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Old 02-04-2015, 06:57 PM   #1 (permalink)
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4x4 fuel drain, solutions?

Winter here is just getting to its "fun" part (you know, the slush, freezing rain, ice, all dat snow stuffs) I'm occasionally using 4x4 on the drive home. Now I have noticed this, combined with OD lockout drains fuel about 2 mpg more than normal. Does anyone have an idea to minimize the effects of 4x4 use? I was thinking of getting manual locking hubs for better weather so the drive train in the front doesn't get dragged along by the wheels on turns.

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Old 02-05-2015, 07:47 AM   #2 (permalink)
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Am I interpreting correctly that your truck will not let you go into overdrive in 4x4, or are you choosing not to go into overdrive in 4x4? Unless there is some truck specific issue not to, I would still use overdrive in 4x4 if possible, assuming you are traveling fast enough that it is necessary. My Chevy automatics had no problems in 4x4 and overdrive at the same time. My Chevy/Toyota stick shifts didn’t really have much of a say in the matter and did fine in 4x4 and Overdrive.

Are you using instant feedback (gauge or other) to determine the 2MPG loss, or is this a tank average?

If it is an instant loss, are all your tires the same brand and size? Running differently sized tires puts a lot of strain on a typical transfer case, which has no differential forcing the front and rear axles to spin the same RPM. Small differences in tire diameter will forcibly make one wheel slip after it builds up sufficient strain on the gears/belt in the transfer case.

If it is a tank average, note that it is typical to get lower FE in super cold weather, in rain, or driving through slush/snow so it may not be a 4x4 issue, just a weather issue.
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Old 02-05-2015, 08:00 AM   #3 (permalink)
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Manual locking hubs will get you better non-4x4 FE and will show a bigger hit when using it. Some systems keep the trans out of OD while 4x4 is engaged under the assumption that if you need all 4 turning, you probably shouldn't be driving 70mph. Some trucks also suffer bad handling characteristics while in 4wd at higher speeds so keepng trans out of OD kinda keeps the driver out of that bad zone.

Keep in mind that with manual locking hubs, it is recommended to periodically lock them to make everything turn and distribute oil to keep bearings and stuff from going dry.
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Old 02-05-2015, 08:58 AM   #4 (permalink)
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A 2mph hit in economy is about what one would expect with 4wd and OD locked out.

Why are you locking OD out when in 4wd? I do no think the Dodge Ram does that as a default, is it to keep the motor from lugging?

Manual locking hubs will net you a slight increase in fuel economy when the weather is nice and you do not need 4wd. It will not change a thing come winter time when you are in 4wd. If they make replacement hubs for your Dodge, I would get them..

On a side note. My Silverado does not have an aftermarket manual locking hub available. What I do when traveling long distances "when I haul the 5th wheel down to Florida for vacation" is to pull the front axles out. To do this, you need an old pair of axles so you can disassemble the axle and keep only the outer half shaft. then you install that only into the truck "essentially making it a 2wd". I have logs showing a 1.5mpg increase while towing doing this mod.
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Old 02-05-2015, 10:56 AM   #5 (permalink)
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Quote:
Originally Posted by aardvarcus View Post
Am I interpreting correctly that your truck will not let you go into overdrive in 4x4, or are you choosing not to go into overdrive in 4x4? Unless there is some truck specific issue not to, I would still use overdrive in 4x4 if possible, assuming you are traveling fast enough that it is necessary. My Chevy automatics had no problems in 4x4 and overdrive at the same time. My Chevy/Toyota stick shifts didn’t really have much of a say in the matter and did fine in 4x4 and Overdrive.

Are you using instant feedback (gauge or other) to determine the 2MPG loss, or is this a tank average?

If it is an instant loss, are all your tires the same brand and size? Running differently sized tires puts a lot of strain on a typical transfer case, which has no differential forcing the front and rear axles to spin the same RPM. Small differences in tire diameter will forcibly make one wheel slip after it builds up sufficient strain on the gears/belt in the transfer case.

If it is a tank average, note that it is typical to get lower FE in super cold weather, in rain, or driving through slush/snow so it may not be a 4x4 issue, just a weather issue.
The area I drive in is very hilly so I manually lock out the OD, all tires are identical and I use the in car computer to determine what instant MPG I get and I also track each trip and so far its like 2 mpg less on the same route opposed to 2WD
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Old 02-05-2015, 02:19 PM   #6 (permalink)
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So you always lock out the OD when you travel this route, both in 2wd and 4wd? If so that shouldn’t make any difference between the two data sets. If you only lock it out in 4wd that is probably part of the MPG difference right there.

Assuming you always lock it out of overdrive in 2wd or 4wd, since you don’t have manual locking hubs, your front axles and CV joints will be spinning all the time anyway, so those wouldn’t make a difference between the two data sets.

The only difference should be the front differential would be engaged by the actuator and your transfer case should shift. This would result in your front drive shaft spinning, front differential being engaged and spinning, transfer case chain engaged and spinning, and meaningful power being transmitted to the road by these components.

From my experience with 4x4 trucks, with everything in working order I would not expect to see a 2 MPG or approximately 20% drop from solely this difference. Either the other factors (weather, road conditions) are causing some or all of the drop, or something isn’t functioning correctly.

Have you checked or changed the fluid in your differential and transfer case recently? In super cold weather my truck feels very “sluggish” when I am coasting until the transmission, transfer case, and both differentials get warmed up a bit.
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Old 02-05-2015, 07:44 PM   #7 (permalink)
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Quote:
Originally Posted by aardvarcus View Post
So you always lock out the OD when you travel this route, both in 2wd and 4wd? If so that shouldn’t make any difference between the two data sets. If you only lock it out in 4wd that is probably part of the MPG difference right there.

Assuming you always lock it out of overdrive in 2wd or 4wd, since you don’t have manual locking hubs, your front axles and CV joints will be spinning all the time anyway, so those wouldn’t make a difference between the two data sets.

The only difference should be the front differential would be engaged by the actuator and your transfer case should shift. This would result in your front drive shaft spinning, front differential being engaged and spinning, transfer case chain engaged and spinning, and meaningful power being transmitted to the road by these components.

From my experience with 4x4 trucks, with everything in working order I would not expect to see a 2 MPG or approximately 20% drop from solely this difference. Either the other factors (weather, road conditions) are causing some or all of the drop, or something isn’t functioning correctly.

Have you checked or changed the fluid in your differential and transfer case recently? In super cold weather my truck feels very “sluggish” when I am coasting until the transmission, transfer case, and both differentials get warmed up a bit.
As far as maintenance my truck runs full synthetic for all fluids and with the exception of my transmission and PS loop (have to use mopar fluid) the brand used is royal purple. My truck is parked in a 50ish degree garage so I would assume temps would start around there when I go to drive somewhere. I seriously doubt it can be any mechanical problem but heck, it might be. Ill do the route tomorrow in 4x2 there and 4x4 back with the OD on and report what happens.
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Old 02-07-2015, 12:38 AM   #8 (permalink)
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Okay so after the trip to work and back I found the difference to be 1.2 mpg. I also noticed the truck always revs higher for any given speed than in 4x2

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