Driving with fresh water tank full - is it OK?

[Skater]

Originally Posted by TG Twinkie

Based on all of this physics stuff. It would be better to travel in 100+ degree temps. Because the air is thinner and there is less wind resistance. Than at night or in cold places where it is thicker. But engines get less efficient in the high temps. So there you go! You should probably just stay home.

LOL. The engine would be more efficient at lower temperatures - denser air, and, if it's low enough that you don't need the air conditioning...

I don't "worry" about the mileage, but I do monitor it. I've been tracking it for every vehicle I've owned for at least 10 years now. All else being equal, at the end of the day, I like getting better mileage, but not to the point where I'm doing 50 MPH in a 65 MPH zone either - it's more of a "Hey, I'm doing 65 in a 65 and still getting ___ MPG!" thing. And when I'm stuck behind a slow truck while climbing a hill, my consolation thought is, "Well, at least I'm getting better mileage here."

Originally Posted by dznf0g

That is true, Skater, and more "lost in the noise" with larger displacement TVs, which are already wasting more energy than a small displacement engine simply by it's design. They are designed to be more energy efficient under load(strictly speaking from a physics efficiency standpoint, not to be confused with our colloquial use of the word).

It seems like it should be that simple, but it's not, unfortunately. In the B190 world, the ones with the 460 engine tend to be more efficient than the ones with the 351 engine, which is counter-intuitive. My theory is that the 460 doesn't have to work as hard to move the van, so in the end it burns less fuel, despite being larger.

[dznf0g]

Originally Posted by Skater

LOL. The engine would be more efficient at lower temperatures - denser air, and, if it's low enough that you don't need the air conditioning...

I don't "worry" about the mileage, but I do monitor it. I've been tracking it for every vehicle I've owned for at least 10 years now. All else being equal, at the end of the day, I like getting better mileage, but not to the point where I'm doing 50 MPH in a 65 MPH zone either - it's more of a "Hey, I'm doing 65 in a 65 and still getting ___ MPG!" thing. And when I'm stuck behind a slow truck while climbing a hill, my consolation thought is, "Well, at least I'm getting better mileage here."



It seems like it should be that simple, but it's not, unfortunately. In the B190 world, the ones with the 460 engine tend to be more efficient than the ones with the 351 engine, which is counter-intuitive. My theory is that the 460 doesn't have to work as hard to move the van, so in the end it burns less fuel, despite being larger.

That is exactly what I mean. With the bigger engines, which are designed and cammed...etc. for loads, there is much more wasted energy (fuel) while empty and less of an impact on economy as load is applied. They are more efficient at hauling a load than they are efficient at no load. Don't misunderstand me, mileage will still decrease with incremental loading. That is not the usage of the word efficient I am talking about.

Let me explain it this way: Remember the folks with a big block 454 Suburban who say, "I get 9mpg whether towing my 34'er or empty"? That's what I mean...the truck was built to haul and load had little impact on mileage since there is so much "waste" energy between what it takes to move the empty truck and less "waste" energy left on the table when loaded. The same statement cannot be made for a smaller vehicle (or engine) whose primary build purpose was not to haul heavy loads.

In the end, OP does not list his TV in his profile. He has a 20' AS. If he is towing with a Corolla, 240# extra weight on top of his gear and ammenities could make a SIGNFICANT difference in mileage and safety.......If he is towing with a 1500 truck, go for it...heck put some extra water in jugs in the bed and boondock longer.

[Jim Flower]

Originally Posted by polarlyse

Yes, the math IS the math. If you calculate using a calculator to many decimal places you may think that the water weight is impacting your mileage. If you do the math using a slide rule much less so. When traveling the water is optional until you need it. I always travel with at least 1/2 tank. Sometimes a full one. You never know when you'll need it.

Chuckle,chuckle. I think this audience actually knows what a slide rule is. Me, full water, empty holding. Don't care about the cost. Investing a small fortune to drag around a fancy port a potty and then not have water to do a decent flush doesn't make much sense.

[TouringDan]

dznf0g is correct. It takes more fuel to haul extra weight. As we all know, there is no free lunch. I think the big argument is that the experience with most folks is that towing the extra weight does not seem to require extra fuel. It is so small that it can not be measured. For example, my truck and trailer weigh about 12,000 lbs. If I carry just a little water in my 40 gal tank, I weigh about 300 lbs less. Assuming the 10%/6.5% GM number is correct, my fuel economy will go up by 1.5% from 13.5 to 13.7 mpg. This is not measurable and would never be a reason to not carry water IMHO.

