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Guest Message by DevFuse

Get you C-MAX Hybrid Registered in the official Ford Authorized Registry. More here.


How many miles did it take to notice improved fuel efficiency?

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21 replies to this topic

#21 OFFLINE   MrGreen29


    New Member

  • C-MAX Hybrid Member
  • 4 posts
  • Region:U.S. Pacific Coast
  • LocationLos Angeles
  • My C-MAX's Year:2015
  • Current Vehicle:Cmax hybrid

Posted 09 March 2016 - 12:56 PM

I've only had my car for about 18 days. I've filled up once with half a tank and got 42.3 calculated and filled up a second time from near empty which was calculated at 39.2. I definitely know I have a ways to go. Hopefully i see some improvement when the weather warms up!

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#22 OFFLINE   RobMax


    C-Max Hybrid Member

  • C-MAX Hybrid Member
  • 159 posts
  • Region:U.S. Pacific Coast
  • LocationSunnyvale, CA
  • My C-MAX's Year:Decline
  • Current Vehicle:2013 Sterling Gray Metallic C-Max Hybrid SE

Posted 27 March 2016 - 12:27 PM

From what I heard. If your car is built for 87- or 89-octane gas upgrading to premium won't do you any good. In fact, it could even harm both your car and the environment, since more unburned gas will get into the emissions system and interfere with its ability to prevent noxious discharge. That unburnt gas will drip out your tailpipe on the road and pollute the environment.


This myth needs to be dispelled. Octane rating is nothing more than a number to help differentiate how much compression the fuel can withstand before spontaneous combustion (aka uncontrolled explosion) in the cylinders occurs. The lower the number, the less compression it takes before 'boom' happens.


Good example: My Dad's old 71 F-100 pinged (aka experienced uncontrolled combustion events) on anything less than 91, even though the engine was built for 87. As it turned out, things got old from carbon build-up, gummed up rings, etc, and it caused uneven firing on decreased octane fuel, but it ran well on 91. No big deal. 


Modern vehicles also have knock sensors to help burn efficiently for different octane mixtures. Plus, you could dump a whole lot more unburned gas into the exhaust stream and modern emissions controls (i.e. catalysts) will cook off any excess hydrocarbons, CO, and NOX. There will be no "gas dripping out your tailpipe" unless you happen to have a fuel injector stuck open or some other major problem that the engine and/or emissions systems just couldn't compensate for.

Edited by RobMax, 27 March 2016 - 04:17 PM.

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