Fuel mileage getting worse…..

[Corporate72]

Got a 2021 chevy custom, was getting wicked mileage, bout 750 kms to a tank! Which i thought was pretty good, now ill be lucky to get 550. It has 21000 kms on it. Anyone else have a similar experience??

[Grumpy Bear]

Pretty normal winter behavior. Here is about 4 years worth of tank by tank on my truck. Peaks are summer, dips are winter. Most of the loss is oil drag not 'winter fuel'. Pretty big swing as you can see. 

 

[Corporate72]

12 hours ago, Grumpy Bear said:

Pretty normal winter behavior. Here is about 4 years worth of tank by tank on my truck. Peaks are summer, dips are winter. Most of the loss is oil drag not 'winter fuel'. Pretty big swing as you can see. 

 

Jeez eh, thats some mean drops in mpg for sure! Not even winter yet and its getting bad! 0w30 goin in i guess already lol

[Grumpy Bear]

This will give you an idea. Note that even at 15 C (59F) vs 30 C (90F) the difference in low temperature viscosity is huge. 

 

 

Typical 0W30

 

 

Straight 30W

 

 

[Grumpy Bear]

Note as well that by the time your oil is 60C (140 F) the difference is nearly nil.  This one is interesting as well. Even the with the same first number 5W the low temperature performance is quite different and a low first number is not always a good indication. Look for a low Cold Cranking Viscosity in the GRADE you are look at. First number, not second. The SAE sets a high value only on this spec. Performance from oil to oil varies widely. 

 

Edited November 6, 2021 by Grumpy Bear

[Corporate72]

On 11/5/2021 at 7:34 PM, Grumpy Bear said:

Pretty normal winter behavior. Here is about 4 years worth of tank by tank on my truck. Peaks are summer, dips are winter. Most of the loss is oil drag not 'winter fuel'. Pretty big swing as you can see. 

 

So howdoes a guy read this graph im confused

[Grumpy Bear]

18 hours ago, Corporate72 said:

So howdoes a guy read this graph im confused

Each dot is the hand calculated MPG for that tank read from the vertical scale. The bottom is which data point. You see how it moves with the season. Top clusters summer, bottom winter. About four years worth. I could add trend lines if that would help with the visualization. 

[shakenfake]

But what are the bottom numbers? Is that days in a year?

[redwngr]

3 hours ago, shakenfake said:

But what are the bottom numbers? Is that days in a year?

I believe that is the fill number.

Each fill is a data point.

 

About 325 of them.

 

[Grumpy Bear]

1 hour ago, redwngr said:

I believe that is the fill number.

Each fill is a data point.

 

About 325 of them.

 

 

Bingo! 

[shakenfake]

Ah 

[BigBadSierra]

Yes these motors hate winter gas mix. Plus I take the pretty rims and wheels off and put on the stockers with Duratrac's.

 

So I see a bigger drop yet.

[Another JR]

Think about this. What fraction if your operating time is spent with the oil temperature below the stabilized operating temperature, which is pretty much the same regardless of outside air temp due to the cooling system thermostat?  To what extent does “oil drag” compare to your total actual engine power output needed to move the vehicle?  A few percent?  So how much difference does even a large change in cold oil drag really make in overall fuel mileage? How does that compare to the several percent change in volumetric heating value of the fuel when they change to the winter fuel formulation, recognizing that fuel is sold based on volume?  
 

To say the seasonal mileage effect drivers see is not dominantly driven by the fuel characteristics doesn’t make sense to me. 

[customboss]

BTU delta between US regional blends for winter vs summer is ~ 1.7% less energy content.  Canada follows US EPA regional blends but not always.  

 

Alberta/Edmonton is cold and stays cold normally so that certainly plays but I am going to assume you didn't see this big of a drop last season? 

 

27% drop in average fuel efficiency has me thinking its more than seasonal IF YOUR UNIT IS WELL TUNED.  

 

What fuel do you use?  If you have access to Canadian CO-OP gasolines try a tank of regular to compare to the cheaper stuff you might be running. Let us know if their formulation helps.  They use similar additives that CENEX, CountryMark, AgriMark, and other CO-OP centric formulators and refineries use in the US.  They also formulate and blend some great engine oils. 

 

https://www.fuel.crs/consumer/detail/top-tier-gasoline

 

If you are already using their formulations then you have another issue or its just colder than before. 

 

 

 

 

[Another JR]

I personally have not experienced such a large drop in mileage in the winter, but I am in the PNW, which has mild winters. 
 

I was under the impression that the winter fuel blend here has ethanol at approximately the 10% limit, where the summer fuel has much less ethanol. Wouldn’t that much of a difference in ethanol content cause an energy density change greater than 1.7%?