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Thread: New roadtrip in the G4, much better hwy mpg than my 2014 hatch!!!!

  1. #11
    Moderator Eggman's Avatar
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    Quote Originally Posted by Dirk Diggler View Post
    Well drove from Atlanta to Charleston SC yesterday with my wife. We have the exact same tire and wheel on the G4 as on my 2014 hatch. I manually checked the mpg from Atlanta to Columbia SC and even factoring the 2.2% in revolutions on the larger tire we still netted 38mpg! And this is with me doing 70 to 75 mph the whole way with a lot of rolling hills in between. Meanwhile doing the same speed on the hwy is netting me 27 to 30 mpg on my 2014 hatch. I'm starting to think it's engine related?
    Might want to get your engine compression checked.


        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


  2. #12
    Senior Member dspace9's Avatar
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    Quote Originally Posted by Dirk Diggler View Post
    Yeah I should drive hatch on the hwy for longer than 20 mins to see for sure. I drive both Mirages the same though. I'll post results.
    It's the "jumping in the car for 5 minutes at a time" type of scooting around, that drinks more gas. Drive steady for an hour at a reasonable speed, in overdrive, and my Mirage'll milk gas big time.

    Worst for me is middle of the winter start up, the first 5 minutes I'm getting like 10 MPG lol. Then the engine warms up and I'm able to pull high 30s.

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 42.2 mpg (US) ... 17.9 km/L ... 5.6 L/100 km ... 50.7 mpg (Imp)


  3. #13
    Senior Member Dirk Diggler's Avatar
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    Quote Originally Posted by Eggman View Post
    Might want to get your engine compression checked.
    I'll try it. That's a symptom, bad mpg, with compression?

  4. #14
    Moderator Eggman's Avatar
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    Quote Originally Posted by Dirk Diggler View Post
    I'll try it. That's a symptom, bad mpg, with compression?
    Well, I'm no mechanic so take this advice with a grain of salt. But an engine's efficiency depends on all parts fitting together - not too tight and not too loose.

    From the Wikipedia article on Compression Ratio:
    Quote Originally Posted by Wikipedia
    A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air–fuel mixture due to its higher thermal efficiency. This occurs because internal combustion engines are heat engines, and higher compression ratios permit the same combustion temperature to be reached with less fuel, while giving a longer expansion cycle, creating more mechanical power output and lowering the exhaust temperature.
    Manufacturers design their engines to operate at specific compression ratios. Technology has allowed higher compression than in days passed. Compression that's too high leads to predetonation commonly known as knocking and pinging which can cause significant internal damage to a gasoline engine (diesel engines are designed specifically for this.) Ping sensors on today's engines detect predetonation and will retard ignition timing to avoid damage but in turn reduces efficiency.

    Predetonation can be caused by using poor quality fuel. Higher compression requires higher octane fuel to avoid predetonation. Turbo- and superchargers increase compression and can cause catastrophic damage in an engine not designed for it. Most normally aspirated engines (those without a charger) can easily operate on regular unleaded. High performance engines with high compression ratios and/or turbo or superchargers usually need high octane fuel.

    Compression ratios for internal combustion engines used to be a fixed number but nowadays technological advancements allow for variability. Modern variable valve timing has another added complication, though I doubt that would contribute to low compression.

    Low compression can keep an engine from making the best use of the air & fuel delivered. In other words, loose-fitting parts allow combustion gases to blow by the piston and/or valves instead of pushing the piston down, which is the goal of the internal-combustion engine found in our cars. This is usually indicated by low compression. Low compression can indicate wear on the cylinder and/or piston rings. Low compression can also be caused by valvetrain problems - for example, valves that are not seating due to damage, carbon buildup, or cam/rocker problems.


    So coming back around to your original concern, it sounds like your Mirage is consuming much more fuel than is typical for these cars. You are consuming almost twice the amount of fuel than I do on average. Airing up your tires and slowing down probably won't fix what's going on.

    27 to 30mpg indicates a real problem to me (from here.) Poor quality fuel can clog fuel injectors - stick to Top Tier brands and/or use a fuel system cleaner such as Techron on a regular basis to avoid deposits from fouling injectors. Change engine oil on a regular basis. Use a quality air filter - one that doesn't pose too much restriction on incoming air (but don't use a sponge K&N filter either.) If these things are being done and fuel efficiency is still a problem, get the compression checked - it could indicate a bigger problem with an engine.

