# DEF, Physics question.



## E365 (Jun 10, 2013)

I always thought the theory was the opposite with fuel load. Less fuel = lighter, so less energy required to move it. But maybe steady-state is different? Either way I doubt the weight difference is enough to notice in a non-controlled environment. 

I believe a lot of truck stops have DEF pumps next to the diesel pumps, as big rigs use it too. FWIW, it seems the going rate for DEF/AdBlue is about $4.50/gallon. Usually sold in 2.5 gallon jugs for $11-$12 on sale. I'm surprised that its sold all-over now. Wal-Mart, every auto parts store, farm & fleet stores, Menards (Midwest version of Home Depot/Lowes). I stopped at a local BMW dealer to grab a little part and noticed the BMW branded DEF was $18.50, for a HALF gallon. $37/gallon.


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## tmath11 (Feb 18, 2013)

Momentum=mass x velocity. With a full tank technically your car would have more momentum. A lighter car would be opposite. But you also have to think that the more weight that is in your car the more force the tire is putting on the road so the more resistive force of friction that would be present. I would think that the pros of the momentum along with the con of the greater friction would equal out and you'd get about the same gas mileage in both cases.


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## ErikBEggs (Aug 20, 2011)

Momentum yes. Drag is the aerodynamic equations. Curb weight has a negative effect on city driving but the opposite on the highway. The aerodynamic drag is most important on the highway. That is why the Cruze with the similar gearing as the Sonic hatch (very tall overdrive gear) averages greater MPG on the highway


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## Blue Angel (Feb 18, 2011)

Just her imagination. Tell her that stopping for fuel more often will burn more fuel, and that the car will be more efficient in city traffic (speeding up and slowing down) with less fuel weight on board. That's why the Eco stops filling short of a full tank, to keep weight low and improve mileage... in the city any car will get better mileage on an empty tank, and on the highway it won't matter enough to worry about.


Sent from AutoGuide.com Free App


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## Maxzillian (Sep 16, 2012)

DEF isn't too new in the ag market. For Tier 4 Interim, AGCO (Massey Ferguson and Challenger) have been using DEF since about 2012 and Case followed shortly after. They typically consume DEF at a rate of 3 to 5% of fuel consumption so it takes a pretty big tank. 

Most guys seem to indicate they use around 2-3 gallons a day, of course the DEF consumption increases with power demand. They purchase DEF in bulk (220 gallon totes) which brings the cost down to the $3 per gallon range.

John Deere relied on cooled EGR for Tier 4i, but it looks like everyone is going to SCR (selective catalytic reduction, uses DEF) with most using cEGR as well.


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## brian v (Dec 25, 2011)

That is interesting stuff Dog . Reads like the afore mentioned sweet hearts above have figured these puzzles out for us . For the not so bright amongst the crowd . DEF = Diesel Emissions Fluid .


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## Nathan of Aus. (May 16, 2013)

Yes you have a higher momentum with a full tank which does mean that you'll maintain your speed for longer when coasting. However, it also means that you will require more energy to increase speed and to maintain it. More weight always means more fuel, that's why all the latest car platforms feature drastic weight saving measures; fuel economy.


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## Poje (Aug 2, 2012)

Lighter = Easier to move mass from start = Better fuel economy.

Thats it.


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## Nathan of Aus. (May 16, 2013)

Indeed.

Whats easier to push: a go kart or a truck? Which requires more fuel? I've done 3 years of physics and I can tell you that it's not theory; it's fact.


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## Skraeling (May 30, 2012)

Maxzillian said:


> DEF isn't too new in the ag market. For Tier 4 Interim, AGCO (Massey Ferguson and Challenger) have been using DEF since about 2012 and Case followed shortly after. They typically consume DEF at a rate of 3 to 5% of fuel consumption so it takes a pretty big tank.
> 
> Most guys seem to indicate they use around 2-3 gallons a day, of course the DEF consumption increases with power demand. They purchase DEF in bulk (220 gallon totes) which brings the cost down to the $3 per gallon range.
> 
> John Deere relied on cooled EGR for Tier 4i, but it looks like everyone is going to SCR (selective catalytic reduction, uses DEF) with most using cEGR as well.


The tractor in question i was looking at was a Massey Ferg. 8600 series if I remember. I was just surprised as her fathers tractors are older so dont have that and them being such an investment its not surprising. He was telling me about the issues people were having with the Deere's EGR and killing engines.


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## KarlZap (Jun 30, 2015)

The Cruze is all about aerodynamics. If you don't believe me drive at a steady speed (60 MPH is what I used) on a straight road on a calm day then bring down the windows one at a time and watch the MPG drop.


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## DECruzer (Jul 19, 2015)

Poje said:


> Lighter = Easier to move mass from start = Better fuel economy.
> 
> Thats it.


Probably why the ECO has no spare, a smaller fuel tank and less sophisticated rear suspension.


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## diesel (Jun 8, 2013)

KarlZap said:


> The Cruze is all about aerodynamics. If you don't believe me drive at a steady speed (60 MPH is what I used) on a straight road on a calm day then bring down the windows one at a time and watch the MPG drop.


Interesting. I figured there would be some drag, but never thought about testing it like that.


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## Kexlox (Nov 4, 2014)

There was a Mythbusters episode where they tested fuel consumption with windows down vs. AC. For the vehicles they tested, AC became more fuel efficient around 55mph.


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## pandrad61 (Jul 8, 2015)

IF you where rolling the cruze on a endless down hill slop sure heavy works better, but in the real world less heft will make the motor consume less fuel since it does not have to work as hard. I bet if you gutted the Cruze and I mean absolutely race gut it. mpg would increase drastically


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## obermd (Mar 3, 2012)

pandrad61 said:


> IF you where rolling the cruze on a endless down hill slop sure heavy works better, but in the real world less heft will make the motor consume less fuel since it does not have to work as hard. I bet if you gutted the Cruze and I mean absolutely race gut it. mpg would increase drastically


City MPG would go up. But on the open road aerodynamic drag is the determining factor. In a car, friction goes up linearly with weight and the square of the speed.


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## pandrad61 (Jul 8, 2015)

> City MPG would go up. But on the open road aerodynamic drag is the determining factor. In a car, friction goes up linearly with weight and the square of the speed


agreed. the added benefit of faster accelerating, handling, better component wear. For this you sacrifice noise cancelation, comfort, utility, and a more stable highway ride


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