One way to understand the statement that carrying extra weight requires extra fuel and more energy is to look at the simple exercise of moving a wheel barrel. It is quite easy to move a wheel barrel empty. Now fill it with concrete and see how much harder it is to move. It takes quite a bit more energy to move a wheel barrel with 400 lbs of concrete in it than an empty 40 lb wheel barrel.

Dan

[Kosm1o]

I've been thinking about my earlier post in which I explained , to my surprise, that I get better mileage by 1 to 2 mpg with my 6500 - 6800# 28' Safari then I got with my ultralight 18' box tt weighing about 2800#.
I think the only way to explain this is that after a certain speed, wind resistance trumps weight. This is where a graph would be really helpful. Unscientific Conclusion: if you are going to travel at 60 + mph, that extra weight does nothing to hurt mileage.

[MaxTow]

We're really beating this one to death - but I cannot resist.

Caution raised on overarching statements - this holds true when saying all weight impacts fuel economy. Again - not necessarily. It depends on the type of driving.

All those who have cited examples of better mileage pulling airstreams versus square trailers - this is due to the better drag coefficient. Less wind resistance. If one was pulling the two trailers in stop and go traffic for many miles, the SOB combination would likely have better mileage.

So not all weight is detrimental to mileage. This is why trucking companies add fairings to their rigs. It's more weight - but it reduces the overall cost of hauling.

And if we were so worried about mileage and pulling the extra weight of the water, we'd also recommend never starting off with more than 1/2 tank of fuel. It's the same argument. Why don't we? Convenience.

[dznf0g]

Originally Posted by MaxTow

We're really beating this one to death - but I cannot resist.

Caution raised on overarching statements - this holds true when saying all weight impacts fuel economy. Again - not necessarily. It depends on the type of driving.

All those who have cited examples of better mileage pulling airstreams versus square trailers - this is due to the better drag coefficient. Less wind resistance. If one was pulling the two trailers in stop and go traffic for many miles, the SOB combination would likely have better mileage.

So not all weight is detrimental to mileage. This is why trucking companies add fairings to their rigs. It's more weight - but it reduces the overall cost of hauling.

And if we were so worried about mileage and pulling the extra weight of the water, we'd also recommend never starting off with more than 1/2 tank of fuel. It's the same argument. Why don't we? Convenience.

Drag coefficient and weight penalties are two completely separate calculations, as is driveline friction and rolling resistance. NO weight can be moved on this planet without energy input to get it moving, keep it moving (less), and stopping it (heat in brakes, which cost fuel as well) This is high school physics folks.

[tosten]

You are right..physics can't lie. Here's another for you. What is the breaking point where carrying the weight of the a large volume of fuel overwhelms the cost of slowing and accelerating for an extra fuel stop? I've thought of this with the 40 gallon tank on my old Suburban.

[mandolindave]

What I don't like to do is tow with the tank half full. I could feel the weight of the water sloshing around. Then someone posted that their tank cracked while driving. So if I am going somewhere where I will have hook ups or access to water, I travel empty. I always carry water in a container for use on the road, and to use to transport water while camping without hookups.
Andy is right though, I never thought about the center of gravity aspect.

[featherbedder]

Since 1962 I have always traveled with A.S. water tanks full. I pur. 1976 new still go with full tank of water w/no prob. Also never dump while camping except when ext. stay.

[Bill M.]

My rig weighs about 13000 lbs. Is 200 lbs of water really going to make much of a difference? I like having water and fuel in my tanks when I travel.

[AldeanFan]

You can't argue that adding more weight or making the less aerodynamic doesn't require more energy (fuel) to travel.

However, the amount of additional fuel may not be significant.

For my rig, I get about 400km to a tank of fuel towing at 65mph on the highway.

Trailer mostly empty, truck mostly empty, no water = 400km

Trailer packed for dry camping, full water, 2 Generators, 2 extra gas cans, large tool box, = 400km

Full water, canoe on the truck = 400km

The 4.7L Toyota doesn't seem to care what I bring or how I load, as soon as I hook up the Airstream it's 400km till empty.

When pulling the 1500 pound, 13 foot Fiberglass Trillium trailer we get about 450km to a tank. Funny how pulling a trailer twice as long and 2 1/2 times as heavy has so little effect on fuel mileage.

FYI, the truck gets 550km to a tank empty.

[loudruff]

And don't forget to throw in a water filter. We carry a filter in case we have to replenish the water supply while we are out traveling. We have come across places that have "well" water that looked ok, but was brownish when put into a glass. Ugh! We always filter in places other than home.