85 or 88

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Except it isnt. Using a lower octane in a higher compression engine will result in knocking and eventually failure.

Now for same octane rating, there is not much difference. Gallon for gallon, ethanol free delivers 100 units, while E10 delivers 96.6 units of energy.

How much of a premium are you willing to pay for 3.4 units of energy? It is easy to do the math to see if it is a bargain, but most ethanol free pumps are overcharging significantly for that extra 3.4.
As always, “better” is in the eyes of the beholder. I agree that ethanol free isn’t generally economically better based on price per gallon or per mile. I’ve measured my fuel economy and ethanol free gives me 1.5 to 2 mpg better. With my aux tank, I have 48 total gallons which means about 70 to 90 miles more range. That’s my “better”. Pricewise in KC, it’s generally a wash or if you have to buy premium to get ethanol free, less economic.

85 octane isn’t generally a choice except in places like Colorado and Utah. I would not choose to run 85 in my 200 but have when I had no other option. I didn’t notice any knocking or issues with it. Running 85 long term probably isn’t great for a 200.

I don’t think 87 vs. 91 makes any real difference in a 200. Others will disagree and that’s fine. I could be wrong. I just do not hear any difference, see any mpg difference, or feel any power difference. I do fill up with premium if I’m going to not drive for a few months over the winter because I believe the additives are better but I have no science to back that up.
 
This. And the ethanol has a higher heat of vaporization and so it will cool the air charge and cylinder more than non-ethanol fuel and I dont believe that is captured in the octane rating.
Interesting. I’m not going to say I understand this or that what I’m about to say is even related but in my experience, 200s running ethanol free gas seem to experience less boiling gas’s issues at elevation/high ambient conditions. Personally, I’ve only boiled a couple times while in Colorado (I live at 925’) but each time I hat 87 10% ethanol gas in the tank.
 
I run whatever is cheapest. Always have. Matters zero to a 200 (or a 100, 60, or anything else).
Nothing but the "Finest Cheapest" fuel here either. She'll run just fine on whatever you can find.
 
Nothing but the "Finest Cheapest" fuel here either. She'll run just fine on whatever you can find.
Part of the reason I have been driving Land Cruisers for almost 40 years. When I am back of beyond and need fuel the vehicle needs to run on whatever I find. Can’t tell you how many times I have run unknown octane unleaded that was so dirty I had to use 3-4 stacked coffee filters to filter it. Whatever it takes.
 
Yeah I pretty much run exclusively 85 (with ethanol--don't know exactly how much), but I'm at ~6,300ft in CO. Common fuel to see around CO.
 
My local Sinclair here in UT.
IMG_7643.jpeg
 
My local Sinclair here in UT.
View attachment 3901939
BTW, my LX did not like the 88 ethanol free. My KCLV normally runs around 17-18 with 91 and it tanked to like 10-11 on the Sinclair 88. I’ve never seen it that low.

I used this tank in pretty much 170 miles towing getting an atrocious 8 mpg
 
Except it isnt. Using a lower octane in a higher compression engine will result in knocking and eventually failure.

Now for same octane rating, there is not much difference. Gallon for gallon, ethanol free delivers 100 units, while E10 delivers 96.6 units of energy.

How much of a premium are you willing to pay for 3.4 units of energy? It is easy to do the math to see if it is a bargain, but most ethanol free pumps are overcharging significantly for that extra 3.4.

Agreed.

To add, octane, ethanal, vapor cooling, vapor pressure (RVP), energy content, additives and cleaners, blah blah, are all discrete factors of fuel that is all too often conflated. Each factor effects things in a different way.

BTW, my LX did not like the 88 ethanol free. My KCLV normally runs around 17-18 with 91 and it tanked to like 10-11 on the Sinclair 88. I’ve never seen it that low.

I used this tank in pretty much 170 miles towing getting an atrocious 8 mpg

To @Umbrarian and your point, octane matters particularly to LXs that are tuned for the higher test stuff. Especially in high load operation like towing and long grades, and I likewise see KCLVs and performance fall off a cliff.

