Fuel Economy Gains for Different Weight Oils

[Gene K]

We have discussed several times in the past the gains in fuel mileage that can be expected from different weight motor oils.

While wading through the NHTSA site I found a list of various technologies planned to meet the tighter Light Truck CAFE standard in 2005-2007. I assume the reference oil was 10W-30.


1% 5W-30
2% 5W-20
3.1% 0W-20

Gene

 

[KW]

I wonder why the big differance between the 0W20 and 5W20? These oils should be just about the same thing unless they were testing the oil on the north pole.

 

[Gene K]

I assume most of the gain was seen in the warm-up cycle. Of course it correlates pretty well with the gain seen going from 10W-30 to 5W-30. All in all going from 10W-30 to 0W-20 on your entire line-up would improve your truck fleet average from 21.0 mpg to 21.65 mpg. Remember this is about the EPA test cycle more than the real world.

Gene

 

[n8wvi]

I went from 5w-30 to 15w-40 and GAINED about 2MPG.

Dave

 

[VaderSS]

Went from 20W50 to 10W30 in the Festiva and picked up about 3%.

 

[Gary Allan]

I've never noticed virtually any difference between various weights. Then again, my engines aren't economy nor performance (revvers) oriented. My 4.0 jeep engine did see a solid 1.5 fuel eco increase when I switched to Delvac 1 ..but it returned to normal after about 5k. Since I'm into XOCI (currently going for 12.5k) ..does it really matter?

I think that lighter engines that develop most of their power in the upper rpm ranges can take advantage of these lighter weight lubricants. The average 4 or 6 banger barely has enough power to idle ..and typically isn't even breathing heavy(developing fuel comsuming power) until the upper rpm range. Hence, IMHO, they shave factional hp frictional losses under normal operating conditions. My 4.0, OTOH, has its full torque peak realized @ 1800 with a sharp upramp from 1200. That is, the only fuel savings is in reducing the rpms at typical speeds. Power doesn't come from nowhere. That leads me to conclude that most of my fuel consumption (per rpm) is occuring just about off idle and in any practical use of the engine.

 

[Gene K]

quote:

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Originally posted by VaderSS:
Went from 20W50 to 10W30 in the Festiva and picked up about 3%.

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Going to try 0W20?

Gene

 

[VaderSS]

Thinking about it... **** , if it trashes the engine I'll just drop a Mazda B6 in for 20 more HP.

 

[Gene K]

quote:

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Originally posted by VaderSS:
Thinking about it... **** , if it trashes the engine I'll just drop a Mazda B6 in for 20 more HP.

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There is actually a Festiva here in town with a BP (1.8L DOHC 130 bhp) from the Escort GT swapped in.

Gene

 

[Robbie Alexander]

Okay, but what was the milage?
How clean was the internals?
With a little wear in the internals, I could see this for SURE.

quote:

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Originally posted by n8wvi:
I went from 5w-30 to 15w-40 and GAINED about 2MPG.

Dave

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[Tim]

I switched my TDI at about 30,000 miles from Amsoil 10W-40 to Amsoil 15W-40. My mileage has increased from an average of 56mpg to 58mpg.

I don't think this increase is as significant as the fact that my mileage didn't go down.

Viscosities at 100C and 40C for the 10-40 vs 15-40 are:

14.9 / 15.5 and 90.5 / 100.2

So the 15-40 is thicker at temp as well as at ambient...


FWIW


Tim
edit due to messed-up number

 

[huffmuds9320]

So some get better fuel economy by using thicker oil like 15W-40? It seems that a thicker oil will drop your gas mileage a bit. I've used 5W-40, 5W-30 synthetic and now using 5W-30 conventional and noticed no difference between the three. I get about 19-20mpg city on my '02 VW Jetta 2.0 and 22-25mpg for mixed driving.

 

[Gary Allan]

quote:

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It seems that a thicker oil will drop your gas mileage a bit.

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IMHO only to the limit of the difference in the hp it takes to pump it through the engine. If you're driving 75-80 mph or driving in intown traffic ..the diffence is negligable compared to the other consumptions of hp (like overcoming wind resistance or moving from a standstill). It might do something if you were John or Jane Q. super citizen and drove 55-60 and exercized all the recommended economy techniques ...or were performing a CAFE test cycle

 

[SteveD2]

It's a simple fact that thicker oil means less gas mileage in ANY engine. Thicker oil takes more energy to move around, doesn't matter what engine it's in. Some engines may have a noticeable difference in mileage, some might be .0001mpg, but it WILL lower your mileage. If you get better mileage going to a heavier weight, there are other factors involved. Simply going to a thicker oil will not give you better mileage, that would be against the laws of physics.

