Im using unleaded 87 octane on my car and I'm hearing some knock and pinging when I go over 50. The manual says to use regular. Should I change to Premium or will this damage the engine? I've heard that once you use premium you cant go back to regular.

 

Ive only used 89 since I got my mustang. Even though the manual says 87 is fine

 

Why the heck would premium damage the engine?

 

I was under the impression that with newer cars, including the mustang, it was not a good idea to use higher than recommended octane gas. Since the timing is set up for 87, I believe not only will using higher not help, but will actually hinder performance. This of course is assuming you have not flashed the computer to advance the timing to use higher octane gas.

 

Never heard of higher Octane being bad. Maybe overkill, but not bad.

 

Well the new mustang is tuned for 87. If you run the higher octane you are wasting your money unless you have reflashed with a new tune for the higher octane. Yes you can actually run worse with higher octane without a new tune. Probably wont notice it, but there could be detonation, etc. It is tuned for the 87, so I suggest using it. If you have a ping knocking sound with regular gas, I would take it to the dealer immediately. There are some known tsb issues in regards to coils/ computer reflash for some things, dont put higher octane gas to try and fix a problem with the car. If pinging and knocking is present over 50 you have a problem. Go to dealer, it maybe as simple as the newest computer eeprom flash. good luck

 

If your hearing pinging/knocking now....go to your dealer....

 

So, it is actually true that once you go to 93, you can't go back to 87. I have a 93 tune, but am thinking about changing it to my 87 tune again to save $15 a month in gas. Is this ok?

And one more thing since we are on the subject of gas grades... is it also true that you get worse MPG using 93 gas than you do 87? Does 93 burn faster?

Thanks in advance.