I left my buddy at the pump while I ran in to grab some brews and when I came out, he had already pumped about 12 gallons of 89 octane gas by mistake. I had about a 1/4 tank of premium in there already and was able to pump about 2 gallons of fresh premium but that's all I could get it. Will burning this gas off cause any damage or should I have it drained?

 

just drive it slow and don't WOT it, the ECU will retard the timing accordingly to prevent pre-detonation.

 

See if you can pump out that gas or drain it from the bottom of the gas tank.

 

this, drive like a grandma until the gas is almost empty.

 

dont worry nothing is going to get damaged.

 

 

but if you're worried, you can always siphon it out.

 

Burn off a few gallons driving to a station that sells 100 octane. Even adding two gallons will have you back over 91 octane, but I wouldn't sweat it regardless.

 

just dnt push it...will b fine

 

it will explode.

 

What car are we talking about here? Isn't the OP still waiting for his C63?

 

Slightly Off Topic - Excuse me but isn't 93min required for the C63 guys?

OP don't worry about the low octane, if you have been running on 91, its still less than what is required anyway, just don't make the mistake of putting low octane again.

 

Put a bottle of octane boost in the tank. Call it done!

 

...

 

93 in Houston.

 

Absolutely nothing will happen. This would not affect the engine if not repeated. Higher octane number will reduce residues and build-up and all the debris from lower octane, and powers higher performance engines. You mixed it, it will be fine. Do not do it again...

 

I concur with this.

 

Forget about it, your ecu will adjust.
The high octane gas is used by the manufacturers to get better fleet mpg's and higher performance numbers.

You might (or might not) notice slightly lower performance and maybe 5 to 10% lower mileage but otherwise, it's a wash.

 

my nissan reccomends 91 or better and for the past 5 years and 100k miles i have ONLY ran 87 octane. no issues. its not a super high performance engine and i do use 91 in the C but you are going to be fine. just drive it normal and fill it about half way empty with 91 and forget about it.

 

On the gas flap it says recommended 93 but with certain states we can only put 91 octane unless we want to drive out of our way for 93 or higher

 

I guess the only way to keep the Octane level high enough would be Octane Boosters. I am still learning about my C63 and just like any car, lower octane would mean engine problems in the long run. Knowing that 91 is more common in the U.S., Amg should have modified it for the U.S. market.

 

Dont worry about it at all. Drive the car as you normally would. All these people saying drain it are idiots.

 

Beware of octane boosters. The ones that are reputed to work generally contain an ingredient called MMT that leaves combustion chamber deposits. I used to buy an MMT octane booster wholesale in case lots from a friend but then I saw the deposits firsthand in my M3's engine when the head was taken off for valve work...odd beige-pink colored deposits...that was the last time I have ever used an octane booster.

 

87 US Octane (91 RON) rating can also be used but you'll just have a bit less power available.

 

Well the key word is RECOMMENDED and not "Required" but in any case 2 octane is not going to make a huge difference. If my knowledge is correct in general the ppl who use 91 octane will just be a tad slower because with the higher rating it just means the fuel is easier to burn. Correct me if I'm wrong though. BTW I personally wouldn't recommend putting octane boosters in the car as the person above says it will leave deposits.