Do cars with manual transmissions get better gas mileage?

Chris D has it right. It's the fluid coupling (called a "torque converter") that is the culprit in most automatic transmissions disadvantage in fuel mileage.

As he says, there is slippage when an automatic changes gears. Once you are under way, most modern automatics will lock the torque converter so that there is no slippage, but the control computer is usually programmed so that the slightest grade causes it to unlock, and in some conditions, to downshift.

All else being equal, staying in the highest gear practical gives you the highest fuel mileage. There are two main reasons.

-Friction is more a factor the faster the engine is running. Keeping it in a high gear lowers rpm and thus friction.

-Your internal combustion engine is an air pump. It sucks in air to mix with fuel to burn, and then exhales the products of that burning. A higher gear requires a bigger throttle opening to maintain speed, which is less restrictive.

Let me 'splain

The larger the opening letting air into your engine, the less work it has to do to suck it in. Try breathing just through a soda straw if you want a demonstration.

It might seem that a wider throttle opening would burn more gas, but it does not. At the same speed you burn the same amount of fuel to overcome the drag of the wind, friction in the drive train, and rolling resistance of the tires. The only other factors are internal friction in the engine, and intake restriction, both of which are optimized in the highest practical gear for conditions. A manual transmission gives you absolute control over what gear you are in.

Good Luck and Good Motoring!

Manual Vs Automatic Gas Mileage

Yes, they lack the Transmission required by an Automatic vehicle to do shifting. A transmission weighs 500-800 pounds, making manual cars significantly lighter. as well as the added control of the speed of the idle when you are in drive that a manual driver has.

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Technology is getting better for the automatic transmission, but new specs are supposed to be more true world for mileage expectations. The truth is, a lot of people really don't know how to drive a stick for economy, they think stick is for better performance. You can't have your cake and eat it too. Give me 2 cars, one auto, one stick, with the same number of speeds, and same final drive ratio, and I can get fractionally better mileage out of the stick every time, by driving for economy. However, if you have a 4-speed stick, and a 5 or 6-speed auto, the auto will do better. Sometimes, comparing the stick to the auto is like comparing apples to oranges.

In general, yes. The manual trans is a direct mechanical link from the engine and it allows the driver to shift gears to more efficiently use every unit of power. An auto trans is basically a big hydralic pump and some energy is lost because of that. Also, in an auto trans, you don't have the same degree of control. However, the difference is ussually minor (a couple of mpgs or wheel hp). However, if you know how, those minor differences can be expanded in you favor.

Yes, manuals typically get better gas mileage than an automatic because you are in full control of the gear you're in.

Yes they do (if properly driven). Automatic transmissions rely on a fluid coupler to connect the engine to the driveshaft. There is always some sort of slippage resulting in wasted energy. A manual transmission is directly connected via a clutch which offers no slippage unless it is defective.

Technology is just getting better. Autos used to be 3 speeds or maybe 4 speeds. Having fewer forward gears meant having to accelerate more before being able to shift into the next gear. But now with 5 and 6 speeds becoming common, coupled with smoother faster shifting, they are able to get better mileage.

Yes, no question.

Lower revs on gear changes for a start. Lower energy loss between the engine and the transmission.

and they are more fun to drive.

I would say they are the same but all of the new fuel efficient cars are automatic