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Does your transmission have an impact on your vehicles gas mileage?

by Luke Wilhoit Consultant

When shopping for a car, you want a well-priced vehicle and one that will cost you less when it comes to maintenance. Gas is, perhaps, the most prominent car expense in your car ownership journey. As such, you might want a fuel-efficient car to make your car ownership experience affordable.

In a world where automotive manufacturers like GM are scrambling for fuel efficiency, manufacturers have gone heavy on hybrid technology, turbocharging, gasoline direct injection, and downsizing engines. In addition to this, in a quest for better fuel economy, manufacturers have been keen on achieving better gas mileage by taking advantage of the transmission gearing. 

So, this leads to the question: Does the transmission of your vehicle affect fuel economy? Does it matter whether your transmission is manual or automatic? Does the transmission fluid affect fuel mileage? What about the number of gears? 

Behold the facts.

Manual vs. automatic transmission

The fuel efficiency battle between automatic and manual transmissions is an eternal one. However, traditionally, manual cars have always won the title of the most-efficient. But is this the case today? 

Your friends or relatives have probably had their opinion on which transmission offers better mileage. While there is nothing wrong with that, this blog will dive into the topic to lay bare the facts, helping you make an informed decision.

The case for manual transmission

To understand how fuel economy and transmission are related, let's explore the functioning of a manual transmission (stick shift). To shift gears in a manual gearbox, you press the clutch to disengage the engine from the transmission, then manually select the gear with the gear shift, and gradually release the clutch to re-engage the gearbox and the engine. 

While this is second nature to us, it's somehow linked to fuel economy. Whether your car is petrol or diesel-powered, it has an optimum range of power, where the balance between power and efficiency is optimal. 

With a manual transmission, we use our intuition to engage gears. So, if looking for fuel-efficiency, you should shift up early and downshift later to stay within the most efficient power range.

Why manual transmission wrestled old automatic transmissions

In the past years, manual cars used to get better fuel mileage than their automatic transmission counterparts. Automatic cars have a torque converter (an equivalent of a clutch in manual transmissions), which was never 100 percent efficient when the vehicle was in motion. Power was lost when transmitted from the engine to the wheels, leading to the car burning more fuel. 

Another downside of the torque converter is that it adds weight to the vehicle compared to the clutch. And as you know, weight and inefficiency are two prime enemies of fuel economy. And as if that was not enough, older automatic transmissions had three or four gears making it challenging to stay within the optimum rev range, especially for cars with small engines. 

As a result of the above pitfalls, older transmission consumed more fuel compared to manual transmissions. That said, if fuel efficiency is a differentiator for you, look away from the old automatic transmissions. 

The case for the new generation of automatic transmissions

Modern-day automatic transmissions like GM’s 6-speed 6L90 transmission have been refined to achieve similar (perhaps even better) fuel economy to manual transmissions. Of course, technology has a hand in it, and car manufacturers are exploiting it to produce modern transmissions with the below options.

Single automated clutches

Operates similar to the manual transmission, but unlike a manual gearbox, the clutch pedal is replaced by an electronic, computer-controlled clutch. This option is lighter, becoming more fuel-efficient than the brick and mortar auto gearbox.

Dual-clutch transmission (DCT)

This works similarly to a single-automated clutch, only that it uses two clutches. The results? Seamless shifting of gears, improving the ride's quality. Because of efficiency and lightness (has no torque converter), DCTs are 3-5 percent efficient than manual transmissions and 5-10 percent efficient than traditional autos. 

Ultimately, DCTs combine the convenience of an auto and the fuel efficiency of a stick shift.

CVT gearboxes

Continuously variable transmissions (CVTs) work differently from the traditional gearbox. Instead of gears, CVTs use pulleys and a belt (chain). But how do CVTs obtain high fuel efficiency?

Apart from the obvious reasons of weight, CVTs continually alter the relationship between engine speed and power transmitted to the wheels, ensuring that at no point fuel is used much more than needed.  

This means whether running town errands or cruising on the highway, the revs remain low, saving fuel. And if you need power, the engine rotates faster without delay, unlike the traditional gearbox, which has to shift gears. While this delivers minute fuel gain, the results are more evident in the long term. 

Does the number of gears affect fuel economy? 

In case you haven't noticed, many vehicle producers are offering transmissions with seven to ten different gear ratios. This trend moves away from the norm where four, five, and six-speed gearboxes ruled the market. 

Of course, the move for additional gears is to achieve fuel economy and smooth acceleration. You see, with more gear ranges in a transmission, the gear ratio becomes small, making the throttle highly responsive, improving efficiency and acceleration. Ultimately, with high gears, you operate at optimal points, saving fuel. 

Due to these reasons, there has been a significant leap to high-gear transmissions that offer at least six gears. For instance, the 6L90 six-speed transmission built by General Motors improves fuel economy by 4 percent compared to the four-speed transmission it replaced a while ago. 

Does transmission fluid affect fuel mileage?

Transmission fluid to the gearbox is what blood is to your body. Transmission fluid plays a critical role in reducing friction between moving metal parts, especially in the 6L90 transmission. As such, switching to synthetic transmission fluid, which has smaller-sized molecules compared to ordinary oils, significantly reduces friction between moving parts.

The results? Less energy is lost, and therefore, more power is transferred to the wheels, increasing gas mileage.

The Verdict

In a world where every cent counts, fuel economy becomes pivotal when shopping for a car. While traditionally, manual cars have perennially trounced automatic transmissions in matters to do with fuel efficiency, the tables are turning with technology. Automatic cars have been refined to gain similar, if not better, fuel economy to manual transmissions.


For more information on fuel efficiency, visit here: https://www.fueleconomy.gov/feg/findacar.shtml


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About Luke Wilhoit Junior   Consultant

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Joined APSense since, February 15th, 2021, From Buffalo, NY, United States.

Created on Feb 16th 2021 15:37. Viewed 61 times.

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