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Grumpy Bears 2015 Silverado 2WD

Grumpy Bear

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On my truck, ethanol from E40 to E85 delivers essentially the same gas mileage.  E0 to E30 delivers about the same mileage as well.


Roger mentioned taking a 30% hit in fuel economy, that is not my experience.  The difference is as little as 18% at highway speeds and as much as 26% in the city.  Overall, it's 21%.


I'll be switching mine back over to E85 soon, but long trips keep coming up and want the range and not have to keep eyeballing Gas Buddy for inexpensive E85 stations along our routes.


The engines love the stuff, even the transmission seems to adapt to it and shifts firmer after a while.

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I have no real world experience using E85, so when I mentioned the roughly 30% hit in mileage I was going by the often published difference in BTU content.  Of course there are many other factors that come into play, one for example could be cD, the lower aero drag vehicles probably would take less a hit, I dunno.  Maybe some one a lot smarter than me can come up with a real world equation (akin to the Drake Equation in the astronomy world) that can come close to the actual mpg loss one would see, not me tho, higher math makes my head hurt.

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10 hours ago, swathdiver said:

Roger mentioned taking a 30% hit in fuel economy, that is not my experience.


11 minutes ago, garagerog said:

Maybe some one a lot smarter than me can come up with a real world equation (akin to the Drake Equation in the astronomy world) that can come close to the actual mpg loss one would see, not me tho, higher math makes my head hurt.


Petty high bar there Roger :) Drake Equation indeed. 🥴


On gasoline the motor is pulling timing on hills, into stiff headwinds and when it is really hot which reduces fuel economy below what would otherwise be optimal. And no running 93 octane did not remove it all. Curious indeed. 


Here is that chart you were referring to. One I constructed from the oxidation of gasoline with various percentages of grain alcohol. 30% when mentioned in writings is a 'round figure' estimate. 


In Peppers case E-50 would result in a 17% loss. Three tank average on E-50 was 26.4 mpg. 


26.4 is 83% of 31.8 mpg. While she has done this in the past during the summer three years ago is was also with 0W20 in her belly during a hot and windless 5 month period. More recently, last summer she hit a high of 29.6 mpg for a 12 tank moving average (10W30). That would be equal to a 10.8% loss. Call it 11% so there is a 6% discrepancy. 


I attribute all of that gain to the octane allowing full advance no matter the ambient conditions. Maybe a small part to a more accurate factory alcohol fuel/timing table??  I expect it can be even better on less viscous oil. Perhaps after the Restore Cleaning is done we can investigate that. 


Not Drake but my best educated guess. 



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One of the nice things with ethanol is that it is cold, which also helps prevent knocking and pinging.  In my old motor, the fuel mixes with the air, reducing the air temperature entering the combustion chamber.  


A good tuner can increase a car's power burning it and make it just as fuel efficient or nearly so.  It's good for a solid 10 horsepower to the rear wheels in the quarter mile in my Gen IV 5.3 engine.  For those of you with 5.3 L83s, it's good for about 25 horses and pushes your torque numbers to over 415 foot pounds.


Both of my Gen IV engines do not experience what Grumpy's chart above shows.  Mine gets better gas mileage with a low mixture of ethanol than straight gasoline and then switches over to the high octane tables when the alcohol content exceeds 31% and is essentially the same all the way up to full strength.



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  • 2 weeks later...

May 2022 Fuel Log


1,118 miles, 40.205 gallons = 27.81 mpg E-10 for 14.08 cents/mile

1,064 miles 41.044 gallons = 25.92 mpg E-50 for 14.13 cents/mile

2,182 miles, 81.249 gallons = 26.86 mpg combine


If current price of $4.68 was applied to the entire 2,182 miles at E-10 mileage the cost per mile would be 16.83 cents/mile.

Blending is saving me then 19%. Or I'm paying effectively $3.79 a gallon. 90 cents a gallon savings. 


Would' a, could' a and should have plus a nickel won't buy a cup of coffee. But boy is it hard to get use to 26 mpg when 28 would be about seasonal average. It's like running winter numbers in the summer for better than summer prices. This only holds up until my supply of CHEAP E-85 vanishes.  

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Pepper is a full blown raging alcoholic. Tired of the E-50 mixed drinks she's dove head long into the E-85 bottle. Locally that is 77% but in my range 70% is more normal. Today paying $2.999/gallon for the 140 proof. I only had room for 8.5 gallons to the tank mix is about 56/56%. More to come. I found five stations between my home a dad's with $3 E85 and my local $3.19 makes this more than doable. 


At 70% I'd take a 24% maximum hit in mileage but as local 87 is a nominal $5/gallon the corn juice is 40% cheaper!!. That puts me 15% to the up side. 


Let me put that in perspective. I'd have to get 37 mpg on E10 to run as cheap at current pricing as I'm running on E-85. 


$3.329 is my break even or 17 mpg.  

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Alcoholic Saves 28% in fuel cost!






