Tweaking mileage by taking care of your car

Perfect tire pressure. A well-tuned engine. Clean air filters. These are in my experience, by far, the most common suggestions for reducing fuel consumption.

I think that hypermiling, telecommuting, and driving more fuel efficient (or better yet, electric) cars are all going to go way further in reducing our petroleum footprint, but for those who want to tweak things even further, what are some of the tips and tricks for dropping your fuel consumption just that little bit more? I'd love to see some numbers if you have them!

I have a 94 three cylinder Geo metro. On my last long (600 mile) trip i made 50 mpg @ no more than 65 mph.

I think all that fast driving costs you. I have read that every five miles over 55mph costs you 3% in fuel consumption.

On the Los Angeles city streets i drive the people behind me nuts because i don't drive fast just to get to a red light. Sometimes the car behind  me will change lanes just to be able to pull in front of me. To my mind all part of city sickness.

I had thought that California would be the one to drag the US to the electric car but I'm reading things about China.

Shawn Klassen-Koop wrote:Perfect tire pressure. A well-tuned engine. Clean air filters.

Man, those things that often get forgotten about can make a big difference, like those properly inflated tires and clean air filters. As far as mechanics go, fuel injectors often eventually get clogged, and an occasional dose of injector cleaner can really help. A few other simple things, keep those windows rolled up- open windows cause a lot of drag; and remove unnecessary items from the car/truck. Driving around with crap in the vehicle is just extra weight that can really add up, which requires more fuel to get from point A to point B.

James, would you have any estimates as to how much of a difference some of your suggestions would make?

My wife's car turns itself off at intersections.  Same could be done manually if trying to get a max mpg.

Weight removal (already mentioned)

Weight removal at wheel/tires(rotating mass and unsprung weight is several times worse than extra junk in the trunk). So lighter weight rims will give an improvement.

Skinnier tires would have less friction than wider tires.

Slightly talller tires would travel further per engine revolution, giving better gas mileage.

Underdrive pulleys. They spin accessories like a/c, power steering and alternator slower, thus putting less of a load on the engine.

Havent seen a conversion, but intermittent a/c would help. On for 30 seconds, off for 15. Same for alternator. Better yet, alternate between them. Only one on at same time.

Shawn Klassen-Koop wrote:James, would you have any estimates as to how much of a difference some of your suggestions would make?

Gosh I wouldn't know where to begin on how to calculate that. Sorry :/

wayne fajkus wrote:

Slightly talller tires would travel further per engine revolution, giving better gas mileage.

I tried this on a pickup truck years ago, and I experienced the opposite effect. It takes more torque to turn a larger wheel, and my gas mileage went down like 30 miles per full tank.

James Freyr wrote:

wayne fajkus wrote:

Slightly talller tires would travel further per engine revolution, giving better gas mileage.

I tried this on a pickup truck years ago, and I experienced the opposite effect. It takes more torque to turn a larger wheel, and my gas mileage went down like 30 miles per full tank.

I used the term "slightly" intentionally. It can be overdone. Other factors come in to play. Like swapping a truck to big mud tires that are taller, but wider and heavier than what was stock.  The weight and friction kick in on a negative.

But out of curiosity, were you able to adjust your speedo? It won't know the truck is travelling any further

wayne fajkus wrote:

But out of curiosity, were you able to adjust your speedo? It won't know the truck is travelling any further

Man! You're exactly right Wayne, my brain is out to lunch. No I never did adjust the speedo. I went from a factory 205/70/16 to a 235/70/16, so yes wider & taller. I remember the immediate loss in acceleration, and my brother mentioned I'd lose gas mileage because it takes more torque to turn a larger wheel, which is true too.

I think all that fast driving costs you. I have read that every five miles over 55mph costs you 3% in fuel consumption.

On the Los Angeles city streets i drive the people behind me nuts because i don't drive fast just to get to a red light. Sometimes the car behind  me will change lanes just to be able to pull in front of me. To my mind all part of city sickness.



Absolutely right.  Wind resistance is an exponential function of travel speed.  So a 5% increase in speed will mean more than 5% more wind resistance.  It depends on the vehicle how much more.

I have this little dongle that reports actual mpg used for each of my trips. I find that watching the data is the best way to figure out how to increase the efficiency of your vehicle. Each one is going to be different. For my truck, it's all about how much it's loaded down. For my R32, it's all about staying between 65-70mph. I have not found tire pressure, windows, or any of the popular "hacks" to make any material difference whatsoever.

Although, to be honest, my biggest piece of advice for people wishing to reduce their petroleum footprint with relation to cars is to buy an old car. The car that doesn't need to be manufactured is going to use several lifetimes less petroleum that the new one (electric or not) that needs to be manufactured (from resources mined elsewhere and shipped), shipped, built, shipped, shipped, shipped, shipped, and shipped some more. Or just reduce the amount you need to drive.

Recently I had my main vehicle start having serious issues... and when five different mechanics couldn't figure out what was wrong with it I started learning about cars myself.

I started by reading an old book on how engines work and then continued by watching youtube videos and ended up on Shcrodingers Box. His videos on fuel trims were fantastic. Between them, a cheap obd2 usb dongle, a multimeter, and my cell phone I was able to think about what was happening to my vehicle, consider the potential issues, and then check the appropriate systems.

During that process, I ended up cleaning a lot of components.

I have never really worked on cars... but I managed to track down the main problems and, in the process, increase my mpg from a 15ish to 18ish. I know that isn't much... but it is a solid 20% increase. While the car was having issues the mpg was sitting down at around 10...

In addition to the mentioned air filters and such, just a little knowledge is all it takes to do a few extra things such as cleaning your mass air flow sensor and throttle body intake. If you are comfortable with doing so and have an older car you might also consider taking apart the throttle body, egr valve, etc. and using a brush to take the carbon build up out of them (my car had the egr to throttle body hole mostly plugged up with carbon...)

Anywise, just watching the linked youtube channel above (especially the fuel trim videos) let me increase my mileage significantly.

Thinner tires should help a lot (but one should be cautious as reducing friction means slower/worse breaking... and tire structural strength could become a serious concern). Part of the reason trains work so well is that their tires only touch the tracks slightly.