Gas Mileage

Some of the higher octane fuel in my neck of the woods is fortified with ethanol to boost the octane. In the grand scheme of things it will probably reduce the mpg.
B.O.

I tested a higher octane once, and I got higher MPG, but the effective cost per mile was about the same. However, the FTC says that's not true, so maybe I was mislead by the MPG numbers I was seeing on my car's computer. Anyway, I buy regular gas since that's what my owner's manual says.

Here's the FTC link:

FTC Report On Premium Gasoline

The L96 6.0 in my 2015 Chevy 2500HD, I find that using E85 I get much better overall experience with hauling, towing, etc. Fuel mileage does indeed tank considerably by using E85, but compared to mid grade and especially premium fuel cost, the actual cost per mile by using E85 is still far less than using those other fuels, and equitable compared to regular.

GM engines, the ECM monitors knock events and adjusts timing accordingly. E85 has 100 octane and allows the ECM to advance timing to max in the ECM map. Driving experience is much better. I could get the same result using premium, but the actual cost per mile would be higher.

As has been stated, higher octane will not deliver better mpg, but it can under some circumstances bring about better overall performance efficiency.

A pickup with a trailer is an aerodynamic nightmare that is going to be a real belly drop when it comes to mpg. A more moderate speed, gradual slowing instead racing full bore and then applying a ton of braking, and other little techniques will go a lot further to improving mpg. Many commercial fleet studies show that the driver alone accounts for 33% of improvement or degradation of fuel economy.

dodge guy wrote:

Lynnmor wrote:

azdryheat wrote:
Octane has nothing to do with mileage.

It sure does if the knock sensor detects knock and the ignition timing is adjusted to compensate.

Yes it does. I proved it on my V-10 Excursion. Used to run 87 and power and mileage were down horribly! Switched to 93 and it improved. The. I got a tune from 5 star for 89 octane and it was better. My truck was over maintained so it was running 100%. You may not see a lot more mileage but you should feel the performance.

OP. Only you can decide. Run 2 tanks while towing and see for yourself.

Actually you are all correct

If when new, your vehicle manufacturer states that regular gas is all that is required then you will not get any benefit from running premium gas. Your engine is already running as efficient as it can.

If your engine is very high mileage and has substantial carbon build up in the combustion chamber, it may slightly increase compression to the point of pinging under load. In that case you would get a benefit from premium fuel. The higher octane will only assure a more efficient fuel burn, preventing the pre ignition ping as some call it. When the knock sensor detects poor fuel burn/pinging the computer will adjust the timing in an effort to reduce the harmful detonation. This will reduce performance and mileage. So in this case yes it will help you get back to where it used to be before the carbon build up happened. But still no gain from when the engine had no carbon build up.

The only thing that will improve power is compression. Performance engines manufactured with higher compression pistons or crank strokes will require a higher octane fuel. Those cars will recommend to only use premium fuel.

So, too low of octane can cause detonation and reduce power and mileage, but once the balance of octane is achieved to eliminate preignition, it has reached it's ultimate goal. There's nothing left for it to do.

Speed and wind resistance will make the biggest difference in mileage.

Only way to improve the mpg on that truck would be to install the Duramax kit. :)

Lynnmor wrote:

azdryheat wrote:
Octane has nothing to do with mileage.

It sure does if the knock sensor detects knock and the ignition timing is adjusted to compensate.

Yes it does. I proved it on my V-10 Excursion. Used to run 87 and power and mileage were down horribly! Switched to 93 and it improved. The. I got a tune from 5 star for 89 octane and it was better. My truck was over maintained so it was running 100%. You may not see a lot more mileage but you should feel the performance.

OP. Only you can decide. Run 2 tanks while towing and see for yourself.

azdryheat wrote:
Octane has nothing to do with mileage.

It sure does if the knock sensor detects knock and the ignition timing is adjusted to compensate.

If it did improve your mileage a tiny bit, it would still never offset the higher cost of the premium fuel.

Octane has nothing to do with mileage.