How do I get the most mileage out of my manual-transmission car?

Is this a scientific exercise, or are you trying to get a measurabe improvement in gas mileage? When driving a manual, you want to keep it in the highest gear that you can, given the traffic conditions. The most economical gear is 5th. The difference between driving like a gas saving loon, and driving like a person, might be 5 gallons annually. Certainly in a 2002 Honda. Keeping your tires inflated to the correct PSI, staying up-to-date on your tune-ups and not jackrabbiting at starts will save as much gas and you won't be sitting there doing computations in your head.

There are two kinds of, let's say program, governing your car's engine. 1) There's the electronic computer that is hooked up to sensors (air, temperature, o2 levels post-combustion), and there is the http://www.hondapartsunlimited.com/parts-catalog/honda/accord-parts/2002/4dr-ex/ka4at/engine/camshaft-timing-belt (number 11 in the linked diagram), which mechanically controls the valves on each cylinder. The two of these - the electronic computer and the camshaft - determine the nature of the combustion in the cylinder. The computer is flexible in what it does, while the camshaft is fixed. It's just a rotating piece of metal. However, the results of the controls exerted by each of these systems changes at different RPMs. The computer, being flexible, will mostly try to optimize the combustion for a balance of fuel economy, performance, and low emissions, with this balance largely determined by the manufacturer, and somewhat determined by the state of the engine (engine computers can adapt to engines that have problems, and some can adapt to a driver's long-term habits). The camshaft, being the hunk of machined metal, is inflexible. As it rotates, lobes on the shaft push valves open: to let air into the cylinder, to let the burnt fuel and air (combustion products) out. When a lobe no longer pushes a valve open, a spring pushes the valves closed (to trap air and fuel under pressure). Inefficiencies at high RPM come in part because the valves have mass and springs can only close them so fast. Now, here's where it gets interesting. The timing of the opening and closing of the valves is determined by the shape of the lobes on the shaft and by the speed of rotation on the shaft. The slower the shaft rotates, the slower the rate of opening and closing of the valves, and the longer they remain open and closed. So at low RPM, the valves are behaving in a predictable way. At high rpm, the valves are opening and closing much faster, and the time where the cylinder has all valves closed is shorter. At high enough rpm, the valves can no longer shut quickly enough, or open long enough, for a perfect burn. Instead of clean air and fuel and a spark in a closed cylinder, for maximum bank, it may be a mix of clean and dirty air, with some valves still partly open, for a less efficient burn. So ... you've got the computer and the camshaft, the engine speed, and we haven't even gotten to the manual transmission and aerodynamics yet ... Broadly speaking, you will get your most efficient ride at an RPM in the middle of the car's "power band," which is, on a non-turbocharged and non-supercharged car like an Accord, determined by the shape of the lobes on the camshaft. You will, at this RPM, get the best results rolling well under 65mph, to minimize aerodynamic drag. You will, again at this RPM, get the best results at the highest gear comfortable for the engine (no lugging or knocking). tl;dr engines are complex, but the middle of the power band is where the components are most likely balanced out for maximum fuel efficiency.

Thirding a ScanGauge II reccomendation. One of the best Christmas gifts MrsEld has ever gotten me. I improved my mileage very quickly. I did have to manually program in either the instantaneous or trip MPG gauge calculation however, I forget which one. It was simple and you'll be able to figure it out no problem. I was just surprised that it came with one and not the other...

One common mistake I hear people making is shifting into neutral to coast. Not only does that cause you to be out of gear in case of a necessary evasive maneuver, but your car will shut off the fuel injectors while coasting in gear. As long as the rotational velocity of the wheels can keep the engine turning, the engine will need less/no fuel to turn. If you shift into neutral, you're consuming just as much gas as idling at a stop light.

According the manual on my car 2000-2500 rpm is the ideal for reducing gas consumption. The bonus of a manual transmission is that you can more quickly change gears and remain in this sweet RPM window easier and faster than an automatic transmission. Cars are geared differently, but for my 6 speed, if I'm city driving, stop light to stop light, I tend to stay in 3rd or 4th gear to keep it around 30 mph. Of course, interstate driving is what the top gear is designed for and because I've got 6 gears instead of 5, my 2500 RPM results in a slightly faster MPH than my previous manual transmission. I was also told by my dad when I first started driving that using the clutch to hold your car rather than the break is extremely expensive. Because it wears out the clutch faster, it means that you have to replace the clutch and it's way cheaper to replace brake pads than clutches.