Yes, with altitude and less atmospheric pressure, there is lower peak cylinder pressures which requires less octane. What sucks is leaving the local area and returning to lower elevations in summer, and having to deal with low octane performance when towing. Just went through Death Valley Stovepipe Wells which is 10 ft above sea level on a 105 degree day, and they only had 87 octane :mad: . Good thing I was dropping off the trailer for a backcountry leg, as otherwise, that would be knock city. Made sure I got high test before returning to pick up the trailer.
 
Agreed.

To add, octane, ethanal, vapor cooling, vapor pressure (RVP), energy content, additives and cleaners, blah blah, are all discrete factors of fuel that is all too often conflated. Each factor effects things in a different way.



To @Umbrarian and your point, octane matters particularly to LXs that are tuned for the higher test stuff. Especially in high load operation like towing and long grades, and I likewise see KCLVs and performance fall off a cliff.

Yes, with altitude and less atmospheric pressure, there is lower peak cylinder pressures which requires less octane. What sucks is leaving the local area and returning to lower elevations in summer, and having to deal with low octane performance when towing. Just went through Death Valley Stovepipe Wells which is 10 ft above sea level on a 105 degree day, and they only had 87 octane :mad: . Good thing I was dropping off the trailer for a backcountry leg, as otherwise, that would be knock city. Made sure I got high test before returning to pick up the trailer.
I had extremely good luck with Boostane in my F150. I used to bump my 91 to 94 or, once, 96 octane and that thing used every bit of it.

Might be worth carrying a bottle for situations like that.

I’m sure these engines are not able to maintain MBT spark anything besides low load. Even at elevation, I’m sure they are running well below MBT.
 
I had extremely good luck with Boostane in my F150. I used to bump my 91 to 94 or, once, 96 octane and that thing used every bit of it.

Might be worth carrying a bottle for situations like that.

I’m sure these engines are not able to maintain MBT spark anything besides low load. Even at elevation, I’m sure they are running well below MBT.

Not a bad idea. I have some VP octane booster for my other car on the shelf and never thought to carry it.
 
I recently had a conversation with a friend that made me wonder if I could get better MPG (or performance) by using a higher octane. I have never put anything in my Land Cruisers other than 85 which is the standard base around Utah. I started running 87 which is the middle grade around here. I've now done this for several tanks and somehow forgot about my MPG quest. I found it odd that my dash has recently been reporting back higher MGP numbers. Only after did I remember I was doing an experiment with the higher octane.

I then asked ChatGPT:

To determine how much your fuel mileage (MPG) would need to increase for it to be financially worth switching from 85 to 87 octane, we can run a quick cost-benefit comparison.

Step-by-step Calculation

Let’s assume the following:
  • Price of 85 octane: $3.40/gallon
  • Price of 87 octane: $3.60/gallon
  • Baseline MPG on 85 octane: 13 MPG (typical for a 200 Series Land Cruiser)
We want to know what MPG you’d need on 87 octane to break even.

Fuel cost per mile (CPM)

With 85 octane:

\text{CPM}_{85} = \frac{3.40}{13} \approx 26.15 \text{ cents/mile}

With 87 octane:

Let’s call the unknown improved MPG “X”

\text{CPM}_{87} = \frac{3.60}{X}

Set CPMs equal to find break-even:

\frac{3.60}{X} = \frac{3.40}{13}

Solve for X:

X = \frac{3.60 \times 13}{3.40} \approx 13.76 \text{ MPG}

Conclusion


You would need to improve from 13 MPG to about 13.76 MPG (a 5.8% increase) for the switch from 85 to 87 octane to break even financially, given a 20¢ price difference per gallon.

If your vehicle doesn’t gain at least that much efficiency — and many don’t from such a small octane bump — it’s not worth it from a cost perspective. However, factors like engine longevity, reduced knock, and performance under load might still make it a worthwhile choice.
 

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