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Gas mileage mods?

Discussion in 'Car Forum' started by AnalogKid, Apr 26, 2008.

  1. AnalogKid


    Jan 22, 2007
    Am starting to think of trying some mods to see if I can increase gas mileage and would love some feedback.

    Does changing the air filter to a K&N high performance filter really improve mileage? Would an entire airflow kit work better? As it is my standard air filter is amazingly clean even after 9 months of use so I'm not sure what the deal is. Am I getting enough air flow currently? I know it's an odd question but the fact that the air filter is so clean still just seems weird.

    Got 40,000 on the current set of spark plugs but they are pretty clean and not fouled at all so not sure they are a problem. Could change them out but I do it in Fall regularly. Do new plugs really make a difference as I haven't noticed any problems this past year?

    Also, my idle seems a bit high but I don't know that I want to mess with it as there is no problem with "coughing" or sputtering or stalling and lurching. Don't really want to "fix" something if it's working good but would lowering the idle make a noticeable difference in gas consumption?

    Is there such a thing as a broken thermostat that affects cooling? Meaning, my gauge has dropped to below C for cold so I don't know if it's a broken gauge or if the thermostat is messed up. I'm used to thermostat issues having to do with overheating so I'm confused on this one. The water pump (knock wood) seems fine.

    Thanks much to anyone who has advice.
  2. Berto

    Berto woo woo

    Sep 15, 2003
    Keep your tires near max inflation.
    It seems obvious, but i swear every other car I see in traffic is running low on tire pressure.
    The KN stock filter has worked for me, I shortened the air tunnel and bypassed the resonator box. The tradeoff is more intake noise.
    I wouldn't play with idle setting.
    Lighter weight wheels and tires would help too, though the investment is probably not worth it.
    Reduce unsprung weight. If your car is loaded with crap you don't need, remove it.

  3. I'm assuming you have a fairly recent car. Fuel injection and a Power Control Computer.

    No. A better flowing filter and intake could help increase POWER, but not fuel efficiency. The MAF/Computer ensures you get the right amount of fuel for whatever air is making it to the engine.

    If you change them every couple of years anyway, then that's plenty. If there's no noticeable erosion or deposits on the plugs, then they are probably performing as intended.

    If it's a modern car, I wouldn't mess with it. In many cases, idling at 700 rpm is more efficient than idling at 500 rpm... it's just the right speed for that engine, timing, intake, exhaust, etc combination. I'd trust the engineers on that one.

    Yes, a thermostat can fail in a way that prevents the engine from warming up to its proper operating temperature. Running too cold will have an adverse effect on economy (and performance.) Is the problem the thermostat, the temp sensor or the gauge? (In many cases, it's easier to replace the thermostat and temp sensor than the gauge, if that's how you like to troubleshoot problems:) )
  4. filthy infidel

    filthy infidel 100% Infidel

    Apr 24, 2007
    North Carolina
    Islandhopper is right on all counts except the idle speed thing. A gasoline engine idling is a working vacuum pump, working at higher speeds is detrimental to fuel economy.

    MOST modern vehicles will illuminate the CEL with a P1137 or similar code "coolant below thermostat threshold".

    Most modern spark plugs are good for five years or 100Kmiles, and after that could likely be fused to the da^^n head.

    Most of my customers that call back saying that their car runs with a 'lot of zip' after a 'tune up' are right- because I brought their tire pressure from twenty psi back up to thirty five psi.

    And leave the intake system ALONE. If you want to install a K&N filter, fine. You will likely trash your MAF. The 'intake systems' are another story. I have seen quite a few that destroy the engine. They are not designed to fit well and certainly not to last. Most fit poorly if at all and when they fall off then the engine is ingesting an abrasive air/grit mixture and wear exponentially faster.
  5. Lone Wolff

    Lone Wolff Tire World...

    Dec 17, 2002
    Definitely replace that thermostat.

    For some reason I have to replace mine every 3 years or so on my 94 Mazda B4000. I've tried 3 or 4 diff brands, always the same result. When mine fails, it always fails in the open position and runs WAY to cold.

    I get ~20 mpg when mine works right, and about 16 when it doesn't. That's approx 25% difference. YMMV.
  6. AnalogKid


    Jan 22, 2007
    Found out why my temp gauge is broken--a squirrel chewed thru the wire from the sensor to the gauge. Odd I know. Still, it explains why I had to chase a squirrel away from my car so often and why the wire had all these little teeth marks on it. Kind of funny, but wasn't fun to fix.

    Adjusted the timing and gonna try a few more things. Thanks much for the advice everyone.
  7. Hauptmann6


    May 22, 2002
    Portage, MI
    Better to fail open than closed. You can get home to fix it if it's running too cold.
  8. JDSTG58


    Feb 4, 2008
    + 1 on that. I had a 96 ford Ranger that had the same prob. MPG went from 17 to 12. It was just the thermostat.

