Octane Rating

[c3po]

My 2004 Mercury Marauder calls for 91 Octane Gasoline, in my area we only have: 87, 89, and 93.

I have been using 89 for the last 2 years except when I go on a long trip I will put in 93

Last week I put in 93 Octane Gas and I really did not notice a difference since I do not drive the car hard.

I really do not want to fill the tank halfway with 89 and then 93 which would make a 89 octane rating.

Do I just stick with the 89 octane rating or do I need to keep using the 93, if you use a higher octane rating then recommended can this cause problems just like using a gasoline with a lower octane reading than specified lead to problems.

 

[Billbert]

If it does not ping on 89 and you see no reduction in gas mileage, run the 89.

 

[JHZR2]

So long as it has a knock sensor, it should be no worries... You will retard ignition, and thus have less efficient combustion and lower power, but there should be no damage.

The AKI of your fuel is just the numerical average of the gasolines added, over the gallons of each. Mixing some 93 with 89 is a great way to get near your 91 without going over.

One thing Ive wondered about is what happens if the computer is always adjusting because of changing AKIs for the gasolines used. Does the computer get confused? Is it less efficient as it is hunting and changing timing vs. just set in one map.

 

[HTSS_TR]

I had been using 87 Octane in '94 LS400 some years now without any negative effect in normal city/highway driving, the gas mileage is about the same as with recommended 91. The only time I can feel the car needs 91 Octane was going to Vegas in summer, the car felt sluggish climbing the steep hills near Death Valley with ambient temperature above 120F.

Higher octane, 93 vs 91, does not cause problem but it does not have any positive effect either. Half 89 and half 93 to get 91 save you some dough, or just run 89 if you don't notice any different between 89 and 93.

 

[tomcat27]

certainly if you were running a turbo or supercharger, I would run 93. In your case, run 89 all of the time and dont worry. as others have indicated, the car will adjust to the lower octane. as far as running 93 on a trip - not really needed. when you really need the octane is when the engine is run under an above-average load (such as towing).

now, for people that run 93 in a car that calls for 87, they are wasting their money and potentially losing MPG.

BTW, with the exception of BP's Ultimate, did you know that in most areas of the county most brands of gas are sourced at the same gas depot, and only a very small amount of additive will actually be different?

 

[CivicFan]

I fill up when the tank is half empty and alternate between 89 and 93 every fillup. So the gas in the tank is close to 91 at all times.

 

[lexus114]

Originally Posted By: c3po
My 2004 Mercury Marauder calls for 91 Octane Gasoline, in my area we only have: 87, 89, and 93.

I have been using 89 for the last 2 years except when I go on a long trip I will put in 93

Last week I put in 93 Octane Gas and I really did not notice a difference since I do not drive the car hard.

I really do not want to fill the tank halfway with 89 and then 93 which would make a 89 octane rating.

Do I just stick with the 89 octane rating or do I need to keep using the 93, if you use a higher octane rating then recommended can this cause problems just like using a gasoline with a lower octane reading than specified lead to problems.


You have to fill up at least twice to really notice the difference.

 

[panthermike]

I used to run 89 in my 94' Mark VIII, same engine as your Marauder. It did fine and didn't ping. As others have said, as long as it's not pinging it should be fine. I would definately run a fuel treatment once a year anyways, at least that's what I did on the 94'.

 

[c3po]

Originally Posted By: panthermike
I used to run 89 in my 94' Mark VIII, same engine as your Marauder. It did fine and didn't ping. As others have said, as long as it's not pinging it should be fine. I would definately run a fuel treatment once a year anyways, at least that's what I did on the 94'.


The only thing that has me questioning about maybe putting in 87 Octane is that this is a 10 to 1 Compression motor.

I am running a bottle of Redline SI once a year and in every tank I am using a Maintenance Dose of MMO

I filled up the tank today with 89 octane gas and I did notice that with the last run of the 93 octane that the insides of my tailpipes were a little bit darker than before, this may not mean much since the winter gas could be causing this now.

 

[JHZR2]

adds MAY lower octane rating (AKI) actually. So beware of that too...