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Old 08-15-2006, 05:46 AM   #1
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Using heavier viscosity oil to increase fuel economy?

Has anyone tried using a higher viscosity oil and saw any mileage differences. I've taken the advice of Louis LaPointe's article on www.lubedev.com and switched the 5w30 oil that my Saturn had that I bought in June and switched it to 20w50 (Walmart SuperTech for testing right now) and my gas mileage has increased. Over the past 4000 miles on the 5w30 the best I could get was just under 38 mpg. With 20w50 over the past 1500 miles, my gas mileage has increased to 40 mpg. Pumping up the air in my tires to 44 psi, this week's mileage is 41.2.

I haven't changed my driving habits and drive this vehicle mostly on the highway. It doesn't burn or leak any oil so I didn't switch to the thicker oil for that and I haven't noticed any power loss due to the heavier oil.

I've tried the same thing in my F150 but instead using 10w40 and achieved the max mpg I got with synthetic 5w30 the first two weeks after changing the oil (22 mpg) . And this was having the cruise control on 64 instead of 59 where I usually keep it. Hopefully I will change to 20w50 this weekend if time permits and see what results I get.
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Old 08-15-2006, 07:15 AM   #2
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I'm skeptical.

In the quest for improved FE, the goal of changing your motor oil is to reduce friction. The less energy you waste on heating mechanical components (including fluids) the better. So the better the lubricating properties of the oil the better since they reduce metal-on-metal friction.

**BUT**

Friction is not just caused by metal contacting metal. Friction (and energy loss) also exists in fluids. Viscosity measures a fluid's resistance to shear forces. Higher viscosity = more resistance = more energy required to move it around. By definition, a higher viscosity oil requires that your engine use more energy to make those parts move. Higher viscosity oils are appropriate for mechanical components with wide tolerances, but generally are not appropriate for newer automobile engines that are much more tightly machined than in the past. You want to use the grade that is recommended by the manufacturer, as that's what the engineers know will work.

So I don't understand why anyone would recommend higher viscosity for fuel economy. Rather, what you want is higher lubricity, which measures how well a fluid reduces friction between two sliding components. In general, this means switching to a high-quality synthetic of the recommended viscosity which will exhibit more consistent properties over time due to increased resistance to chemical breakdown.
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Old 08-15-2006, 09:06 AM   #3
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Thanks for your insight. I was skeptical too which is why I tried using the higher viscosity oil. I also plan on trying it on my 97 F150 which currently has 10w40 in it (Always had 5w30 before as per the owners manual (funny, Ford recommends 5w20 now)). I guess the gain in lubricity is outweighing the pumping loss of the higher viscosity oil?

Anyway with no disrespect, isn't this forum for trying new things and sharing new ideas? I'm sure half of the modifications I have read would not be considered a "manufacturer's recommendation".
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Old 08-15-2006, 09:16 AM   #4
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Trying stuff is wonderful, but keep in mind it's also very difficult to conclusively equate a small change in mileage to a single factor through tank-to-tank testing.

For those who want to read the source, can you post a direct link to the info that suggests using a higher viscosity oil to increase efficiency?
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Old 08-15-2006, 09:41 AM   #5
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http://www.lubedev.com/smartgas/ultra5.htm

There are also several articles on the lubedev website, which pretty much covers the same tips.
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Old 08-15-2006, 10:12 AM   #6
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If you tally everything up, the total "percent boost" if you do everything should be 95-195%. That would bring my car up from the stock EPA estimate of 28.5mpg combined to 56-84mpg combined. Going by the raw numbers instead would put me at 49-71mpg So...does that pass the sanity test?

I'm sure some of those things do help somewhat, but I get the impression that not much actual research has gone into their claims. But thanks for the link just the same.
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Old 08-15-2006, 10:34 AM   #7
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This guys stuff comes up over and over and over agian, mainly his claims with acetone.

Nobody I've seen has ever taken a stock vehicle, and then followed his items step by step and reported results.

His opinion on the heavier oil is based on some lubricity tester he created.

I ran heavier oil in my truck than recomended, things were okay, but at certain points the engine felt held back under acceleration, i'm assuming the crank whipping through the heavier mix was slowing it down. And that's the problem IMO, that even if the cylinder is dragging less due to increased "lubricity" (we're assuming here) then somewhere else there will probably be more drag due to the oil weight.
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Old 08-15-2006, 11:00 AM   #8
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oil

Lighter oil takes less energy. Why would automakers try to put the lightest oil in their vehicles? It is because with a lighter oil, the parts can move more freely. For example: my boss' work truck has 5w30 in it. (Chevy Silverado V-6)
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Old 08-15-2006, 11:18 AM   #9
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I've run 20w-50 with no change in FE. I agree with Metro tank to tank varibility is a killer. Different cars behave differently but the only things on that site that have worked for me have been slowing down and driving technique.
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Old 08-15-2006, 11:55 AM   #10
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the main thing I can see with heavier oil is that it is going to help the rings seal better, increasing compression in an older engine, from what I've been told, you want to run the lightest weight oil that still maintains oil presure (without a gauge this is hard to do), to light of an oil and it flows out of the bearings to fast, and you loose that cushin that prevents metal to metal contact.
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