Oil and Gas Mileage?

[Giles]

How much impact does oil weight have on gas mileage? If I get 19mpg highway, and I'm running Mobil 1 5w30, what fuel reduction would I expect if I switch to Mobil 1 0w40?

I probably won't switch, just wanted to see what others experiences are with oil weight and gas mileage. I know for instance that Ford expects between .1 and 1% increase by switching from their 5w30, to 5w20. I suspect there is less of a difference in viscosity between 5w30 and 5w20 than there is between 5w30 and 0w40 so I should expect more reduction than that range I would think. Would you guess in the 1-2% range?

 

[ryansride2017]

Why would you expect a fuel reduction going from Mobil 1 5W30 to 0W40?

I believe the only way you will decrease your mileage from 5W30 is to wait until Mobil comes out with their synthetic 0W20 (and you probably won't gain much at that).

[ January 09, 2003, 09:40 PM: Message edited by: ryansride2017 ]

 

[Giles]

Maybe I wasn't clear, I expect gas mileage to get worse going to 0w40, but by how much?

 

[Bub]

I went from running 10W-30 mobil 1 to 15w50 mobil 1 and I am getting roughly the same milage (within 1 to 2 mpg). And in a LS1 Z28 thats an easy tradeoff to help reduce piston slap. I am also considering running 0W-40in the truck instead of the 10w30 that I currently use. Hope that helped
Bub

 

[vvk]

I picked up about 10-15% improvement in fuel economy after switching from xW-30 to xW-40 in my SAAB. This result is consistent with what some other people who own SAABs have reported.

 

[Giles]

vvk, I find it surprising that fuel economy actually improves for you! Were you using a 10w30 or 5w30 synthetic before switching to 0w40?

 

[ZR2RANDO]

After about 50k I usually use thicker oil on vehicles than while under warranty. I have a 99 s10 ZR2, used 10w30 through the warranty period. On this particular vehicle, When I first "thickened up", (swapped a qt of 20w50 for a qt of 10w30), The fuel mileage increased, typical is 19-20mpg and after switching changed to 20-22. I check fuel mileage on all my vehicles, every tank. On my oldest vehicle at the moment (1989 Nissan 4X4 at 189k miles), I used 10w40 while it was young, and started adding some STP after it got "older", mileage did not change after starting to use STP.
Personally I do not care for thin oils on vehicles, 10w30 is marginal as far as I'm concerned (I do not live in extremely cold climates, so my opinion is regionally influenced)
Thin oils are probably car savers for folks up in frigid north areas, but here in NC or south of here, I go with "thicker" myself.
I have never used synthetic oil, but if I lived up in the frigid north I probably would think about it...just due to extreme cold flow/stability properties.
good mornin everybody
Rando

 

[msparks]

quote:

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Originally posted by Giles:
Maybe I wasn't clear, I expect gas mileage to get worse going to 0w40, but by how much?

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It depends on the type of driving you do. If you do a lot of short commutes--15 miles or less. I would expect that you mpg's would increase. If you are doing longer commutes I would reckon that it would decrease a bit, I would say by 3-5% over the long run. That would be vice convention vs synthetic. Since you are already using a synthetic I would say less than 3% difference either way.

 

[Al]

quote:

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Originally posted by msparks:

quote:

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Originally posted by Giles:
Maybe I wasn't clear, I expect gas mileage to get worse going to 0w40, but by how much?

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It depends on the type of driving you do. If you do a lot of short commutes--15 miles or less. I would expect that you mpg's would increase. If you are doing longer commutes I would reckon that it would decrease a bit, I would say by 3-5% over the long run. That would be vice convention vs synthetic. Since you are already using a synthetic I would say less than 3% difference either way.

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I totally agree. Highway will be less, but you may not be able to see it on your calculations due to lots of variables (weather, amount of traffic, tire inflation, driving habits, etc).

 

[vvk]

quote:

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Originally posted by Giles:
vvk, I find it surprising that fuel economy actually improves for you! Were you using a 10w30 or 5w30 synthetic before switching to 0w40?

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This has been noted for *not* new SAAB 900 engines, both 2.0 and 2.3. I am not the only one, check out NG900 board on saabnet.com.

Details. I have been running Mobil 1 10W-30 in all my SAABs for many years. After reading about people improving gas mileage by switching to xW-40, I decided to try it. My ritual consists of bi-annual oil changes with an annual "short" change intended to clean up the engine. I usually use a 10W-30 non-synthetic for this and run it for a week. This time I filled up with 10W-40 Chevron non-synthetic. Immediately I calculated a 10% improvement during the week I had the oil in. I went on a long trip to Canada, so the calculation is averaged over about 1100 miles of mostly rural highways (I avoid toll roads like plague.)

Then I did another change to Lubro Moly 5W-40 and the fuel mileage is currently 10%-15% better in my regular commuting than it was with Mobil 1 10W-30. My daily routine is all highway, with moderate traffic. Lots of long trips on weekends.

In addition to better fuel economy, I noticed much smoother and quieter engine, which is a good sign. I also tried 10W-40 in my Subaru Impreza 1.8 with very similar results, except I am not conclusive on the fuel mileage. But the engine seems just *so* much happier with the 10W-40 -- silky smooth and very quiet. I still use 10W-30 in winter, though. Can't use 5W-30 in this car -- I get bad lifter noise. No such problems in my other Impreza with a 2.5l engine. 5W-30 year around up until now but I think I'll try 10W-40 or 15W-50 this summer.

