# Water tanks.-Travel with full or empty tanks?



## autostratus (May 9, 2005)

GeorgeTelford said:


> Hi Gerhard
> ..................
> Like you all systems will be primed before leaving on a long journey would only had a small amount of water, probably better on fuel econonmy to get the water on or near arrival.
> .................
> George


George I've taken this from another thread as I think it raises an interesting point and worth discussing as a seperate issue.

I've read before that motorhomers think that not carrying much water will reduce their fuel consumption.

Is there any evidence of this, bearing in mind that for most of us we are likely to be reducing the weight by only 60, 70 or possibly 100kg in a gross weight of around 3500kg, around 2.5 to 3 percent. It could be that any perceived saving is the result of a following wind.

We keep our tank topped up as we often don't know how convenient (or clean) the next water point will be.

We only reduce the amount of water we carry when we think that we may be somewhere near our maximum permitted gross weight or we are on our way home.


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## peejay (May 10, 2005)

Hi Gillian,

With a relatively small (80ltrs) tank, i don't think travelling full makes much difference to our fuel consumption and even if it did its a small price to pay for the convenience when you arrive at the other end, if, like us you go away spontaneously and are never quite sure where you'll end up, you never know whether water is easily available or can trust the source, better to have some with you. Incidentaly our fuel consumption averages about 30mpg with an 'always full' tank so more than happy with that and it's not even 'run in' yet.

Incidentaly, the one and only time we run with a 1/4 tank is like yourself, for the return ferry trip and journey home from europe, it then gives us more payload for extra cheap plonk (sorry, quality red)!

pete.


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## 88838 (May 9, 2005)

Hi Gillian,
we have always kept water at about 1/3 for travelling, probably doesn't make that much difference in the scheme of things but we generally use camp sites, always carry bottled water 'cos I don't like the taste of the stuff from the tank. 
Since we got this van which doesn't have a water heater [no shower therefore you won't need hot water said the man??- he obviously doesn't do the washing up!] we rarely bother with the tank at all, just use waste.
We generally only fill fuel tank about 2/3rds full as well.
:dontknow:

In your case makes more sense to travel as you do, besides as a proportion to your van weight it's negligible - we probaly go at about 2.5kg if that.

8)


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## Boff (May 10, 2005)

Hi!

Some facts:

1. For an average van (like mine... :wink: ) of 3.5 tons max. allowed gross weight filling in or not filling in of, let's say 100 litres of water makes a difference in weight of about 3%.

2. When travelling at "normal cruising speed" (let's say 100 kph) about 80% to 90% of the engine's output is used to overcome the air resistance.

3. When travelling at constant speed on a level road the additional mass of the water makes (besides a very small effect on mechanical friction) _no contribution at all_ to the fuel consumption.

4. Only in two situations has the additional mass any effect on the fuel consumption: When you accelerate and when you go uphill.

Keeping this in mind we can define a kind of "worst-case-scenario": Going constantly uphill at extremely low speed (so that air resistance can be neglegted). In this scenario we will have an increase in fuel consumption in proportion to the mass increase, so about 3%.

So under almost all normal driving conditions the increase in fuel consumption will be far less than 3%. Except maybe along the Norwegian fjord coast, where you can go from sea level up to a 1000 metres and down again several times a day.

My consequence: Except when we know exactly where I will arrive in the evening *and* I know for sure that water supply is no problem there we start with a partially filled tank. Just enough for lunch, dishwashing and the occasional loo session. So, as we are also quit spontaneous, almost never.

Best Regards,
Gerhard


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## Andysam (May 10, 2005)

No question for me. I have a very small tank and mostly wildcamp, but shower every day, so it's a full tank and top up whenever possible.


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## 88724 (May 9, 2005)

For piddly tanks forget it but bear this in mind

Here it says for each 50kg (50 litres) = 2% worse economy
Here

Metric Horsepower 736 watts or the energy needed to move 75kg (Just over the weight of a fiamma water tank) at 1 metre per second 
(2.23 MPH)

Depending on your tank size lets say 150 Litres on a vehicle that does say 24 MPG on a 300 mile trip this costs and extra £3 in fuel so The cost for baby Tanks is not massiveif you Drive carefully, it will be higher If you drive a larger motorhome (higher drag) at higher speeds

Yes a high proportion is getting over drag but weight does still figure in getting up to speed and maintaining it.

