Octane and DTE

Epillon · Jun 24, 2016

I'm an ultimate creature of habit so I always fill my truck when it gets to half a tank. I go to the same Chevron at literally the same pump so long as it's not taken (yes, I'm OCD). I typically use their 91 octane, about 15+ gallons which always puts me around 415-425 DTE at my consistent 13.5 mpg.

Soooo, I filled my half tank today but I used their 89 octane and noticed my DTE was only 390. I couldn't find any satisfactory answers yet so just wondering if anyone else experience this phenomenon?

Just seems weird I lost 20+ DTE and the only thing different I did is use a lower octane gas. My pea brain hurts, please help.

7777xm · Jun 24, 2016

The distance to empty seems to be calculated on current and the last tanks driving habits. Just putting a different octane in isn't going to affect how the truck determines distance to empty.

It will also fluctuate depending on how the pumps Auto shut-off works. If the pump turned off a little prematurely and you did not get the exact same amount of fuel, your distance to empty will be lower too.

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Hootbro · Jun 24, 2016

^^^^^^^^^^^^

What he said. Your truck does not know what you put in until it gets into the fuel cycle and is used.

The DTE and the "Lie-o-meter" MPG results has too many variables to be accurately relied upon.

xrsman · Jun 24, 2016

What these guys said ^

You probably won't notice much of a difference, if any in mpg between the two octanes.

GP4L · Jun 25, 2016

Hootbro said:
^^^^^^^^^^^^

What he said. Your truck does not know what you put in until it gets into the fuel cycle and is used.

The DTE and the "Lie-o-meter" MPG results has too many variables to be accurately relied upon.

Not always true. My "Lie-o-meter" have never been more than 0.3mpg off, high or low, and is usually almost dead on with my calculator. But I reset mine immediately after starting the engine after topping my tank off. I'm willing to bet that I'm in the minority of people having an accurate EVIC, as well as resetting it after every fill up.

TRCM · Jun 25, 2016

GP4L said:
Not always true. My "Lie-o-meter" have never been more than 0.3mpg off, high or low, and is usually almost dead on with my calculator. But I reset mine immediately after starting the engine after topping my tank off. I'm willing to bet that I'm in the minority of people having an accurate EVIC, as well as resetting it after every fill up.

I always reset mine before I even start the truck after filling

and my MPG computer has always been off by 1.3 mpg or more in this truck

Now the silverado I traded in, it was always within .2 mpg, no matter what or how I drove it

BlkZrx · Jun 25, 2016

I just ran thru a full tank today, mixed 70 and 55 highway, 464 miles.
Averaged 18.6 on EVIC , hand calculation was 15.4. Last time I checked it was off about 1.5 mpg.

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jasonw · Jun 25, 2016

My liar-display is spot on roughly 5% of the time. The next 45%, it is within 1 MPG of the calculator. Another 40% or so, its within 2 MPG. The remaining 10% of the time, its off by 3 MPG. I don't recall it ever being off by more than 3-4.

noupf · Jun 25, 2016

a couple things.....

1) You are literally wasting your money when you purchase the 91 octane. Unless you have a tune, it does literally nothing for you or your motor. Any octane over whats recommended ( in this case 89 octane ) is 100% unnecessary ( not my opinion, its a fact ). Running less than recommended can be a problem, running more is a waste of money.

2) As others said, your evic will have no idea what octane you put in, so the 91 or 89 has zero affect on how it calculates distance till empty. The odds are, your average mpg ticked down ( heavy foot for a couple days, more start and stop driving than normal and so on ) and when you filled up, the calculation was less than what you are used to seeing.

3) go back to #1 and start saving yourself some money.

Epillon · Jun 26, 2016

Out of curiosity, anyone else have Rebel Stations or whomever that offer 'Racing Fuel' at the pump? Most, not all, Rebel Stations have a '100 Octane Race Fuel' for $6+/gallon. I've never used/tried this because Lord knows what that actually is and what it'd do to my motor.

