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Old 05-07-2022, 12:04 PM   #1
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Can different engine oils effect miles per gallon?

Wondering if any of the good folks on this forum have experienced a notable increase or decrease in mpg after switching different brands or even different viscosity oils for your diesel coach engine? Have seen this occur in gasoline engines in cars and trucks. Also wondering if changing to synthetic 15-40 diesel might effect mpg. Stay Safe.
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Old 05-07-2022, 02:44 PM   #2
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I'd read that it's widely accepted that changing to synthetic will give you a slight mileage increase. I remember reading that 2-3 times a few years ago but can't give you any links.
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Old 05-07-2022, 02:53 PM   #3
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New car manufacturers are now specifying 5W20 or even 5W15 oil. Lubrication properties have improved, and they can get away with thinner oils which definitely improve mileage.

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Old 05-07-2022, 03:00 PM   #4
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Went to 5w40 Shell T6 from Shell 15w40 mineral and did notice a slight MPG gain over a long haul (3000 miles). Although in saying that so many variables come into play. Weather, driving speeds, time of year. Lets face it we will never put enough miles on these units to wear them out so oil choice is just that ,, your choice.

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Old 05-07-2022, 03:07 PM   #5
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Quote:
Originally Posted by greeneville1 View Post
Wondering if any of the good folks on this forum have experienced a notable increase or decrease in mpg after switching different brands or even different viscosity oils for your diesel coach engine? Have seen this occur in gasoline engines in cars and trucks. Also wondering if changing to synthetic 15-40 diesel might effect mpg. Stay Safe.
What oil does the engine manufacturer recommend for your coach? Is the engine still under warranty?

I use what the engine manufacturer recommends, primarily because I’m more concerned about the longevity of the engine than I am about getting an additional 2/100ths of a mile out of a gallon of fuel.

Drive 5-10mph slower than you normally do if you want to see a notable increase.
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Old 05-07-2022, 03:12 PM   #6
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IMO, changing from engine manufacturer's oil recommendation (specs and viscosity) in the HOPES of gaining a few tenth of a MPG is a very BAD idea.


No question, speed and the driver are the two most significant influences on MPG.
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Old 05-08-2022, 05:12 AM   #7
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Agree wholeheartedly with Wolfe10.

For those that drive with a software performance monitoring system, it is quite evident the fluctuation in MPG given the envirormental conditions, terrain and most importantly, the miles per hour.

Fuel consumption wise, my coach with towed serves me best at 62 mph and if it is real windy, 60 is my best friend.
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Old 05-08-2022, 06:20 AM   #8
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The manufactures use thinner oils for tiny increases in MPG for the whole category of vehicles, in an effort to meet the EPA requirements.

I don't think it would even be measurable, in one engine.

Slowing down saves gas.
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Old 05-08-2022, 09:25 AM   #9
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The manufactures use thinner oils for tiny increases in MPG for the whole category of vehicles, in an effort to meet the EPA requirements.

I don't think it would even be measurable, in one engine.

Slowing down saves gas.


Slowing down is very correct. Although I just have problems doing it. LOL.
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Old 05-08-2022, 09:51 AM   #10
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back in the late 70's when Mobile-1 came out. That was part of the sale pitch "improve mpg". I used it then and saw maybe 1/5 mile improvement per gallon. Or was it, I wanted to see it and changed my driving habits? Im thinking that the improvement is during the warm up. The oil performs better.
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Old 05-08-2022, 09:53 AM   #11
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Where this idea comes from is from companies with fleets of semis, I believe. Those trucks can often rack up millions of miles and it's easier to see a slight advantage to synthetic with 100's of trucks and 100's of thousands of miles traveled.

But as said, you'd likely get a larger increase in mileage by slowing down. And those that haven't done it yet, adding things like Eco-Fins, V-Spoilers, or AirTabs to the rear edge of your RV will get you a solid 5% increase in fuel economy. And get you more stability when big trucks or buses pass you on the freeway or a country road.

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Old 05-08-2022, 10:05 AM   #12
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The main feature of engine oil that can affect MPG is its viscosity. A high viscosity oil requires more energy to churn it around so it will result in a slightly lower MPG. Switching to a synthetic can improve your MPG because you can get away with a lower viscosity oil. The reason you can get away with it is because synthetics have a much higher viscosity index, meaning that as the engine heats up the oil doesn't thin out as much as a straight mineral oil, i.e., it maintains its viscosity over a greater temperature range.
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Old 05-08-2022, 11:58 AM   #13
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Correct. the federal acronym is CAFE: Corporate Average Fuel Economy. It varies for different classes of vehicles. that's why the Plymouth PT Cruiser was actually certified as a "Light Truck" since light trucks have a lower CAFE number.

Quote:
Originally Posted by twinboat View Post
The manufactures use thinner oils for tiny increases in MPG for the whole category of vehicles, in an effort to meet the EPA requirements.

I don't think it would even be measurable, in one engine.

Slowing down saves gas.
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Old 05-08-2022, 01:11 PM   #14
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Originally Posted by joeplazek View Post
Went to 5w40 Shell T6 from Shell 15w40 mineral and did notice a slight MPG gain over a long haul (3000 miles). Although in saying that so many variables come into play. Weather, driving speeds, time of year. Lets face it we will never put enough miles on these units to wear them out so oil choice is just that ,, your choice.

joe
I have a car that uses 0W20. Why not give that a try?
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