(We initially ran this article on increasing your gas mileage in November 2015. In light of recent events in the Southeast, we thought it might be a good time to bring it out again.)
Would you be willing to save money if you could do it without significantly changing your lifestyle or behavior? Spending less on energy costs is “easy money.”
While gas prices are relatively low compared to previous years, the US Energy Information Administration still lists the average household gas cost for 2015 at $1962. Adding 10% to your miles per gallon can add up, and makes an even bigger difference as gas prices rise. Even at current prices, a 10% increase in gas mileage can net you annual savings of almost $200. A 20% increase leads to almost $400.
Plus, increasing your gas mileage means fewer trips to the pump. That’s better for the environment.
Three culprits keeping you from getting your best gas mileage are tire pressure, “junk in the trunk” and driving style. Tweak those three inexpensive items and you can easily increase your fuel efficiency by 10%. Make a few more technical changes, and you may raise your gas mileage by 20%.
Easy MPG Tweaks for Non-Car People
Properly Inflate your Tires
Car manufacturers set a recommended tire pressure for cars based on a combination of factors: comfort, braking, handling cargo capacities, etc. Most tires have higher maximum tire pressure ratings than the car manufacturers’ “suggested” tire pressure.
The standard recommendation is “properly inflated” tires. I have been running my tires at the tire manufacturer’s maximum recommended level, though the government recommends to go with the car manufacturer rather than the tire manufacturer.
A representative from Michelin corporate once told me that “a lot of science and engineering went into determining the maximum tire pressure ratings for their tires.” He strongly suggested never running tires above those maximum ratings. That’s good enough advice for me from the “Michelin Man.”
Conventional wisdom is that proper tire inflation means a 3% gas mileage gain over underinflated tires.
Junk in the Trunk
Here’s a gas mileage glutton that I need to work on: I carry a bunch of things in my car that really need to go in my garage. Tools and materials from recent projects accumulate in the back of my mid-sized SUV. I currently carry hundreds of pounds of stuff that I need to clear out. Considering you lose 1% on gas mileage for every 100 pounds of extras you lug around, I may have lost 5% of my miles per gallon hauling unnecessary items.
I’m not alone. It’s easy to leave things in your car. Keeping a gym bag or a few extra toys in your car doesn’t make much of a difference. If the weight is significant, it’s a good idea to unload and store your items somewhere other than your car.
External storage can also reduce your fuel mileage, If you carry a roof storage bag you aren’t currently using, you are unnecessarily losing some serious gas mileage. A rooftop kit may only cost you 2-8% of your gas mileage in town. At highway speeds you can lose up to 25% of your gas mileage by reducing the aerodynamics on your car. Rear mounted systems are more efficient (well, less inefficient) and only cost 1-2% in additional gas in the city and up to 5% highway.
Say No to Aggressive Driving
Fuel economy goes down 7% for every 5 MPH increase above 50 MPH. Cruising down the highway at 80 is a pretty good way to ensure that you aren’t getting good gas mileage. If you want to maximize your miles per gallon, take your cues from the Sunday drivers, not the stunt drivers. Drive like Grandma.
I understand that 50 MPH may not be practical on an interstate. Much as I like a leisurely driving speed, even I have to jackrabbit up to 65 on I-40 just to stay safe in traffic. I try to recognize that following the speed limit increases safety and saves a lot of money, and adjust my driving accordingly.
In town it also makes a lot of financial as well as safely sense to drive less aggressively. Gentle acceleration from stops can save another 5% in gas mileage. Is a fast start from the stop light really going to get you to your destination faster? Or will it just increase the chance that you’ll bump fenders with the car in front of you and spend extra money?
MPG Tweaks that Require Some Automotive Knowledge
Proper Oil Viscosity
Conventional automotive wisdom has been to run heavy weight motor oils in older cars with lots of miles on the engines. My current vehicle has a recommendation of 5-30 weight motor oil. I have 158,500 miles on the car and like to run a 10-40 weight synthetic blend in the sauna that is a central NC summer.
In the winter, though, I mostly do short-trip driving, so I am going to switch to the manufacturer’s recommendation of 5-30 weight and go with a full synthetic. I plan to take advantage of a local part store special on the oil I need and a filter to do a winter oil change and see if I get any noticeable gains on the fuel mileage readout. The less viscous oil creates less drag on the engine parts, which is good for a few percent on gas mileage.
A Tune Up for Better MPG
Currently I am not getting quite the gas mileage I got when my SUV was new (at least new to me.) On my last trip out of town, I noticed my gas mileage clocked in around 25.8 MPG. That was significantly down from earlier years, when I had gotten around 29.7 MPG driving 60 MPH in eastern NC. (I know, nobody drives 60 MPH anymore. Yeah, I’m that guy in the slow lane.)
My SUV still runs very well, but there are a few tweaks I’d like to make so see if I can get back to my previous numbers. I don’t think it needs any plug wires or changes to the computer controlled timing. With over 150,000 miles on the engine, it’s probably time for some new spark plugs.
I want to try the Bosch Platinum +4s, which are supposed to improve fuel economy. If I install a set, will I get any increase in mileage? (editor’s note: He did! See Replacing the Spark Plugs for Better Gas Mileage.) Replacing the plugs will run around $24 for 6 plugs if I do the work myself.
I suppose the oxygen sensors may not be doing as good a job with over 150,000 miles. My 2002 SUV has two oxygen sensors that are in front of the catalytic converters: one per side of the V-6 engine. The oxygen sensors measure the exhaust gas and adjust the air fuel ratio accordingly. As they age, they don’t effectively measure the exhaust gas as accurately. That causes the fuel-air mixture to be more rich (using more gas).
It will cost me about $50 to replace the sensors, doing my own work.
There are new synthetic gear oils that are available and appropriate for use in differentials. Heavy weight or high viscosity gear oils have the consistency of molasses in cold weather.There should be some efficiency gains from switching to a lighter weight multi-viscosity synthetic gear oil for the differential in cold weather.
My SUV has a rear differential capacity of about 3 quarts. At about $10 per quart, this should cost about $30 or so for most DIY car folks. It can cost significantly more at a garage or lube shop to change out differential gear oil, though. This is probably not a high return on investment activity if you have to let a garage do it.
Just a Note
Many of the tweaks I’m going to try are much cheaper to implement if you can do them yourself. When in doubt, leave it to professional mechanics. If you’re a rookie car do-it-yourselfer, getting some help from more experienced car enthusiasts may be necessary to do work efficiently.
If you don’t want to do the work yourself, a standard tuneup can run anywhere from $50-$200, but will increase the life of your car in addition to increasing gas mileage. And increasing the life of your car can save you even more money than tweaking your gas mileage.
Increasing Gas Mileage isn’t Complicated
I think the combination of all these suggestions should yield a mileage gain of 10% or more. My goal is 33 mpg highway. Hopefully, I don’t have to drive 50 MPH to achieve that goal.
Increasing your gas mileage doesn’t have to be difficult. Even if you avoid making changes to your car by changing your oil and tuning up the engine, you can see big gains in your gas mileage by keeping your tires inflated, not hauling around extra weight and driving more conservatively. When you look for painless ways to save money, increasing your gas mileage with a few minor changes is a good way to start.
Jon has worked on cars as a hobby since he was a boy. His varied work history includes working as a professional mechanic for a national tune-up/lube company back in the mid ’80s. He still does most of his own maintenance and will talk cars for hours.
Do you think about maximizing your gas mileage as you travel? What tweaks do you make to get the best mileage possible?