How much does oil viscosity really change mpg?

[CharBaby]

Just changing oil grades by themselves, I’ve never noticed a single gain/loss in MPG in winter or summer in any vehicle we’ve owned. I think that a lower oil grade in addition to all the other benefits that the manufacturer puts into the automobile…or removed from the automobile. Such as lower overall & unsprung weight, better aerodynamic, fuel saving devices, engine/transmission designs, tires, etc.

I’ve put on lower rolling tires(not dedicated LRR), lower grade oil(from 5w30 to 0w20), removed roof racks and extra weight/junk in the trunk all at the same time and didn’t notice enough fuel economy gain to mention.

I have also loaded my vehicle to the hilt on a family vacation driving from NY to FL and back and have gotten among the better MPG figures in that vehicle ever.

 

[ZeeOSix]

It’s not that MPG isn’t important to me but more wondering why the drastic change in oil recommendations lately and who they’re recommending them for. I truly find it interesting. Personally I don’t want the govt ever driving the industry. I believe competition breeds excellence.

In the background, there is a slight competition factor lingering ... that is, if one manufacture can claim a better EPA fuel mileage rating on the window sticker than another because they are designing to, and specifying a thinner motor oil, then that might be a good thing for selling a vehicle to someone who considers fuel mileage a big factor. But of course the main factor of the automotive industry being driven by CAFE is to use thinner oil is to help reduce emissions into the atmosphere. A lot of engine systems technology is driven and has changed for the same reason. On a large scale, it can make a difference. Can you imagine what it would be like if everyone was still driving around in cars made to 1960s technology in terms of emissions? Have you ever gotten behind some old 1960s/1970s car and your eyes are literally burning from all the raw gas fumes from the exhaust?

 

[edyvw]

In the background, there is a slight competition factor lingering ... that is, if one manufacture can claim a better EPA fuel mileage rating on the window sticker than another because they are designing to, and specifying a thinner motor oil, then that might be a good thing for selling a vehicle to someone who considers fuel mileage a big factor. But of course the main factor of the automotive industry being driven by CAFE is to use thinner oil is to help reduce emissions into the atmosphere. A lot of engine systems technology is driven and has changed for the same reason. On a large scale, it can make a difference. Can you imagine what it would be like if everyone was still driving around in cars made to 1960s technology in terms of emissions? Have you ever gotten behind some old 1960s/1970s car and your eyes are literally burning from all the raw gas fumes from the exhaust?

That is why I said that FAR more effective would be to just ban remote starts.

 

[Astro14]

Thank you for the response. I just want to put it out there I’m not here to argue but to learn. For some **** reason I asked one question and it was like lighting a fuse in my brain. I almost wish I went back to knowing nothing and just threw whatever the gas station was selling back in. I guess by trying to understand the industry and why they’re doing what they’re doing I can make better decisions for myself. It’s not that MPG isn’t important to me but more wondering why the drastic change in oil recommendations lately and who they’re recommending them for. I truly find it interesting. Personally I don’t want the govt ever driving the industry. I believe competition breeds excellence. Before this new vehicle I bought I put Shell T6 in everything. But to be honest I knew I wouldn’t keep them forever. This new guy, my grenadier, could very well be my last vehicle. My grandmother, father, and aunt all have had Alzheimer’s at roughly 60 and the odds aren’t good so I bought this thing knowing it could be my last and the aviator in me makes me dig into everything systems related. So once you started responding to a question a while back I found myself debating if I should have gone into petroleum engineering instead lol.

I think I answered it, but I will restate my point - for you, personally, it won’t be measurable. Not accurately.

There are too many other factors. I went up from 0W20 to 5W30. I have tracked every single fill up. My MPG went up with the 5w30 but there were just too many variables for me to isolate the viscosity as a factor. It’s too insignificant in the face of everything else in my driving.

So, yes, a slight reduction in viscosity makes a measurable difference over a fleet, where the rest of variables become noise.