Anyone ever try it? I'd assume if your not tuned for that high an octane it's not a good idea but what actually happens?

sriley531 · Jun 26, 2016

There's a station near me that sells turbo blue out of a pump. I've run it in atv's and my Buick, but there's no way I'd run it in my truck. At $7 a gallon there's be nothing to gain in our trucks (other than a nice smell). You'd literally gain nothing. If you've got some juiced up compression/boost/etc then it may be warranted, but otherwise pointless.

cgeorgemo · Jun 26, 2016

Epillon said:
Out of curiosity, anyone else have Rebel Stations or whomever that offer 'Racing Fuel' at the pump? Most, not all, Rebel Stations have a '100 Octane Race Fuel' for $6+/gallon. I've never used/tried this because Lord knows what that actually is and what it'd do to my motor.

Anyone ever try it? I'd assume if your not tuned for that high an octane it's not a good idea but what actually happens?

It's gasoline with 100 octane rating. It will help people with extremely high compression motors avoid premature detonation (knock). Since our trucks aren't that high a compression motor it will simply cost you more money at the pump. There would be no harm to your motor but also no benefit.

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Mbrp.Ram · Jun 26, 2016

Not exactly

With the higher octane, the combustion is stronger, which in turn will cause more strain to the components intended for midgrade ideally. A few tanks sure go for it see what it'll do, prolonged use not recommended.

Good regards,

Mbrp.Ram the engineer

Epillon · Jun 27, 2016

So just for clarification, there's absolutely no benefit in running 100 Octane but unless I use it often it won't harm my motor. I'd like to add just 2-3 gallons so I can get that "trick gas" smell when I pass people. Lol.

cgeorgemo · Jun 28, 2016

Mbrp.Ram said:
With the higher octane, the combustion is stronger, which in turn will cause more strain to the components intended for midgrade ideally. A few tanks sure go for it see what it'll do, prolonged use not recommended.

Good regards,

Mbrp.Ram the engineer

This isn't correct.
Higher octane is needed in a higher compression motor but it isn't the reason for the increase in compression it is the additive that makes the engine not detonate early in the compression cycle.
Unless your engine is pinging there is no need to buy higher octane gas than recommended but doing so will not harm your motor just your pocketbook.

noupf · Jun 29, 2016

Mbrp.Ram said:
With the higher octane, the combustion is stronger, which in turn will cause more strain to the components intended for midgrade ideally. A few tanks sure go for it see what it'll do, prolonged use not recommended.

Good regards,

Mbrp.Ram the engineer

yea, this is not correct in the slightest. The combustion is not stronger and there is absolutely no extra strain on the engine components. In fact, its really the complete oposite, sort of....... Running LOWER than recommended octane is what can harm a motor and its internal components, its called knocking or pinging. Any octane over what is needed ( recommened ), based on the the compression ratio of of your motor, is a 100% waste, literally.

To the OP, just run 89 octane and stop over thinking it. Don't run 91 or higher, its a wast of money. There is literally nothing to gain from running anything over 89 octane. At the same time, dont run 87 ( even though many do ), it has the potential to harm your motor. Ram recommends 89 for a reason. trust them, they arent lying to you.

cgeorgemo · Jun 29, 2016

noupf said:
To the OP, just run 89 octane and stop over thinking it. Don't run 91 or higher, its a wast of money.

Unless you add a tuner that changes your engine's timing, then you'd want to run the octane the tune recommends.

U&A · Jun 29, 2016

does anyone know how long it takes our truck to adjust timing when you switch octanes?

I originally ran 93 in my truck and it was suggested to see if i can get better mileage with 89. so this tank has been 89 and there really is no noticeable difference after 3/4 tank used up.

Hootbro · Jun 29, 2016

U&A said:
does anyone know how long it takes our truck to adjust timing when you switch octanes?

I originally ran 93 in my truck and it was suggested to see if i can get better mileage with 89. so this tank has been 89 and there really is no noticeable difference after 3/4 tank used up.

It is going to adjust the Nano second it detect any pre-detonation in the fuel. I doubt most would notice the change until they are in the power band under load and not normal daily driving.

U&A · Jun 29, 2016

Hootbro said:
It is going to adjust the Nano second it detect any pre-detonation in the fuel. I doubt most would notice the change until they are in the power band under load and not normal daily driving.

I was talking about noticing a difference in MPG. i know you'd never notice the power diff.

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