Auto vs. Man. efficiancy

[R.M.THOMPSON]

One question that seems to come up now and again is transmission efficiency , as a general rule manuals are better for fuel millage. I'm not trying to start a discussion on what trans is better,just the fact of, if both transmission's were placed in 1:1 ratios. . ie,(5600 in 5th & 48re overdrive locked out). What would the fuel millage differences be at a steady state? I think 3. 73 gears with 265 tires would be about 1700 rpm's @ 50 mph.

Mark T.

 

[Prairie Dog]

In the scenario you describe I don't think there would be any real difference between the two - but you'll never drive like that so it's best just to get what suits your needs. Lots of stop and go ? Get an auto. Mostly towing heavy? You won't be disappointed with a 6 speed.



Scotty

 

[NIsaacs]

R. M. THOMPSON,



Based on your comparison, with empty trucks the fuel milage would be about the same. I am not very knowledgeable on the newer autos, so I will try to be careful here. As a general rule, a stock auto will not put the power to the ground like a standard will. Autos like high RPM to be efficient. The fuel milage will suffer on the auto when the converter is sliping, as in accelerating from a dead stop or pulling a hill with a load. Dodge has improved on this issue by raising the RPM and widening the power band. They started out with 2500 rpm engines with poor performance. The 5. 9 Cummins in Bus, Motorhome, and Fire trucks has a higher HP level than in medium duty trucks. This is because they all use automatic transmissions and can't "lug" the engine like the medium duty truck with a standard trans. will. The Dodge has a lot higher HP level than all other big rigs, but get by with their lower GCW restriction. To answer your original question, the auto will normally get less fuel milage because of the torque converter slipage.



"IF IT AIN'T CUMMINS POWERED, IT AIN'T A TRUCK"



"NICK"

 

[Snow man]

the fuel milegae difference locked up 1 to 1 would be very little. At that point the only thing extra your turning in the auto is the front pump. So whatever HP the pump is robbing to build line pressure is about it,the internals are locked together at 1 to 1,and I would think the diff in mileage would be so small you couldnt accuratley measure it, i bet the pump doesnt even draw a 1/2 hp at cruising rpm and pressure.

 

[DocDetonancour]

I agree that mpg is a non issue with the auto vs the manual. I currently have the auto and can pull 23+ in the scenario you described. I would have to believe that those that get poor mileage is for some other reason than the trans. IMO Doc

 

[klenger]

All that heat from the automatic transmission's cooler has to come from somewhere.

 

[Snow man]

the heat from the autos cooler is no more than the heat given off by the trans case of a 6 speed when in lockup. In fact when in lockup ,most of the heat is pumped into the trans from the engine mounted cooler, it heats the fluid before the front mounted cooler takes it away. This is to keep the trans from running too cold in northern regions. I removed the engine mounted cooler and in lockup on a 70 degree day my trans temps run 95-=110 degrees in the pan towing 9000lbs in OD locked up. Last yr i towed the same trailer on the same route at the speeds and it ran 160 degrees, the only difference is the engine mounted cooler is removed. A standard would be running close to 200 degrees easy towing this weight at these speeds . If you took all the coolers off the auto and looped the line i bet it would run within a few degrees of what a standard runs with both in lockup.

 

[R.M.THOMPSON]

Thats a good observation KLENGER, I wonder how much heat is transfered back into the trans fluid from the engine mounted cooler(very little at cruising speed),and also , is that a reason that tran temps seem to stop climbing at such a rate when 200 degrees is approached ? Prarie Dog , the only dislike that I have for the 48re is the O. D. rpm drop when shifting at medium acceleration or in another sense feathering thru at little to zero rpm drop & using enough throttle to hold out the shift to about 2500 rpm's to stay in the power band. The problem I have currently is most of my 27,000 miles is at about 45 to 60 mph with a lot of variation. (loaded and unloaded) What a poor reason on my part to stay away from a auto on the next truck. That is some of the reason for these questions , as I need to up the payload capacity and box lenth without losing passenger room that a Quad Cab gives I thought with careful selection of gearing with 315 tires the 1700 rpm sweet spot can cover center of my MPH range without using Overdrive as a main use gear. I suppose the question to end in would be, Does anyone have first hand experiance in setting up a transmission to hold out O. D. without playing with the O. D. or tow haul button, until about 65 mph(2250 rpm - 500 for the shift = 1750)???????

Appreciate the help fella's as I'm not trading this truck for the feel good stuff and eye candy , just the working ability !

Mark T.

 

[RTuvell]

In my mind "transmission efficiency" is one thing when it comes to "engineers" and its another thing when it comes to "drivers/owners". As an owner/driver the transmission efficeincy that matters most to me is overall MPG. IMHO the manual transmission gives the driver "the ability" to achieve the best overall efficiency (MPG), but it is up to the driver.