But it makes no real difference for you and your car.

 

[doublebase]

I have not noticed any sort of measurable difference in the two different vehicles I’ve tried it on, then again I only went from a 0W20 to a 5W30…one was in a V6, the other a V8. MPG stayed the same (from what I could see).

 

[kschachn]

In the background, there is a slight competition factor lingering ... that is, if one manufacture can claim a better EPA fuel mileage rating on the window sticker than another because they are designing to, and specifying a thinner motor oil, then that might be a good thing for selling a vehicle to someone who considers fuel mileage a big factor. But of course the main factor of the automotive industry being driven by CAFE is to use thinner oil is to help reduce emissions into the atmosphere. A lot of engine systems technology is driven and has changed for the same reason. On a large scale, it can make a difference. Can you imagine what it would be like if everyone was still driving around in cars made to 1960s technology in terms of emissions? Have you ever gotten behind some old 1960s/1970s car and your eyes are literally burning from all the raw gas fumes from the exhaust?

True, and I agree with that. But unburned hydrocarbons and NOx are more a function of efficient and controlled combustion, whereas what's driving fuel economy is CO2 emissions which do not contribute to smog or foul smelling exhaust. It's strictly related to the amount of fuel that's being consumed.

 

[BMWTurboDzl]

That is marketing BS. Because LL01 can have an HTHS of 3.5mpas, and LL01FE can have an HTHS of 3.49mpas.
What they did is they compared the lowest possible HTHS in LL01FE and the highest possible HTHS in LL01.
That is like when oil companies say: our synthetic oils clean xxx times better than average mineral oil.

Thank you for the response. I just want to put it out there I’m not here to argue but to learn. For some **** reason I asked one question and it was like lighting a fuse in my brain. I almost wish I went back to knowing nothing and just threw whatever the gas station was selling back in. I guess by trying to understand the industry and why they’re doing what they’re doing I can make better decisions for myself. It’s not that MPG isn’t important to me but more wondering why the drastic change in oil recommendations lately and who they’re recommending them for. I truly find it interesting. Personally I don’t want the govt ever driving the industry. I believe competition breeds excellence. Before this new vehicle I bought I put Shell T6 in everything. But to be honest I knew I wouldn’t keep them forever. This new guy, my grenadier, could very well be my last vehicle. My grandmother, father, and aunt all have had Alzheimer’s at roughly 60 and the odds aren’t good so I bought this thing knowing it could be my last and the aviator in me makes me dig into everything systems related. So once you started responding to a question a while back I found myself debating if I should have gone into petroleum engineering instead lol.

Okay so I did some digging this morning. The FE gain is "up to 3%" under the NEDC (New European Driving Cycle) when moving from LL01 to LL14Fe (0w20). In any case when applied towards a fleet of thousands of vehicles it does add up and saves BMW some amount in penalty paid.

https://www.autokaubad24.ee/files/bmw_original_oil.pdf

 

[oil pan 4]

Cummins wrote a paper on this some years ago. If 15w-40 is the control switching to 10w-30 would give a 1 to 2% increase and switching to 5w-20gave about a 3% increase, but then the life of their engines was shortened by up to 1/3.

 

[Ret2]

I'm reading all the BMW specs of LL17FE vs LL01 vs LL04. New BMW engines wanting 0w12 down from 0w20 and before that 5w30/5w40s. So my question is with such a hard push to these light oils what is the real mpg gain? People say it's all because of CAFE laws but what kind of MPG difference would I see if I went from a 5w40 to say a 0w20?

I have a 2022 that is marked for 0-20 oil. 0-20 may be the best choice to squeeze out an extra 200ft from a gallon of gas, but is it the best choice for longevity of my engine? It certainly raises suspicion when the factory service manual specs only 0-20 if you live in the US, but when in Mexico, anything from 0-20 up to go 'ol 10w40 is fine. This is the govt at work.