Unless it was going to be a problem finding water traveling with 75 Litres is neither here nor their I think its when we talk good size tanks that it would be a bigger concern (300 Litres (KG) and above)

George

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## 88847 (May 9, 2005)

*cost v water*

i am with what andy and george say

but

if my wife had no water to shower, wash dishes, etc, then my life would be hell, so i guess i will carry all the water possible

Paul


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## hymmi (May 9, 2005)

This is interesting Gillian,my husband is always on about water weight and his batteries,he does my head in,thanks George, will make him read this.

We travel with enough to get a shower in morning and then fill up at large garage where you know water is from mains,although we don't drink it.Then dump it on way home.

RedOne you are learning fast. :lol: :lol: :lol:


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## Boff (May 10, 2005)

GeorgeTelford said:


> Here it says for each 50kg (50 litres) = 2% worse economy
> Here


Yep, but that is calculated for ordinary passenger cars. Given that the average motorhome has about three times the mass of such an ordinary car, the _relative_ increase in mass is about one-third.

And an ordinary car has _much_ lower aerodynamic drag than a motorhome, thus making the effect of additional weight much more prominent.

So I still stand to my conclusion: If you don't drive too much up- and downhill and keep a fairly constant cruising speed ("their" tip no. 3...) and don't have an "oversized" water tank, you can neglect the effect on fuel consumption.

Best Regards,
Gerhard


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## 88724 (May 9, 2005)

Hi Gerhard

Thats a little too simplistic, I know there is a vast difference between getting something moving and keeping it moving, but in reality unless you are cruising the flatter sections of Route 66 with no other traffic, then the slow down speed up nature of motoring means we are forever excelerating and descelerating that extra MASS.

In a sub 3.5 Tonne van over hundreds of miles the usual small tank is not going to impact much £3 max if you drive really badly tail gate stop strt charlie.

3.5 Tonne to 7.5 Tonne unit no the the econonmy of these vehicles is lower due to size and weight and larger engines anyway so with middling tank this a couple of percentage points makes a much bigger difference.

To give you an idea a 7.5 Tonne lorry will give BETTER fuel economy than a weighed down 3.5 tonne Iveco on long European motorway hauls , but if the Lorry as a big filled water Tank it will use more fuel Especially on UK Motorways.

On A and B roads it will be even worse due to accelerating the load over and over then you will be wasting some serious cash.

Americans over here and over there dont usually gove a monkies.

George


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## phylymann (May 9, 2005)

Everyone is talking about weight and economy, where as I would be more worried about stability.

All that water sloshing about in a full tank,half filled tank or almost empty tank.

Any thoughts :!:


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## 88847 (May 9, 2005)

phylymann

My tank has baffles moulded in the plastic(from the top), 120 ltrs, never heard it slosh yet, and we have had it at all levels

Paul


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## 89146 (May 15, 2005)

I drive in the naive belief that full tanks so low down help to stick the beast to the road a bit better in windy conditions. So..... full water tank plus only empty the waste when I have to. :lol: 
Plus I like to arrive at the end of a long journey not having to mess about getting water - i'm usually ready for a cup of tea and bed!

Gill


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## 91929 (May 1, 2005)

*Empty or full water tanks*

Having worked with a motor cycle racer who worked out the amount of fuel to carry round the IOM circuit to the last 1/4 pint in so many 'x' laps and that he also had to take into account the weather & barometric pressure (so he said)

He was talking of travelling at max (he hoped) speed

Then recon up the speed of a MH & the fuel consumption (we get 34 mpg overall) 
The fact that we may not always find a campsite for the night (or get stuck on the Mway for accident or SNOW)
We carry a full 100 ltr tank + full toilet flush - & - EMPTY waste water & toilet cassett.
EXCEPT in V Cold weather when we just carry some 2ltr plastic bottles inside (these have a foul taste The tank is better)

When we towed a _caravan _ we used to carry a 6 gall aqaroll & 2 gall plastic container for the same reasons

At least last time we were held up for 4 days to cross the border into Spain we could have warm drinks & food


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## Anonymous (Nov 10, 2000)

Well I think I will take all this "on board" & commence filling up my water tank before leaving home. It's a 90 litre tank & the MAW is 3,100 kgs. It only does about 25 mpg anyway so if it costs me a couple of quid it will be well worth it to avoid the problems I have had when arriving at sites. 

