How to improve gas mileage?
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Thread: How to improve gas mileage?

  1. #1
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    How to improve gas mileage?

    I've spent the last hour reading threads on gas mileage. Everything was old and pretty basic stuff, so I started a thread for more advanced tips.

    BACKGROUND: I just bought a 2008 Odyssey Touring with 158,000 miles. It does not have the run flat tires or the vcmuzzler. I went on a mostly interstate trip at 76-77mph with the AC on and averaged 21.5mpg for the 350 mile trip. Immediately prior to the trip, I changed the oil with Mobil 1 Synthetic 5W-30 and put in a new air filter. I run 40psi tires all around.

    QUESTION: What mechanical suggestions do you have to improve gas mileage. Please, let's avoid rookie stuff in this thread (e.g, drive slower, avoid fast starts). I'm thinking of 1) changing transmission fluid 2) doing a Seafoam engine treatment 3) changing the O2 sensors 4) pumping the tires up to 42psi 5) changing the spark plugs 6) removing the rear seats to reduce weight (not much advantage here, but I don't want the seats in the car so why not?) 7) adding an aftermarket power chip. Any other suggestions?

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  3. #2
    Registered User John Clark's Avatar
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    You need to take a look at fuel trims with a scan tool. I found that my van, while running OK, was adding about 10-20% more fuel...not enough to set a code but enough to affect gas mileage. Replacing all four O2 sensors fixed it. The OEM sensors are made by NTK and can be purchased at RockAuto.com for much less than the dealer and they're an exact match.
    2008 Odyssey Touring-Silver
    2011 VW Jetta SE-Black
    2002 GMC Sierra SLT LB Z71-Red
    1998 Nissan 200SX SE-Blue

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    Thanks. I was thinking of installing an OBD2 Scan tool and using it to fine tune my driving style. I'll check out the O2 sensors.

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  6. #4
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    Quote Originally Posted by WillowTheDog View Post
    Please, let's avoid rookie stuff in this thread (e.g, drive slower, avoid fast starts).
    drive slower

    and 7) adding an aftermarket power chip...

    are you serious? and you have the impudence to call physics 'rookie stuff'?




    as for increased tire pressure, I've owned and my dad still owns a TDI diesel, so I've been pretty active on the forums there; let me tell you those guys are pretty hardcore about fuel economy. anyways, there has been a few that ran high tire pressures, let's just say they don't anymore. unless you like saving a couple of pennies and replacing sets of shredded $500 tires.
    Last edited by bbarbulo; 06-12-2017 at 12:28 AM.

  7. #5
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    Buy yourself an Ultra-gauge or a Scan-gauge or similar for real time info and lots of it. O2 sensor readings,instant MPG, and a LOT more.
    Use the recommended spark plugs.
    Use the proper wt oil and use synthetic, like Mobile 1.
    Your oil recommended wt is 5w20 but I would imagine that a 0w20 full synthetic oil like Mobil 1 would be just fine. Your choice.
    Your owner's manual calls for Honda Z-1 atf. If it hasn't already been changed in the last 30k miles or so, I sure would recommend doing at least one drain and fill with the Honda DW-1 or another good synthetic atc, such as Valvoline MaxLife Dex/Merc atf (around $18 for a 1 gal jug).
    Check your PCV valve.
    Air filter?
    Power Chip???? You're kidding, I hope.
    On my '03, driving at 60 mph gives me around 5 mpg more than driving at 75 mph. Wind resistance on an Ody is a LOT.
    Buffalo4
    2003 EX-L
    179k miles orig tranny June 2017

  8. #6
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    Thanks for the suggestions. FWIW, I just provided my recent trip MPG to give posters an idea of the vehicle's current MPG. My 2nd tank of gas averaged 21.8 MPG with some combined rural and interstate driving (70-75). There doesn't appear to be a power chip for this vehicle, but I thought it was worth asking. I'm changing the trans fluid this week and it has a new air filter. Thanks for the suggestion to check the PCV valve. Where I drive, it's dangerous to go 60 mph on the interstate during rush hour. I've purchased an OBD2 scanner and hope to get instantaneous MPG to see if the change between speed and mpg is linear or whether it ramps up at a particular speed. I'm also curious to see how (or if) MPG changes when the ECO mode comes on.
    Last edited by WillowTheDog; 06-18-2017 at 06:09 PM.

  9. #7
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    Update. I received the OBD2 scanner to show instantaneous MPG. It was enlightening. Although I need to use it longer to get more feedback, it appears a major culprit with this vehicle is acceleration. Accelerating from a stop resulted in a drop to 5 mpg! I'm not talking about a jackrabbit start or even keeping up with traffic from a stop light. Anything faster than grandma driving to church resulted in a drop below 8 mpg.

    To put this in perspective, my Dodge QuadCab Ram 3500 diesel weighed nearly 6,000 pounds and didn't drop below 10 mpg on acceleration.

    Even at cruising speed, a slight acceleration dropped mpg to 10. On the other hand, fuel economy didn't seem to vary much whether I was driving 50mph or 65 mph. (I need to confirm that with a longer drive at each speed.) I haven't checked instant mpg at higher speeds yet, but I suspect it will drop logarithmically with speed.

    If I notice anything else interesting, I'll report back.

  10. #8
    Registered User John Clark's Avatar
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    Use your scanner to take a look at short term and long term fuel trims at idle, and at 2500 RPM. You will have a long term (LT) and a short term (ST) for both banks. Post those numbers.
    2008 Odyssey Touring-Silver
    2011 VW Jetta SE-Black
    2002 GMC Sierra SLT LB Z71-Red
    1998 Nissan 200SX SE-Blue

  11. #9
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    WillowTheDog,

    One of the main reasons that the mpg at first takeoff is so high is that it is in 1st gear.
    When you are going around 60 mph, downshift one gear and see how much the mpg changes.
    Being able to stay in that 5th gear makes a lot of difference. So, low gears equal low mpg, overall.
    And, yes, jackrabbit starts even use more fuel, but for a very short period of time.
    Buffalo4
    PS: For the best mpg, always drive downwind!!
    2003 EX-L
    179k miles orig tranny June 2017

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