Auto vs Manual MPG Question

'fluid coupling' efficiency losses are largely mute - most/all current modern ATs have lockup converters that are locked during highway/cruise were any potential fluid coupling efficiency loss is muted/insignificant. And at lower speed stop&go etc, then driving style will far over-shadow any MT/AT efficiency differences. So, agree any reason MT verses AT is personal preference/choice/need.

 

I'm speaking toward efficiency losses during acceleration and around town. At cruise at any speed, it makes no difference because a new AT will lock up in 2nd if you aren't varying the throttle much.

When it comes to highway cruise, it's always just been a matter of gear ratios because cars have had lockup since the 50's and it was common in the 60's onward. MT vehicles were more efficient because they had more gears and could more easily implement a taller OD gear. Now that AT vehicles have caught up in that regard, the MT is basically just for enthusiasts.

 

AT are still restricted to a certain number of pre-selected gear ratios. No computer controlling shifting can choose between gears. Slipping doesn't accomplish anything useful EXCEPT while accelerating (because that's the only way it can change gears without exploding). Slipping wastes energy. No MT wastes energy while shifting as EVERY AT does.

 

Here’s my take-

1. If the MT had a taller OD our highway MPG wouldn’t be so bad.

2. Driver will never be as consistent and accurate at selecting the best gear for optimal MPG at every single second. This plays a big role in stop and go or around town.

When I had the auto, I could barely feather the gas and get crazy MPGs without any drama, rattling, shaking etc. Manual is my personal preference, but I’ll be the first to say it’s not better on MPGs than the auto offering.

 

The one I made bold is not usually true. The reason is because the manual transmission will typically be splash lubricated, and it will be the COUNTERSHAFT that dips into the oil to splash, but if the input shaft is stationary (which it will be any time the clutch is engaged and engine is off), so is the countershaft.

Now that doesn't mean that moderate towing without torque on it will cause it to blow up. After all, some oil will stick to the bearings for quite a while.

 

An MT itself doesn't waste energy but the driver does. You will not shift as efficiently as a properly programmed AT.

Slipping on start allows for taller gear ratios and tighter gear combinations that increase efficiency. With an MT, there is a certain speed you must be traveling where you don't bog the engine - until you reach that point you are wearing the clutch. An AT doesn't have that issue and can therefore be in that zone longer without damaging components.

Also, CVT and dual-clutch automatics exist and do exactly what you say an AT can't do. The CVT can have literally any ratio it wants within its range and the dual clutch will operate as efficiently as a manual with the benefits of an AT.

 

You make the mistake of assuming that a shift has to be "efficient". There is, in fact, nothing wrong with coasting for a while with the clutch pushed in.
The place where efficient shifting comes into play isn't in fuel efficiency, but in maximizing performance in racing, and that is a totally different subject.

 

What mistake? Shifting too early or too late will have a massive impact on your stop and go fuel economy - you act like there's only one definition of efficient or something.

Also, coasting isn't exclusive to a manual transmission. Most modern automatics will default to a higher gear and cut fuel while coasting so it's actually more efficient than an MT which will still be maintaining idle.

 

Actually, AT's are MUCH MORE sensitive to the "slip" region than MT's are. With an MT, you can control the engagement through to complete lockup with negligible heat and wear. But with an AT, they're generating huge amounts of heat any time you load them without the torque converter being locked. Haven't you ever wondered why MT's don't need additional transmission coolers to work hard? Someone who is skilled at manual transmissions can run them for hundreds of thousands of miles before wearing the clutch out, even with continual heavy towing.

We aren't talking about CVT's, which have their own problems when you start loading them up. Ever seen a dumptruck with a CVT?

 

Uhm... nope.

Didn't say it was exclusive to MT, and whether it is or is not is entirely besides the point.

 

Yup, we're done here. Not getting into a pissing match with someone who (yet again) cherrypicks massive extremes to make their point.

 

You brought it up.

 

28mpg is my best so far, with 265/70/17 BFG Ko2. Worst is 14.5mpg.

It’s all about being light on acceleration and keeping a those RPMs low.

 

I average 14.3 with my manual in the city. And about 17.5 highway. I’m not trying to get more effeciency, in fact I couldn’t care less. It’s worth $4-6 extra a tank to have more fun and drive with the pedal down.

For comparison I averaged 11.9MPG city on my 2nd gen auto and 13.4 highway over 6 years.

 

I’m 10-14 city and 15-18 on highway. I think it must be because I’m keeping the engine at 2500-2900, instead of lower at 1800-2000 where the auto transmissions seem to like to keep it.

 

Also a service technician driving deterrent

 

16mpg here consistent.

Manual transmission.

This is on 285' @ 40psi, 17" wheels, lifted 3"
I drive it normally..not thinking about light pedalling etc etc...just enjoy it as I have every other vehicle.

It is what it is

 

Modern automatic transmissions usually outperform their manual counterparts. Both in economy and often performance.

 

No, automatic transmissions outperform the OPERATOR of a manual transmission.
Manual transmissions, by themselves, are more efficient than automatics but only with the human element removed and really, it's within a few percent.

 

17.5-19 mpg on most tanks with a 2" lift, duratracs, rtt, and prinsu rack.

I just got the manual because I enjoy driving it more, to sum it up short.