Could 1.5 cST Extra Cause 2.5 MPG Loss ?

[Fallguy]

Old 5w30 dino I used typically sheared down to 8.9 in short order, new 5w30 synthetic I use is 10.5 and likely stable?

Use to get 32.5 to 33mpg on highway quite frequently.

Now seam to get 30 to 30.5 tops.

Think a 1.6 increase cst could be the culprit? Pretty new vehicle, nothing else changed.

 

[Shannow]

I've seen thinner oil drop mileage.

 

[HTSS_TR]

Winter gasoline is known to reduce gas mileage by about 2-3% or more, also colder climate tends to reduce gas mileage by 2-3%, specially during warm up miles and it takes a lot longer to get the oil up to operating temperature to have the most optimal gas mileage.

 

[beast3300]

I blame winter gas.

 

[gathermewool]

I replaced Rotella T6 5W-40 with Amsoil SSO 0W-30 just before filling up. >2cSt thinner at temp, and probably thinner at every single temperature point, but I recorded average MPG last tankful and I'm 0.6 MPG down after a quarter tank on this, the second fillup.

 

[Mr Nice]

Originally Posted By: Shannow
I've seen thinner oil drop mileage.

Yup, me too.

 

[Pablo]

I doubt some of these wild swings in MPG have much to do with oil choice.

 

[oggb]

I get ~21 mpg city and ~29 mpg highway no matter what oil I run - 5w30 dino, 15w40 dino, 10w-30 blend, 5w30 synthetic, 5w-40 synthetic.

I even get the same mileage using a 75w-140 in my rear diff vs. using an 80w-90.

I got the same gas mileage after swapping out my wheel/tire combo with a new set of wheels/tires that saved me about 7lbs per corner.

I get the same gas mileage whether I run my tires at 28 psi or 42 psi.

WHAT AM I DOING WRONG!?

Guess I oughta try some 0w-20 Mobil 1 AFE.

 

[JOD]

Originally Posted By: Pablo
I doubt some of these wild swings in MPG have much to do with oil choice.


Agreed.

I think a lot of folks vastly underestimate the impact of the other variables which factor into fuel economy. Even in a controlled environment, calculating energy usage is difficult; getting in your car and driving, then tracking your fuel usage?? You better have a lot of data to suppress the noise...

All else equal, thinner oil has less friction and will offer marginally better fuel economy--but the difference is so small that it's not going to be easy to measure under the best of circumstances.

 

[Audi Junkie]

Some oils have more friction modifiers, which do wear out, but this is not your problem.

 

[bullwinkle]

+1-driving style, tire pressure, loads carried, winter fuel, even headwinds & A/C use have a bigger effect than thin oil. You may have even picked up a tankful of gas that had too much ethanol in it! The thin oil will help a little, but many things help MPGs.

 

[deven]

Do you know the HTHS of these said oils? That and combination of winter fuel may be the culprit for ya.

 

[Fallguy]

Thanks all did not think the +1.5 cst alone would explain it.

Broke the car in on 5w30 Quaker State Dino which typically thins to 9.0cst quickly (or did for me via last UOA in a different vehicle).

Now running 5w30 Synpower which is 10.5 cst I believe.

But is also colder now, fuel blend may also have changed etc.

Regards,

 

[Loobed]

Originally Posted By: LT4 Vette
Originally Posted By: Shannow
I've seen thinner oil drop mileage.

Yup, me too.



+1

Also check tire inflation.

 

[demarpaint]

I'd say winter gas and under inflated tires could be responsible. Engines run richer and idle faster for a longer periods of time during the winter as well. Add everything up and it is easy to see fuel economy drop off during the winter. JMO

 

[GMorg]

At cruising speed on a flat drive, wind resistance or drag is the major energy expense for your vehicle. At a fixed speed (relative to the wind), the density of the air is directly proportional to the amount of energy that you need to displace that air. Air density increases about 0.2% for each degree Fahrenheit that the temperature drops. So, based on temperature alone, drag can increase 10% from 80F to 30F or 20% from 80F to -20F. Fuel formulations, reduced tire pressure, and oil viscosity can affect fuel consumption, but 5-20% efficiency loss in the winter is to be expected from mother nature alone without any considerations for maintenance choices or regulatory agencies.

It is hard to break those pesky laws of physics.