Auto vs Manual MPG Question

Im always gonna drive a manual , but one thing I’m curious about is what role torque converters play in allowing ATs to get better fuel economy. Seems like some AT drivers report returning 21/25 mpg and even higher - whereas I get about 15mpg on the highway at 75 and about 18mpg at 65. 18 is the highest I’ve seen. Can automatic transmissions allow an engine to run efficiently at lower rpms thus delivering better fuel economy?

 

I believe it's more about gear ratios between the AT and MT. The AT runs about 500 less rpm at highway speeds.

 

The 4.30 Rear gear makes the manual a little lower, that said I average 20/21 so no complaints on MPGs

 

Auto 4x4 here. My lifetime best tank avg is 19.4. I can get as high as 23 on the highway under perfect conditions. I feel good with 20 mpg though.

 

I get about 17mpg city, and 20mpg highway with 6MT.

 

Put bigger tires on it to lower the ratio.

 

Ive got a 2017 trd sport automatic and i am getting highway right now with the Winter gas that is being used about 8.4km/l (24 mpg) and in town/city driving 6.5 km/l or about 18 mpg. Im running Bridgestone Blizzack snow tires atm

 

Generally speaking, autos have surpassed manuals since autos since computers took over.

www.fueleconomy.gov will show the numbers for all marquees.

Its usually just 1-2, but its there.

 

Right on. Same here after the update.

 

I still need that update on my truck, hoping it improves driveability and if MPG goes up that would just be icing on the cake.

 

I got definitely got both of those. There was a settling in period for both also. In the end, it was very much a net positive for me.

 

Same here. Average bout 18 city though

 

I’m averaging about 2 mpg better with the MT than I did with the AT. I do primarily highway driving and the MT is geared much better from my experience. If you do 90% of your driving in the city the AT is probably the way to go

 

right now with no chin strap, no tonno cover, winter gas and, running 265/70 r17 KO Bros i am at 18's to low 20's with the MT.

EDIT: stock tires, tonno, chin strap, summer gas - I was getting 22s to 24s

 

The torque converter is less efficient than a clutch due to pumping losses and fluid effects. In fact an auto transmission of the torque converter variety (not dct/dsg/smg) is inherently less efficient than a manual; however, people get confused when seeing mpg numbers and the auto showing higher. Reason being is gearing #1 and to a lesser extent, #2 computer controls prioritizing mpg over power delivery, which is the complete opposite for some reason with MTs because gearing even in 6th is designed to provide some acceleration without downshifting.

If you stick the same ratios in both transmissions and same rear end and driving both the same, you'll get higher mpgs on the MT. That said, you can regear the MT if you wish and recover some mpgs.

 

I’m manual on 35x12.5 with stock 4.3 gears and average about 15.5mpg. Best I got out of a tank with this setup is 16.9mpg. I think I was averaging about 19mpg stock. But I was only stock for less than a month.

 

The torque converter plays *no* role in improving fuel economy as compared to a manual. A torque converter plays the same role as a centrifugal clutch would. There are two shafts connected to it -- the input shaft, and the output shaft. Inside, connected to each, is an impeller. There is a drive impeller, and a driven impeller. The harder/faster the drive impeller turns, the harder the transmission fluid is driven at the driven impeller, allowing torque to be transferred to it.

Now, a newer torque converter will help improve fuel economy compared to an OLD torque converter, and this is because new torque converters (known as "locking" torque converters) are able to mechanically bind the output side to the input side, meaning that under certain conditions, the fluid is no longer the medium of power transfer. When a locking torque converter is LOCKED, it is, as far as efficiency goes, no different than a clutch that is fully engaged.

The fuel economy differences in the AT vs MT are related to the overdrive gear ratio. You see, the problem with handing a *properly geared* manual transmission to a goof, is that they shift it into overdrive, drive it up to a hill, and see the speed dropping despite being at full throttle, then they freak out thinking that its weak. Now get an automatic in the same conditions, and it will *automatically* downshift, so the goof thinks that it is stronger. The result is that the car manufacturers will intentionally UNDER GEAR the manual as a psychological manipulation toward goofs.

A correctly geared manual will be MORE efficient than an automatic.

 

Eh computers have been involved for 15+ years and no computer can overcome the efficiency losses of having a fluid coupling. The improvements have largely been because a 5-speed automatic is the defacto standard with higher gear counts being available on just about anything mid-market and above. Gear selection options and the taller final drive (that are more usable with an automatic) have greatly improved fuel economy.

You're right though... the only reason to buy an MT in the past 10 years is personal preference.

 

Just being a little pedantic, but I wouldn't use the term "new" here given that torque converter lockup was a thing in the 1950's. What has changed is that computer controls are quick enough to lock up in lower gears and not just in top-gear cruise.

A properly geared manual will be MORE efficient than an automatic except that there is not a human alive who can consistently shift accurately in all scenarios to maintain ideal fuel economy compared to a modern AT transmission. I love my MT but this is something I came to terms with a long time ago.

You also have to consider that in practice, an automatic can utilize a taller final drive without damage because it allows for slippage. It's not good for quick power delivery or towing but it's better for getting the most efficiency out of gears while not accelerating.

 

In addition to some of the 'ol favorites.
-Drive a manual, you can drive anything.

-Actually "fun" to drive.

-Still be able to be towed on pavement without the need for a flatbed, dollies or removing the drive line.

-Can be push started if the starter takes a crap.

-A more recent reason = Millennial anti theft.