 

[Sin City]

Some old data from Honda lists a fuel economy gain of 1.5% when using Honda brand 0W-20 motor oil in place of Honda's 5W-30 motor oil in one of their OHC 2.0L engines.

I don't think it will be very long before nearly all new gasoline powered vehicles in North America will be using 0W-20, 5W-20 or 0W-30 motor oils. I also think the "heavy duty" diesel marked will change within the next few years to either 10W-30 or 5W-40 motor oils for new engines.

 

[Al]

quote:

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Originally posted by n8wvi:
I went from 5w-30 to 15w-40 and GAINED about 2MPG.

Dave

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Data from one particular vehicle with no real controls which take account for variables will not give statistically valid results. So its really highly, highly that the increase you see is bc of the thicker oil. Something in your comparison skewed the results somehow.

The link between thinner oils and lower energy requirements has been proved time and time again in fleet tests. And in industrial oils economy has increased when say switching from an ISO 46 to ISO 32 oil

Not slaming your conclusions. But the only way economy could increase with a heavier is if the heavier oil provided partial or full film lubrication when there may have been destructive metal to metal contact with the thinner oil. Not saying that is impossible - but highly unlikely.

 

[Pablo]

I gotta be honest........it doesn't SEEM to matter what oil I use....if there is a change in MPG it must be in the noise. IOW other factors (including fuel brand/type) change the MPG a heckofalot more that oil vis.

The SINGLE thing I did to a car (less engine replacement) that made the biggest delta? I physically swapped out the AT for a manual tranny. Overnight I went from 17-19 (never over 20mpg) to 24-25 mpg (28 if I go easy on boost)....not that this is very practical and NEW cars seems to have really bridged that AT-MT gap.....

 

[VaderSS]

Don't know why anyone would debate this. Think the EPA is pushing thinner oils for no reason? I admit that I saw no change in economy in the Impala when switching from the near 20 weight Mobil 1 10W30 to 0W40, but then a 3% increase would show little on a car that averages 16MPG annually and experience extremely varied circuits. If I had stayed with it a year I'd of probably seen the .5MPG decrease, but one interval was not enough to really get past the noise. 3 tanks with a solid 1 mpg increase from 33 to 34 on the Festiva though, with a cycle that does not really vary from week to week...

I also feel that operating RPM has something to add, with the Impala turning over 2500 at 90 and the Festiva turning over 3600 at the same speed. Plus, on average the RPM stays higher in city driving with the Festiva as it's engine is much more stressed with a 32Lb-HP loading vs the 15 for the Impala.

quote:

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Originally posted by Gene K:

There is actually a Festiva here in town with a BP (1.8L DOHC 130 bhp) from the Escort GT swapped in.

Gene

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Only problem there is A/C compressor won't fit. That's not an option... If I want to, I can easily get 100 HP out of a B6 and that should be plenty to motivate a 1700Lb car. Heck it ain't too bad with only 62. Would be nice to have 15Lb-HP in the Festiva though...

 

[Gary Allan]

quote:

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Don't know why anyone would debate this. Think the EPA is pushing thinner oils for no reason?

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No one really does debate it. It's good energy policy. If you do a poll, however, you'll see that typically after the mainstream adoption of 5w-xx oils ..the OEM manufacturers raised the typical PSI on the engines ..somewhat negating the effects. Sorry PSI equates to resistance in anyones book. But let's not diverge from the main issue.


Thinner oil is like some Indy car shaving oz. off of the unsprung wheel assmebly to get more out of what you're producing...while the variables that YOU introduce to your daily drive can add POUNDS.

Not many here drive "economy runs". That is, just about everyone drives without their wallet as a guideline beyond they don't want to spend anymore than they have to ..to do what they're doing. They still drive 75-80 ..even though they're fully aware that the wind resistance increases by the square ..they still are "spirited" in their urban driving.


That is, how much is a .25-.50 hp reduction going to compare to the 5-7 that you waste just being "you".

 

[n8wvi]

That was my first thought as well, although previous UOAs indicated the engine was running just fine. Also, I never lost even half a quart over 5,000 mile OCIs, which to my uneducated mind means, again, everything (ring/seal/blowby wise) is running fine.
I'm not saying I know what the answer is, I don't; I'm just at a loss.

Dave