Its not about the octane rating with the ethanol, its about the energy produced from the ethanol.
Ethanol reduces MPG, that is a fact, look it up.
BUT ethanol burns cleaner than gasoline, so they add 10% to the gas to make it pollute less, but you loose MPG when you use ethanol mixed gasoline so you use more of it, makes no sense to me, but I didnt write the law, which was written and put in place in the '80's.
Again, its not about the octane rating, 100 octane with a E-10 mix is still 100 octane.
Octane is about the rate of the burn, these engines are tuned to run on premium, bottom line, end of story.
Higher octane gas burns slower.

That being said, if you can get 89 octane ethanol free, go for it, your MPG will increase, because there is no ethanol to reduce your MPG.

 

Everyone's answer will be different. I run the highest I can get because I have seen first hand how carbon builds up with cars using low octane gas. Not fun pulling a V12 apart because the owner didnt want to buy premium gas.

 

I always use premium in mine. I'm with spike about the ethanol thing. I have a buddy that runs a built Ford 302 in his Pinto (yes, Pinto), and he has troubles with running it on pump gas around here. High octane without ethanol (there's one station in town that has it), it runs great. High octane with ethanol, runs like crap. I had similar problems with a truck I built.

 

Rover engines for years have had valve/carbon issues when running cheap gas. To my way of looking at it, it is cheaper to run good gas, get more torque and MPG then it is to do a valve job.

 

Well, that settles the issue, responses all over the map, from one extreme to the other---LOL. I gather that this issue is filled with a lot of emotion, you think ----LOL? Someone asked if I have been using regular gas. On my 1991 Range Rover classic, 3.9 Litre, engine rebuilt by me, engine tuned for lower octane fuel; now with many miles on rebuild, without a problem, I have been using regular unleaded gas every day, with no burnt valves or any other problems, though I intend, soon, to buy a 2004 Discovery, 4.6 engine. The 4.6 engine is, as you all know, managed electronically, unlike my 91 3.9 engine. However, if desired enough, I think that it could be electronically tuned for lower octane fuel too. One thing I think I now know about this whole issue, is that it is filled with a lot of emotion from Rover owners! Thanks again for input.

 

If low octane regular is used - the engine will ping.
The knock sensors will detect the ping and retard the timing.

but, the ping alone is going to destroy the head gasket crowns eventually from heat.
Then the flame gets out and blows thru the head gasket.

Sure, you like changing head gaskets - put in your regular.
Fill it up.

The knock sensor argument is like - well, yeah, I wear my seat belt.
Good for you.
You get into an accident and you don't fly out the window - but you still face harm and damage.
The knock sensor can only do so much.

 

Like I said before, why bother taking the chance for a $5 difference in price per fill up.

Either way you do need to use top tier gas with detergent and use a good fuel system cleaner (Techron, Seafoam, etc) every 3000 miles or so.

If you are thinking of saving another two are three dollars per fill up by buying discount brand or grocery store grade regular fuel with ethanol you will be paying later.

Not worth it.

 

E-85 is 105 octane, even cars designed to be ran on E-85 get less MPG while running it.

I just thought of this today, I am the 2nd owner of my truck, the original owner used premium gas, I use premium gas 98% of the time, my head gaskets are original.

 

Yesterday I asked previous owner what gas he used. He claims he used regular unleaded with no problems. I wish I had taken pictures of the dirty throttle body I cleaned while replacing the heater plate and all related hoses. He also didn't use coolant and truck was virtually bone dry when I picked it up.
Needless to say, after spending approx. $1,000 on deferred maintenance, I will only be running premium unleaded. My vehicles typically last me well over 200,000 miles and with proper care I expect this one will as well.

 

He had no problems as you bought the truck.
You may have problems from later from how the previous owner treated the truck to regular gas in the past.