    See also: Engine efficiency

    And sorry for the wordy reply. Hope this helps.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


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    Dirk Diggler (04-11-2021)

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    Moderator Eggman's Avatar
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    Hey Dirk one more question - how long in minutes is an average trip for you in your Mirage? Would you say your Mirage runs long enough to fully come up to temperature for most of it's trip? I ask this because lots of short trips at low speeds (say, to the corner store) kills fuel economy because the engine never reaches full operating temperature.

    dspace9 brought this up - it's worth addressing.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


  7. #16
    Senior Member Dirk Diggler's Avatar
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    Quote Originally Posted by Eggman View Post
    Hey Dirk one more question - how long in minutes is an average trip for you in your Mirage? Would you say your Mirage runs long enough to fully come up to temperature for most of it's trip? I ask this because lots of short trips at low speeds (say, to the corner store) kills fuel economy because the engine never reaches full operating temperature.

    dspace9 brought this up - it's worth addressing.
    Its a combination of short stops and twice weekly hwy runs about 20 miles each way doing 70 to 75 mph around 3200 rpms. I just put in a fresh fram engine filter and cabin filter. I mostly use non top tier detergent gas from Racetrack but I do use the fuel injection cleaners, about a bottle every 60 days. I need to drive on the hwy for about 45 mins and hand calculate mpg and see what happens. Otherwise the engine purrs like a cat at idle, no weird slapping sounds either.

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    Moderator Eggman's Avatar
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    Quote Originally Posted by Dirk Diggler View Post
    Its a combination of short stops and twice weekly hwy runs about 20 miles each way doing 70 to 75 mph around 3200 rpms. I just put in a fresh fram engine filter and cabin filter. I mostly use non top tier detergent gas from Racetrack but I do use the fuel injection cleaners, about a bottle every 60 days. I need to drive on the hwy for about 45 mins and hand calculate mpg and see what happens. Otherwise the engine purrs like a cat at idle, no weird slapping sounds either.
    That's good news.

    Just out of curiosity on your next trip to Charleston try staying in the slow lane and just do the speed limit. Watch your fuel economy gauge and let us know what happens. I would expect it to climb into the 40s.

    Is your reported 27 - 30mpg a general average number or just for your Charleston trip?

    Sometimes I miss Charleston though it's not the same town as when I lived there. I was in North Charleston just off Ashley Phosphate road. Nice place to visit.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


  10. #18
    Senior Member Dirk Diggler's Avatar
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    Quote Originally Posted by Eggman View Post
    That's good news.

    Just out of curiosity on your next trip to Charleston try staying in the slow lane and just do the speed limit. Watch your fuel economy gauge and let us know what happens. I would expect it to climb into the 40s.

    Is your reported 27 - 30mpg a general average number or just for your Charleston trip?

    Sometimes I miss Charleston though it's not the same town as when I lived there. I was in North Charleston just off Ashley Phosphate road. Nice place to visit.
    No we took the G4 for the road trip. The hatch I'll report later this week after doing some distance driving on the hwy. Yes, North Charleston has changed a lot. The hipsters are moving in droves and driving the older community out for better or worse. My folks live in Mt. Pleasant and its a none stop development. I'd live down there in a heartbeat, very burned out on Atlanta.

  11. #19
    Quote Originally Posted by Dirk Diggler View Post
    Meanwhile doing the same speed on the hwy is netting me 27 to 30 mpg on my 2014 hatch. I'm starting to think it's engine related?
    I wanna see you do an apples to apples experiment.

    Take both cars out at the same time and drive a loop back to the starting place. Include some freeway miles. Check tire pressure before you go. Both drivetrains have to be the same temp at the start (not one cold and one already warmed up). Using the same HVAC settings.

    Try to accelerate at the same rate. And the car in the back can't draft the car in front.

    I'm betting the onboard MPG display isn't going to show a ~33% difference between the two cars (even if they may be a few percent off in actual fuel consumption).

    I did something like this to see how my folks' former Civic hybrid compared against the Mirage in identical driving conditions.
    Thread: 2017 Mirage sedan vs. 2009 Civic hybrid MPG showdown!

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 63.2 mpg (US) ... 26.9 km/L ... 3.7 L/100 km ... 75.9 mpg (Imp)


  12. #20
    Senior Member Dirk Diggler's Avatar
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    Quote Originally Posted by MetroMPG View Post
    I wanna see you do an apples to apples experiment.

    Take both cars out at the same time and drive a loop back to the starting place. Include some freeway miles. Check tire pressure before you go. Both drivetrains have to be the same temp at the start (not one cold and one already warmed up). Using the same HVAC settings.

    Try to accelerate at the same rate. And the car in the back can't draft the car in front.

    I'm betting the onboard MPG display isn't going to show a ~33% difference between the two cars (even if they may be a few percent off in actual fuel consumption).

    I did something like this to see how my folks' former Civic hybrid compared against the Mirage in identical driving conditions.
    Thread: 2017 Mirage sedan vs. 2009 Civic hybrid MPG showdown!
    I took my 2014 hatch out today and did some scenic driving thru suburban roads. Never faster than 45 mph and it did well. The gauge actually crept up to 38 mpg, the highest I've seen in a year. I'm guessing my earlier readings were due to stop and go traffic to get to the hwy and then going 75 mph for 20 mins and then getting off my exit back to stop and go traffic, then parking at work.



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