they delayed doing it: the bias of the buying public.

SAE 20 motor oils have been all most cars and trucks needed for years, at least with synthetics.

Why do you think 10W-30 motor oil sells long after most manufacturers started recommending 5w30?

.

Shannow · Aug 23, 2005

When I ran 25W-70 in my camira, it belted fuel economy by quite a few MPG over 40 and 50 weights.

427Z06 · Aug 23, 2005

quote:

Originally posted by Shannow:
When I ran 25W-70 in my camira...

No girly-man oil for this dude.

Shannow · Aug 23, 2005

It was back in the "Thick Oil will kill your engine" debate a few years ago.

So I ran 25W-70 (300 plus cst @40) through winter, and straight 30 through summer.

No UOAs, but a big mileage hit.

http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=1;t=003049#000000

Thanks to this board, nothing heavier than a 40 weight has been in any of my vehicles for 2 years.

mdocod · Aug 23, 2005

You could probably run an engine on vegitable oil for awhile.

Ugly3 · Aug 23, 2005

quote:

Originally posted by Shannow:
It was back in the "Thick Oil will kill your engine" debate a few years ago.

So I ran 25W-70 (300 plus cst @40) through winter, and straight 30 through summer.

No UOAs, but a big mileage hit.

http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=1;t=003049#000000

Thanks to this board, nothing heavier than a 40 weight has been in any of my vehicles for 2 years.

You and Gary Allen better never get together!

TooSlick · Aug 23, 2005

Generally going down one SAE grade will improve fuel efficiency by 1.0%-1.5%, depending on the rpm range the engine runs in. Pumping losses associated with using a thicker oil increase as a function of engine rpms (think of the textbook case of viscous fluid flow through a pipe).

The very high rpm, four cylinder engines like Honda/Acura/Toyota/Mazda RX8, suffer significant loss of power and fuel efficiency using thicker lubricants. A low rpm, high load application will suffer little or no loss of performance and may even do better with a slightly thicker lube, particularly if the engine is excessively worn and the ring/cylinder clearances are comparatively large.

Tooslick

oilyriser · Aug 23, 2005

I tested my Subaru on two trips at 100 km/h, using 10w30 and 15w40. The 10w30 beat the 15w40 by only 2.5%. At higher speeds, the difference would be less, since oil drag would be a smaller fraction of total power.

eljefino · Aug 23, 2005

quote:

Originally posted by TooSlick:
Generally going down one SAE grade will improve fuel efficiency by 1.0%-1.5%, depending on the rpm range the engine runs in. Pumping losses associated with using a thicker oil increase as a function of engine rpms (think of the textbook case of viscous fluid flow through a pipe).

The very high rpm, four cylinder engines like Honda/Acura/Toyota/Mazda RX8, suffer significant loss of power and fuel efficiency using thicker lubricants. A low rpm, high load application will suffer little or no loss of performance and may even do better with a slightly thicker lube, particularly if the engine is excessively worn and the ring/cylinder clearances are comparatively large.

Tooslick

This is exactly why I run 15w40 in my SOHC saturns that I typically lug at around 1700 RPMs. One should consider their typical RPM range when picking an oil or at least comparing against others. If I had an automatic trans in the same car I might run 10w30 since it would downshift against my control and the torque convertor wouldn't lug the motor/ load the bearings/bores as badly.

MNgopher · Aug 24, 2005

I ran 5w30 nearly continiously until I found this board in my '99 F150 with the 4.6l V8. I decided to experiment over 1 year intervals running 5w30, 5w20, and 5w40 oils. I'll grant that oil specifications changed along the way (SJ to SL and now SM), and the brands weren't identical, but I still found the results interesting.

I keep meticulous fuel records, and I found statistically no difference between 5w20 and 5w30 oils over a 1 year interval on each. I ran 5w40 for a year, and my fuel mileage decreased by over 5%! Wear numbers were ever so slightly better on 5w40, but not nearly enough to justify a 5% fuel mileage penalty.

I've since returned to 5w30, and my fuel milage has been restored.

On the other hand, my old Jeep Cherokee gets the same fuel mileage year around running 5w40 as 10w30/5w30.

All depends on the motor and application.

427Z06 · Aug 27, 2005

quote:

Originally posted by eljefino:
This is exactly why I run 15w40 in my SOHC saturns that I typically lug at around 1700 RPMs.

I believe if you look at the Sommerfeld number for this design, anything above 600 RPMs is considered "high-speed".

Doc Holiday · Sep 12, 2005

ok...you guys have almost converted me to thinner oils.....but why would the OM and the oil cap on my 2002 chevy impala with a 3.8 v-6 say to run 10w30 and yet my 1995 chevy 4x4 truck with a 5.7 v-8 say to run a 5w30. This doesn't make alot of sense to me....

Oil viscosity vs MPG

Similar threads