The extent to which the transmission can impact MPG can be a matter for the manual transmission driver to determine via his driving style whereas the automatic driver has much less control. The manual driver can vary shift points and cruising rpms searching for the best MPG. The manual driver can get into higher gears (better MPG gears) whenever he chooses. The manual driver can frequently "coast" up to stop lights and in other appropriate situations. Someone else first mentioned the "coasting" ability of these trucks then I tried it and I was amazed.

 

[Briman]

Pull a heavy trailer up a steep hill and see how good that cooler works... I'll bet you'l find that your coolant temp gauge will peg in short order... On the other hand, I got better mileage with the auto than other manuals I've had, go figure.

 

[Snow man]

The coolant temps will rise equally on auto and manual trucks provided the trans is in lockup,which mine always is. i never ever drop out of lockup or OD to pull a hill unless im forced to slow down,then its to 3rd locked. Autos will get better highway mileage,due to the OD ratio or . 69 to 1 it allows the engine to turn slower and get better mileage than the 5/6 speeds.

 

[Briman]

If you pull a steep hill with a load at a SLOW speed the heat rise is not equal. The auto will over heat in short order. At highway speeds the heat rise is similar.

 

[Snow man]

The heat rise is the same as long as the auto is in lockup. I can be locked in any forward gear,and it isnt going to matter. the only time the heat rise is faster in when the auto is in fluid coupling,and a stock truck with stock power is usually in fluid coupling on big hills,since it cant hold the road speed needed to stay locked up[ in 3rd. Since 03 even the stock 48Res will lock in 2nd now. The aftermarket has been moddding vbs to keep them locked for ex brakes,and racing for yrs.

 

[John - K5AWO]

Originally posted by RTuvell

The manual driver can frequently "coast" up to stop lights and in other appropriate situations.

An auto transmission will "coast" also. I do it all the time to keep the RPMs up to 1100-1200 so the A/C will put out fridig 40* air for the wife AND to help improve on the MPG in town. I frequently shift into neutral after dropping below 30 mph.



The difference in coasting distance between my auto in neutral is not all that much different than what my manual transmission did in neutral.



The stock torque convertor on my 98 24V is almost as good as a clutch held out. The fluid coupling is so damn poor below 2000 RPM.

 

[nickleinonen]

The manual driver can frequently "coast" up to stop lights and in other appropriate situations

i rarely ever coast in neutral with my truck when coming up to a red or a stop. i'll downshift through the gears until 3rd, then let it coast in gear until i need to stop...

 

[John - K5AWO]

I'm old school. I kicked it in neutral, and released the clutch to take the pressure off of the throw out bearing so it would last longer.



I know the safety factor of needing to have a fast shot of power. I would make a subjective judgement on that as to whether it was safe to put the manual transmission in neutral.

 

[y-knot]

That kicking it into neutral, at stops makes it alittle hard on the brakes dosn't it??

Also don't forget that the Automatics make 40% more torque while the TC is unlocked. That gives you 40% or 240lb/ft more lb/ft of torque on take offs and around town on a new 600 then the guy's with a manual trany. Just one of the reasons the auto's are faster and pull nicer. The Dodge auto isn't much in stock form, the TC has to high of a stall, and not enough cluth or pressure for lock-up. Up-grading to an aftermarket set-up helps, and will allow the trany to live in condittions that would injure or cause failure to a stock auto. Heat is always an issue, auto or manual, engine or rear end, it is the by-product of friction. When a TC is not locked-up, it generates heat, when it is un-locked and under a heavy load it generates a huge amount of heat, but that amount is nothing compared to the heat a TC generates while slipping, or a manual slipping. The engine mounted cooler is there to bring the auto fluid to a minimun temp, this warming maintains go flow and allows the trany to work and shift with some consistancy. Any excessive heat will be removed by the front mounted cooler. My trany seems to like the 150 range, before I went to ATS, it stayed in the 170 range, and would shoot up very quickly in traffic to 200-210, all of this towing. Under no load as in running empty, it stayed 160-170. We just came back from a 1100 mile trip and according to the CAT scales we were at 22,560lbs, the ATS never went over 170, most time staying in the 150 range, quite an improvement.

 

[John - K5AWO]

Kicking it into neutral...

That kicking it into neutral, at stops makes it alittle hard on the brakes dosn't it??



Ummm, I think that there is a great discrepancy in the way I drive and the way your comment makes me think you may be driving.



When I put the transmission in neutral, it is at a distance that the truck will coast to where I want to stop. I rarely have to use brakes above 10-15 mph.



I drive the same nearly all the time. Judging distance for coasting from 40-45 is quite easy with a little practice.



For instance, I watch the street lights a mile in advance. I pace them to always make the green. If one of them triggers red and I am just crossing the 1/2 mile intersection, I kick it out of gear and just coast making the next light on green.



Traffic goes around me and guns it right up to the light, then screeching tires when they "have to stop". I just cannot fathom folks driving right into a red light, but they do it all the time.