I have no idea how it is that the general public gets 17 mpg with the combination Pepper is built upon. I can't get there running 60 into a headwind with the AC on on a diet of 70% alcohol. Not even close. 21 mpg worst. (check the link provided) Fact is I'm not far off the gasoline EPA numbers running ethanol. Curious stuff that. 


In the graph please note that for scaling purposes the alcohol content read from the right hand scale needs to be doubled. 


784 miles 33.758 gallons 23.22 mpg on what amounts to about 70% Ethanol. Compared to the last two year result of 28.04 ethanol has cost, to date, about 20.8% economy loss. This result is about 3% BETTER than the carbon balance would indicated BUT that balance depends on 'all things equal' which they are not. Peppers spark map is in r e t a r d when running something under 40% so my educated guess is the better mapping of the alcohol tables is of 3% benefit. 


This chart shows a steady two point average decline in MPG vs Ethanol content. Three steps considered.  


Lets keep apples to apples and scale this to a 100 mile distance and show the result in cost per mile compared. 


#1 100 miles at 28 mpg at a cost of $5.10 per gallon. (current numbers) 


100 / 28 = 3.571 gallons X $5.10 = $18.21 / 100 miles = 18.21 cents per mile E-10


#2 100 miles at 23 mpg at $3.00 a gallon. 


100 / 4.348 gallons X $3.00 = $13.04 / 100 = 13.04 cents per mile E-70


That's a 28% fuel cost cut! 


$18.21 / 4.348 = $4.19. That that amount per gallon I can pay for E85 at 70% as I break even with current gas pricing. A dollar a gallon is a LOT of latitude. This only gets better as gas prices increase. As I refine my driving on the fuel. As I improve the operating conditions of the machine such as we did in 2019 running light slick oils. And naturally easing up on the miles driven 😉 



Edited by Grumpy Bear
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  • 2 weeks later...

Ethanol Notes: 




Tank fully purged and resting at 75% Ethanol three tanks running. Same source at $3.199 / gallon. I'm running 2 to 3 cents per mile cheaper even with current data suggesting the mpg loss is right on the button BTU wise at 25.7% give or take a tenth or so. It is literally number without out a reliable reference. How so? Can't rerun those miles exactly with the reference fuel now can I? SO what I'm using is the closest historical summer average in a year with a similar tune and kids that is as good as it's going to get. 


I now have 2,750 miles on this OCI and every mile on Ethanol of 46% or greater. Ever smell your oil on gasoline? Even if dilution is really low the smell is burnt like. Fresh oil smells...well...like fresh oil. Ethanol oil really hasn't much of a odor at all. Nor as I'm learning does it color like gasoline fueled motors. Not much change at all. At least on the dipstick. Curious stuff that. 😉 


Almost forgot. I put up the KR and TIR and pinned her ears back. Yea. No r e t a r d until right at the top of the gear during the change and then only a 2 degree pull. Not the way this works on gasoline. KR pulls back hard enough dampen acceleration. Not on Ethanol.  And this little six will bark the tires hard on a rolling tip in from 30 mph to near the top of second gear. Wonder what happens if I tap off the traction control?

Edited by Grumpy Bear
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  • 3 weeks later...
8 hours ago, Doublebase said:

How many miles on Pepper nowadays? Last I checked you were heading to 150,000? 

Plan on keeping Pepper to 300,000? I love high mileage stories, especially well documented ones. Hope all is well.

Hi Mike. Where ya been? 😉 


159,008 as of this very moment. Just went out and checked just for you. :) 


300K? I'd like to say 3 million but I doubt I will live that long and GM just fights me to much. Sometime this week I have to make an appointment for those "Killa" air bags. Told me about a year ago, maybe longer, the inflation cylinder may fail and KILL ME so park it until we get around to ya. :crackup:Nice to see GM has my best interest held close to their little black hearts. They just sent me the 'were ready' order this weekend. 


Other that that....she's running like a Swiss Watch. I have to admit I've been neglecting her of late. Putting all my time into Sugar Bears Terrain. That thing has become a non paying full time job. 


Recalls account for 99% of all the work Pepper has needed non routine. Between these two we've logged more recalls and TSB's that in all my other cars combine. That's over 50 years of cars. Thing is Mike....were would I go? :( 


So I make Pepper and Dizzy last as long as possible then do the down hill run with the Buicks sitting in storage. 



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  • 3 weeks later...

7/28/2022 Service Notes:


159,280 miles


Pirellis took another puncture. Two this time in the same tire as last time. A screw and what looked like a hypodermic needle. Patched and back on the road. While dismounting them we noticed a good amount of cracking between the treads. These tires, by date, are 3 years old. That is disappointing. 35K on them. 6.5-7/32 still left and very even wear. Yea, I'll keep running them. Squirrels are in no danger. Neither are they from reaching the Bridgestone 125K service life. 


Has taken a pint of makeup oil since the RESTORE was charged 4,250 miles ago and alcohol became the fuel. Curios that is, eh? Does GM have this drop over dead at 150K nailed or what? 🤣 I suppose it's about time to give her a tune up. 



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