Fuel mileage getting worse…..

Grumpy Bear · November 24, 2021

On 11/23/2021 at 8:54 AM, Another JR said:

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.

That depends on trip length. I log this stuff. It can take 3 miles to reach operating water temperature but 25 miles to reach 'stable' oil temperature. 10 miles to reach 170 F oil temp. The transmission with an operating thermostat can take 100 miles in mid winter to get hot enough to open the thermostat (194F). Can take as little as 20% of that distance on a 90 F day. Look at this graph again. If your trip lengths are under 10 miles when it is 32 F (0C) or colder your average viscosity is is 10X higher than stabile oil temps. How much extra power does that take. During the warm up idle, if this is your custom and if you have a torque meter you would find it take 2 to 3X more. 10 to 15 hp instead of 4.8 to 5.2 hp.

As shown in another earlier graph even the base oil type the SAE grade is made from has a LARGE influence on the front end (cold) viscosities. Each has it's own curve.

The diffs and wheel bearings never reach summer viscosities and are the heaviest fluids in the system.

Find your self a post on a flat road. Come in at 50 mph and click off the cruise and note how far it takes to slow down to 30 mph. Leave it in gear. Make it a habit and with the seasons you will find perhaps a 100 yard difference in coast down length. If you do this instead using time instead of distance and know the weight of the vehicle you can calculate the difference in fluid drag (assuming you're diligent about tire pressures).

@customboss isn't steering you wrong. The BTU content is 1.7% different. I've made millions of gallons of gasoline sir and he's tested likely more. We are not guessing. These are things we've measured.

Depending on where you live the difference in between summer and winter wind speed and direction is also a HUGE influence in a pickup and the faster you drive the more impact it has. In my area winter/spring winds are continuous and stiff. Walk into a 20 mph wind with a 4X8 sheet of plywood. :crackup: Summer and fall are much calmer here. Heck even crops in a field influence mpg (wind breaks). Wind speed and direction even at 55 mph can and does have a 15-20% effect.

Are you 'all over' tire pressures year around? Com' on now. People hate adjusting pressures anytime but when it's really cold they will suffer the fuel and safety decline. 3 psi is noticeable. 10F a change of 1 psi rule of thumb. This time of year here that can mean a 3 to 5 psi swing several times a week.

There is allot more to winter fuel decline than 'winter fuel'.

Edited November 24, 2021 by Grumpy Bear

Another JR · November 24, 2021

Tha

1 hour ago, Grumpy Bear said:

That depends on trip length. I log this stuff. It can take 3 miles to reach operating water temperature but 25 miles to reach 'stable' oil temperature. 10 miles to reach 170 F oil temp. The transmission with an operating thermostat can take 100 miles in mid winter to get hot enough to open the thermostat (194F). Can take as little as 20% of that distance on a 90 F day. Look at this graph again. If your trip lengths are under 10 miles when it is 32 F (0C) or colder your average viscosity is is 10X higher than stabile oil temps. How much extra power does that take. During the warm up idle, if this is your custom and if you have a torque meter you would find it take 2 to 3X more. 10 to 15 hp instead of 4.8 to 5.2 hp.

As shown in another earlier graph even the base oil type the SAE grade is made from has a LARGE influence on the front end (cold) viscosities. Each has it's own curve.

The diffs and wheel bearings never reach summer viscosities and are the heaviest fluids in the system.

Find your self a post on a flat road. Come in at 50 mph and click off the cruise and note how far it takes to slow down to 30 mph. Leave it in gear. Make it a habit and with the seasons you will find perhaps a 100 yard difference in coast down length. If you do this instead using time instead of distance and know the weight of the vehicle you can calculate the difference in fluid drag (assuming you're diligent about tire pressures).

@customboss isn't steering you wrong. The BTU content is 1.7% different. I've made millions of gallons of gasoline sir and he's tested likely more. We are not guessing. These are things we've measured.

Depending on where you live the difference in between summer and winter wind speed and direction is also a HUGE influence in a pickup and the faster you drive the more impact it has. In my area winter/spring winds are continuous and stiff. Walk into a 20 mph wind with a 4X8 sheet of plywood. Summer and fall are much calmer here. Heck even crops in a field influence mpg (wind breaks). Wind speed and direction even at 55 mph can and does have a 15-20% effect.

Are you 'all over' tire pressures year around? Com' on now. People hate adjusting pressures anytime but when it's really cold they will suffer the fuel and safety decline. 3 psi is noticeable. 10F a change of 1 psi rule of thumb. This time of year here that can mean a 3 to 5 psi swing several times a week.

There is allot more to winter fuel decline than 'winter fuel'.

Thanks for the detailed explanation and for making the extra effort to educate me

Grumpy Bear · November 24, 2021

49 minutes ago, Another JR said:

Thanks for the detailed explanation and for making the extra effort to educate me

No problem. Pay it forward Everyone has something to contribute, right?

nutdriver · November 25, 2021

On 11/5/2021 at 8:34 PM, Grumpy Bear said:

I understand the graph but am having some trouble believing this is in a Duramax. What engine is this? It looks like your average is somewhere in the vicinity of 27 mpg with peak average even more.

Edited November 25, 2021 by nutdriver

Grumpy Bear · November 25, 2021

28 minutes ago, nutdriver said:

I understand the graph but am having some trouble believing this is in a Duramax. What engine is this? It looks like your average is somewhere in the vicinity of 27 mpg with peak average even more.

Oh! Well...It's not a Duramax but the reference is to the effect of oil viscosity on economy with remains valid. More to the point the cold end of viscosity. Sorry, no intent to confuse or deceive.

nutdriver · November 25, 2021

1 hour ago, Grumpy Bear said:

Oh! Well...It's not a Duramax but the reference is to the effect of oil viscosity on economy with remains valid. More to the point the cold end of viscosity. Sorry, no intent to confuse or deceive.

No worries. My experience driving a VW TDI for 20 years showed swings of about 10% between winter and summer. I mitigate the winter hit somewhat by driving my duramax more gingerly until it is fairly warm. I have about 2 miles of 35 mph followed by 3 miles of 60 mph before hitting a local expressway.

redwngr · November 26, 2021

15 hours ago, nutdriver said:

I understand the graph but am having some trouble believing this is in a Duramax. What engine is this? It looks like your average is somewhere in the vicinity of 27 mpg with peak average even more.

What makes you think Grumpy drives a duramax?

I'm pretty sure his truck is a V6 gas...

Fwiw, based on how mine have been I could be convinced it is a 3.0L dmax, but certainly not a 6.6L dmax.

redwngr · November 26, 2021

Lifetime is currently 25.6.

Big dips are towing (less than full tank trips)

I've never plotted any of my 6.6's, but I logged the fills and they

Edited November 26, 2021 by redwngr

nutdriver · November 26, 2021

9 hours ago, redwngr said:

What makes you think Grumpy drives a duramax?

I'm pretty sure his truck is a V6 gas...

Fwiw, based on how mine have been I could be convinced it is a 3.0L dmax, but certainly not a 6.6L dmax.

Not that it really matters but I jumped to conclusions because this is posted in the 6.6 Liter 2020 Duramax forum section.

Grumpy Bear · November 26, 2021

15 minutes ago, nutdriver said:

Not that it really matters but I jumped to conclusions because this is posted in the 6.6 Liter 2020 Duramax forum section.

To be honest I didn't even bother to read what forum it was in. The title caught my eye. I just like the topic.

:rollin: