Got caught on just about empty and wasn't near my discount gas station, so I took a shot and put in 2 gallons of regular. I reset the trip indicator to see how the car did with regular. The next day I filled the car with 93 octane and reset the trip indicator. Not only did the car feel as though it was performing better (purely subjective,) but the mpg increased by about 3-4 mpg (purely objective.)

 

Interesting to know.
Ive debated about putting the 91 O fuel in , but I fear anything less than whats called for (92) could jeopardize the engines long term performance?

I wonder how true that could be ... but then again with a car like this im not sure its worth chancing it.

 

Page 346 of the 2017 C300 Coupe owners manual states you shouldn't use less than 88 octane AKI. But in an emergency it's probably fine if 91 or better is not available. In order to compensate for the lower octane the engine management will have to pull timing to prevent detonation aka knocking/pinging. As a result you'll experience a great reduction in HP and probably a decrease in MPG as a result of the engine not igniting the fuel at the optimal time it was designed for.

I'd be interested to hear your results comparing 91 AKI and 93 AKI... Theoretically there shouldn't be any difference but I'd be interested to see if there were.

Page 345 of the 2017 C300 Coupe owners manual states that the recommend octane for refueling has an octane rating of at least 91 AKI and it shouldn't hurt long term performance. I know because we live on the West Coast and 91 is the best you can get at standard pumps (unless can find and pay $9.49+ a gallon for 100 octane race fuel).

 

It says right on the fuel filler door that 91 is the recommended minimum (or something to that effect). Here in Ontario you can definitely get 93 if you look for it, but at most stations 91 is the top premium. I have been told a number of times that 93 is not worth the extra money.

 

Higher octane will make a ping

 

What kind of ping?

 

From my experience that I had. It makes the car run rough or not properly. And when you do hit the gas the car hesitates.

 

You must of gotten bad gas. Higher Octane gas does the exact opposite of what you just described on cars designed for it (including the C300 Coupe).

 

That is my understanding as well that the higher the octane better response time from engine due to faster ignition of the fuel...

 

Close but not quite correct. The higher the Octane the less likely the gas will spontaneously combust due to pressure instead of by the spark of a spark plug. The goal is to have the gas combust at the exact time that the spark plug fires. If it ends up combusting before that, you loose power and can potentially damage your engine.
The C300 2.0L engine has a relatively high compression ratio of 9.8:1. The high compression of the motor requires the higher octane gas for it to function properly.
The use of lower octane gas will cause pinging, engine roughness, loss in performance, and potential irreversible damage.

The use of higher than recommend octane does nothing as well. Since the goal is to prevent the gas from igniting prematurely due to pressure, there is a perfect Octane rating to achieve that - and the car manufacturer has already figured that out for you. Using any Octane rating higher than that won't get you anything because the gas is already igniting at the optimal time.

 

Sweet !

 

Its all in the details.....