 

[dragboat]

quote:

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Originally posted by Giles:

If a car started out at 5w30, at what point do you think it could benefit from xxW40? You mentioned 150,000 miles but it seems to me that it could happen much earlier than this, say at 75,000 miles. [/QB]

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When it started using oil,making noise on start up and or sounds loose at idle when warm in comparison to how it was when new would be a few things to look for when thinking of running a higher vi oil.

I see these posts and the younger folks seem to forget the old way of changing oil for the seasons,synlubes or not.Some think the newer oils will do the job all year round in any motor,anyclimate. IMO way too much has been spewed around about the VII's and the HUGE

spread in the 10/40 oils. Modern VII's used in good branded dino's are up to the task during summer months.Changing oil for the seasons is a good way for better motor longetivity. We all live in different climates,use different vehicles in a variety of ways,,this forum is a great way to post and ask questions about different needs of a owner.
Another problem I see is the first post is asking about a oil but the vehicle/engine and most times place it lives in is not listed so 6 posts down the thread starts to come together.
I am certain opinions will vary

 

[Mike Thompson]

quote:

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Originally posted by TooSlick:
Comparative viscosities with a bulk oil temp of 104F:

M1, 0w-40 --- 80.3 Cst
M1, 5w-30 --- 53.7 "
M1, 10w-30 ---61.3 "

Any questions?

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TS, where did you find the graphs/charts with temp/Cst plots?
Mike

 

[Patman]

Dragboat, you may be onto something. When I'm done testing out the longevity of 10w30 Schaeffer oil, I may start trying out the 5w30 Supreme 7000 in the winter and then 15w40 in the summer.

 

[Giles]

quote:

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Originally posted by msparks:
It depends on the type of driving you do. If you do a lot of short commutes--15 miles or less. I would expect that you mpg's would increase. If you are doing longer commutes I would reckon that it would decrease a bit, I would say by 3-5% over the long run. That would be vice convention vs synthetic. Since you are already using a synthetic I would say less than 3% difference either way.

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I usually do 10 mile commute but also live in moderate temperatures. I'm assuming you are basing this on the 0w being thinner when cold right? I don't live in cold climate so the viscosity of the 0w40 still might be higher during the warm up period than the 5w30 negating any efficiencies. My guess is for the 10 mile trip or less they are probably equivelant. My vehicles gets poor gas mileage during the warm up period as noted on the trip computer (running rich and not using overdrive).

[ January 10, 2003, 12:21 PM: Message edited by: Giles ]

 

[TooSlick]

Giles,

Mobil 1, 0w-30/5w-30/10w-30 are 9.7-10.0 centistoke oils @ 100C, compared to 14.6 Cst for the 0w-40. I'd expect a reduction in fuel efficiency of about 2% from this - particularly for a high revving engine. The viscous losses associated with running a heavy oil are greater at higher rpms. I'd even expect a reduction in fuel efficiency in short trip driving with the 0w-40, due to the shape of the viscosity/temp curve - it crosses the curve for a 5w-30 soon after the engine is started and the 0w-40 is thicker for most of the warmup period. Compare the viscosities of the Mobil 1, 5w-30 and 0w-40 @ 40C and you'll see what I mean. It does not take long for your average oil temps to get above 104F and there are localized heating effects in the bearings as well.

If you have an older pushrod engine that runs at very low rpms, you may not see any significant difference in fuel efficiency.

As a general rule of thumb, car engines that run at high rpms and/or have tight bearing clearances perform better with low viscosity oils. Engines that run at low rpms and heavy loads - like diesels and big block V-8's - do better with thicker oils.

FORGET the analogy of high rpm motorcycle engines that call for 10w-40/15w-50/20w-50 oils. Air cooled motorcycles engines run very high oil temps - often >250F - and wet clutch Japanese motorcycles shear the oil badly; hence both call for heavier oils. The heavier oils are also better suited for dual use as transmission fluids as they cushion the gears better.

It has always been my contention that the lube requirements of an engine change as the bearing and valvetrain clearances open up due to normal wear. Even an engine designed for a 5w-30 oil would probably do better with 0w-40/5w-40/10w-40 once it has 150k-200k miles on it ....You could even use a 15w-40 in this 5w-30 speced engine in mild to hot weather. You will get better compression in a worn engine with the 40wt oil, which will offset the increase in viscosity ....

TS

 

[TooSlick]

Comparative viscosities with a bulk oil temp of 104F:

M1, 0w-40 --- 80.3 Cst
M1, 5w-30 --- 53.7 "
M1, 10w-30 ---61.3 "

Any questions?

 

[Giles]

TS, thanks for the info. I've looked at those specs also and the 0w40 and 5w30 stays the same percentage apart at both the 40c and 100c temps so not too surprising. This is what made me want to see what the effects of this viscosity are on fuel economy based upon peoples experience.

I agree with you that the oil needs of the engine change over the life based upon normal wear. The car makers don't seem to want to specify a single oil now regardless of temperatures or age on the vehicle. Why would we need all of these "Maxlife" type oils if they weren't solving a problem with well worn engines.

If a car started out at 5w30, at what point do you think it could benefit from xxW40? You mentioned 150,000 miles but it seems to me that it could happen much earlier than this, say at 75,000 miles.

 

[TooSlick]

Mike,

Take the data @ 40C and 100C, which is normally given and run a straight line through these two points. In fact, the relationship between viscosity/temp is nonlinear, ie it's a curve and not a straight line. But you can use this approximation to get rough data on flow properties, as long as you don't go too far below 40C or too far above 100C. It is pretty obvious from looking at the 0w-40 and 5w-30 numbers that the 40wt oil is thicker most of the time. You really have to go to 0w-30 or 0w-20 to get an edge on a 5w-30 synthetic in terms of low temp properties ....

The data I posted is from 3w.mobil1.com

TooSlick