    If you want to improve MPG and your car is in good shape, tuned up, make sure :

    tires are properly inflated. The higher the pressure the better MPG, but too high will cause tire wear, and can be dangerous.

    Have a clean air filter... Hi flow only helps power not MPG

    Remove as much weight as you can... Dont keep heavy unneeded stuff in the car.

    And most important... Stay off the skinny pedal:wavey:
  9. targetterror


    Apr 18, 2008
    The best mod for better gas mileage is your right foot. No quick starts and no high revving works quite well to conserve fuel. It's no fun, but it is cheaper.
  10. filthy infidel

    filthy infidel 100% Infidel

    Apr 24, 2007
    North Carolina
    BTW, E-85 (85% ethanol <alcohol>/15% gasoline) is an automotive industry SCAM.

    The primary difference between a normal gasoline burning vehicle and an E85 vehicle is 1) a fuel type sensor, 2) larger injectors, 3) modified PCM, and 4) stainless steel fuel hardware, because the alcohol handily contains water and is corrosive.

    A gasoline burning vehicle strives to maintain 14.695 to 1 ratio by weight, the higher number obviously the air weight to fuel weight ratio.

    When the fuel type sensor or oxygen sensors go lean (dependant on the model year/fuel strategy) the system will increase injector pulsewidth and thus increase fuel trims, richening to around a ratio of 9.6 to 1 air/fuel.

    So you are now burning MORE fuel per mile, and BTW Ethanol has about 66% LESS BTU per gallon that gasoline.

    A manufacturer cars based on the 'feature', fuel manufacturers sell E85. You buy both, they win, you don't.
  11. tjf76

    tjf76 CLM

    Mar 16, 2004
    Western Montana
    Good to know
  12. DriBak

    DriBak GUNS UP Millennium Member

    Jul 4, 1999
    West Texas
    Use the 1/3 rule. Drive with a light foot as so your RPM's do not go higher than 1/3 of your redline. I have achieved 2-3 mpg increase
  13. You could get real serious and take it to someone that knows how to "hack", or tune, the factory engine controller. I've heard of some pretty impressive mileage gains by leaning out the fuel mixture. As long as the tech knows his stuff, I mean really knows his stuff, it can be done safely. A lot of the newer GM cars are coming from the factory on the rich side, I guess because it's safer to be rich than lean, so there are gains to be made there. Of course, it's probably going to take way too long for the added mileage to pay for all the fuel and dyno time needed to get it right.
  14. walkin' trails

    walkin' trails

    Apr 24, 2005
    I have run K&N filters in both V-6s and 8s. The V-8s probably gained some power from better air flow, but I saw the best improvement from running one in a V-6 Windstar. Mileage went up with it.

    I picked up marginal gains running a cat back aftermarket exhaust on my '03 Expedition a couple of years ago. Highway mileage improved a bit, but around town seems to have suffered a bit.

    Its arguable, but synthetic oil in the correct factory weight seems to reduce friction.

    I've heard all the claims regarding the tuners that you can buy an reprogram your vehicle's computer. Some claim some impressive mileage gains. I'm not sure that they warrant the $400+ cost
  15. superman79


    Mar 3, 2006
    Try using air intake filter, Iridium plugs and high tension wires. This will improve your gas consumption a lot!
  16. 98_1LE


    Oct 17, 2005
    Under-drive crank pulley
    Free flow exhaust
    Alignment with near or zero toe.
    Narrower tires that are the same height.
    Read up on how to drive for better efficiency and economy (aka hypermiling)
  17. Kevin108

    Kevin108 HADOKEN!

    Mar 2, 2005
    Virginia Beach, VA
    Beating the EPA - The Why’s and how to Hypermile

    This is where I started. I don't use all the trick in the hypermiler's handbook but I've upped my tank average from 29 to 33 and I've had trips as high as 50 mpg.

    The top 3 tricks:

    1. Check your tire pressure. Most hypermilers pump their tires up to the maximum sidewall pressure, which is printed on the tire.
    2. Do the speed limit. Besides being illegal, exceeding the speed limit usually wastes more gas.
    3. Coast intelligently. There's no reason to stay on the gas all the way up to a stop sign or all the way down an exit ramp. Some hypermilers shift to neutral or even turn off their cars, but just coasting even in gear will save a significant amount of fuel.
  18. Geeorge

    Geeorge Sarcasm Inc.

    The best gain I got recently was changing my 2001 s10 from 5w30 Mobil-1 to 0w30 mobil-1.Picked up over 1.5 miles to the gallon ,and I was stunned:wavey:
  19. Kevin108

    Kevin108 HADOKEN!

    Mar 2, 2005
    Virginia Beach, VA
    How's your pressure with the thinner stuff?
  20. zotz_G23

    zotz_G23 LUDU President

    Aug 5, 2009
    b4 i went into the "heavily modded" stage in my truck, i got 2mpg better when i went with a new intake