I have a 2010 F-150 STX. It has a 4.6L V8. Everything is stock. I have been putting 91 octane in it since i got it (a year ago). Is this really that necessary? What octane fuel do you put in your truck? What are your thoughts on paying the extra $3-$5 to fill up?

 

Who told you to use 91 man? Any stock F150 uses 87 and Anything higher is a waist of money and does nothing unless you have a 91 Octane tune then you have to use 91 or 93 do to the more aggressive changes in setting for the PCM.

I have a 08 STX with 4.6L and i use 87 unless i go level 3 91 tune with my Edge Evo.

 

See I didn't know. I don't have any tunes, everything is stock. I am trying to increase my MPG, but can only seem to find places est. 1-2MPG increase. It dosnt seem like enough to spend the kind of money to get that. I'll go to using 87 then.

 

Sometimes the higher grades of gas are 100% gas with no ethanol. That could be why you'd get better mpg's. I use 89 octane because it is 100% gas,(in my area) and only 10 cents more per gallon, and now get close to 19mpg's on the highway.

 

Don't waste you money Tim. I've owned four 4.6L's, and they do just fine with 87 octane. Even in the Wifey's previous 2010 Mustang GT, when I filled it with 91 I couldn't tell any difference in the performance. The only difference was a lighter wallet.

 

Unless you have a tune that requires higher than 87 you wasting your money.

And FYI there isn't a middle grade fuel made, it's actually blended at the pump between the lower and higher grade.

Wayne

 

It's a wash in the end when ya do the math really. Some higher octanes, if 100% gas, will give better performance and MPG's, but if the 91 you're using is a 10% ethanol blend, you're likely wasting money. If you sit down and really crunch the numbers, you might be coming out a couple dollars ahead in the long run using the higher octanes. Not sure it justifies itself though. With peoples' budgets in the wringer, most everyone is buying the cheaper fuels to save a buck. This means that the 87's are almost always the freshest fuels available. To me fresh fuel out-weighs the other so-called benefits. Run the 87 and save your money....unless of course you find a performance difference that you prefer over the cost difference.

 

I did a quick Calc a few months ago. I only put in premium, and usually pay about 10-20% more. I have observed an MPG increase of 1-3 which comes out to 5-15% increase.

So no, cost is not justified by MPG alone. I do though feel that premium is better for the engine, but that is another debate. Plus now I'm running a 93 tune so premium regardless.

 

Don't mean to highjack the thread, but I'm glad the OP asked this question as I live in TX and had always run 87 octane until I went to work in eastern Colorado and western Nebraska where 85 octane is in the base unleaded with ethanol. To get the 87 octane w/o ethanol you pay 10 cents more. My truck is new and has the 5.0 with less than 5k miles. I have not had any problems with performance or heard any pinging. The elevation is between 3,500 and 5,000 ft. Is that why they offer the lower octane level in this region?