The "highest gear possible" theory is overly simplistic. If you buy an OBD scanner ( mine cost about $20 and bluetooths to my android ) you'll often see that there is a "load" graph available. You want to keep the load as minimal as possible because that is where it's taking as little fuel as possible to keep the engine turning over. Without a scanner, it's a case of using your common sense - if the engine feels like it's struggling to cope then you should be in a lower gear. There will be a sweet spot but it's going to vary on lots of things so it's not as simple as telling you "change at 2000rpm". The coasting thing varies depending on the car (in my experience). My 12 year old Toyota Corollas (small petrol VVTi engines) get a better fuel economy out of gear. My 8 year old diesel pug gets massively better economy if you leave it in gear when you coast. One of the things that I believe hypermillers tend to argue ( or did last time I checked ) was that you should accelerate like you have all the time in the world. In my experience, you get better economy by being brisk and getting to cruise speed. This is a judgement thing and will change a lot based on traffic, how far you can go before slowing down, your car, etc, etc... The most important thing though, as far as I've seen (after keeping your car in good condition), is keeping your cruise speed to somewhere around the speed that they publish highway fuel economy stats for ( ie, if they base stats on 70mph, aim for 70mph ) because car manufacturers seem to tune cars for economy at around those speeds. My pug gets great economy at 70mph but really sucks at 80. (on preview, waaaay too long)

I am really uninterested in whether it is worthwhile to coast to a stoplight/down a hill vs. using the engine to assist braking. http://metatalk.metafilter.com/21568/Wild-guesses-do-not-fix-cars I do however think that it's coming together for me regarding what kind of shifting behavior I should use to maintain maximum fuel economy. I should be driving in the highest gear possible, provided that I am also in the power band for my engine, no? I think my problem here was a misunderstanding of the term "power band" which I took to mean "optimal RPM". It sounds like for all intents and purposes the power band is actually a pretty wide RPM range in which the engine is neither threatening to stall nor screaming as hard as it can. If I am able to drive along without having to put a lot of pressure on the pedal just to keep the car going at the speed that I want, then I am in the power band. As long as a light touch on the pedal is sufficient, I'm good. So I should be driving in the highest gear that allows the car to cruise along with only a light touch on the pedal. Is that correct?

This is all N=1 and your car may be different, but... A while ago I bought a http://www.plxdevices.com/product_info.php?id=GSSTBLUETOOTH. Combined with my smart-phone and http://torque-bhp.com/wiki/Main_Page, I was able to monitor instantaneous-mpg-over-time on a graph. Using this combo, I learned some things about my car (1999 Audi A4, 2.8 V6, Manual) and how it uses gas. I had thought that on the highway coasting-in-gear would be best, but I learned that coasting in neutral gave significantly better mileage (one can, of course, debate the safety of this practice). After a watching a while, I ended up simplifying everything I saw into: "Minimize the number of revolutions the engine makes". In practice, that means: - coast down hills out in neutral - use the highest appropriate gear (while avoiding bogging down too much) Taking the extra hyper-miling step of "alternately surging up to speed, then coasting down in neutral" gave even better mileage. On the other hand, it's quite annoying to anyone else in the car - and probably to cars behind too. I don't do that much.

Lower RPM = fewer combustions = less fuel used, right? Possibly a bit more abstract than what you were looking for and someone like Brockles, who has MUCH more practical knowledge than I do, can feel free to amend/correct me here. Oddly enough the mechanical engineer in me would rather you consider another aspect of this interaction. Instead of thinking in terms of lower RPM meaning less fuel used, think about the torque (at the tires) required to maintain a given speed. That torque has to come from somewhere and, all other things aside, is a constant. Where does it come from? There is no magic energy fairy in a car. Energy has to be converted to work and transferred to the street or 'da car no go. So, fuel right? It comes from the fuel. Fuel (potential chemical energy) --> combustion (chemical reaction) --> pistons/crankshaft (kinetic mechanical energy) --> transmission --> differential --> tires/road (frictional force) with heat being produced as a waste byproduct of combustion and drivetrain friction. Let's imagine a car with an engine that has an infinitely wide optimum powerband, that car will get the best mileage (at a constant speed) in the highest gear possible. Why? Because the friction and inertial losses in the engine (as heat) will be at their lowest Lower engine RPM means less internal movement and frictional losses (along with wear and tear I would think as well). At the same vehicle speed the same amount of energy will be transferred to the tires but, in a lower gear/higher engine RPM, more fuel will be used. This difference in fuel is all being wasted as frictional heat/losses. So, why not run in 5th gear all the time? Stoplights and the nature of IC otto cycle engines are why. These realworld engines have a powerband that's only so wide. You have to turn that low torque @ high rpms in the otto engine into higher torque at lower rpm at the tires to get moving from a stop. The price you pay is the need for a transmission of some sort and subsequently higher engine RPMs. So, long story short: Highest gear possible as quickly as possible while not straying from the vehicles powerband or accelerating too quickly (both of which can cause the ECU to push excessive fuel to the cylinders because it thinks "You need Powar now! Right boss?").