Four times we have parked up, unwound the Omnistor & pegged & guyed it & pitched the windbreak, unloaded all the chairs, table, barbecue, spare gas bottle, fire bucket etc then remembered we need water.  

On a number of occasions we have not had the correct connector for the tap on site - I now have 4 different connectors, one of which is supposedly "universal", & guess what - none of them would fit either of the taps at Tackeroo last weekend. And you had to hold the knobs in all the while. :twisted: 

Blow that for a game of soldiers. From now on we fill before we go.


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## RobMD (May 9, 2005)

Given that a vehicle is driven economically (i.e. easy on the accelerator and brakes), if a 'van is driven to the top of a hill it will have stored a quantity of kinetic energy. This will be greater if the 'van is heavier (full tanks).

This is returned when the van travels down the hill, so apart from losses caused by friction, wind resistance, poor driving (unecessary acceleration and braking) etc., the mass of the water has no effect on fuel consumption.
This is also true when travelling along a level road.

A full tank has a lower surface effect than a part filled tank, so will affect stability less. Baffles reduce the effect even more.


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## Boff (May 10, 2005)

Hi!



GeorgeTelford said:


> Thats a little too simplistic, I know there is a vast difference between getting something moving and keeping it moving, but in reality unless you are cruising the flatter sections of Route 66 with no other traffic, then the slow down speed up nature of motoring means we are forever excelerating and descelerating that extra MASS.


No, it is not: The only thing we are looking at her is the _relative increase in fuel consumption_ caused by the _relative mass increase_ from the full water tank.

Kinetic energy (when accelerating) and potential energy (when going uphill) are both proportional to the mass, so an increase of the mass of 3% can *in a worst-case scenario* (steep hills, extremely bad driving habits and air friction neglected) lead to a maximum increase of fuel consumption of also 3%. Provided that conditions are the same except for the water tank, of course.

And as aerodynamic drag makes up for at least 80% of the fuel consumption under normal driving conditions, the maximum increase caused by the above mentioned water tank cannot be more than 3% of 20% so 0.6%. This, as I said, if you are driving "like hell" through mountainous areas.

No matter the economic qualities of the engine etc. as this is all the same independent of the water tank status.



RobMD said:


> Given that a vehicle is driven economically (i.e. easy on the accelerator and brakes), if a 'van is driven to the top of a hill it will have stored a quantity of kinetic energy. This will be greater if the 'van is heavier (full tanks).
> 
> This is returned when the van travels down the hill...


You probably mean _potential energy_ when going uphill.

Unfortunately you are only right if you throw out the gear and let the van roll down the hill without ever using the brakes. I do not really know many hills where you can take that risk. 8O

Nevertheless, just calculate the relative mass increase from the water tank (in my case 150 kg out of 3.5 tons makes 4.3%), multiply it with 0.2 (20%) and you will have the *maximum* relative increase in fuel consumption (0.9% in my case).

Given that my driving style is optimized on fuel economy, I am sure that I can cut that down to half or even lower. Over 500 km, given my average fuel consumption and the Dutch Diesel prices this makes up for about 30 Euro-Cent. A price I am willing to pay for reliable water supply.

Best Regards,
Gerhard


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## Brambles (May 12, 2005)

So, what are the conclusions.
Run on empty water tanks, make sure my gas supplies are low in one bottle and other is empty (even better return empty bottle to Calor and get a voucher to obtain bottle at other end of trip), keep fuel tank on the red topping up at every service station on the way. Oh yes, but food in supermarket near destination and leave the wife at home as that will save weight. Never drive in the dark as that uses more power for the lights, and make sure weather forcast is prevailing winds in the direction I am going.

Whoo Hoo, I am going to save a fortune in running costs. LOL

Seriously though, its all a matter of convenience - full water tanks, gas and fuel. You never know what might happen during the trip to destination so its all a safeguard to protect my comfort an make life simple. I never leave home now without full water tanks if I am staying away the night. It leaves me the flexibility to stop off at a CL or wild camp I wish where water may not be easily obtainable or dark when I arrive. 

You would not dream of only filling your fuel tank half full if going on a long trip so why do the same with the water tanks. Also with less air in water tank with the water sloshing about means less chance of contamination of the water from airborne bacteria.


(Boff - make that 20 cents extra - remember you will need some water anyway - say 1/3 of a tank so you should look at increase in weight of additional water not the whole lot but the we have all overlooked the extra rolling resistance of the tyres due to the extra weight carried - oh dear back to the drawing board. LOL)


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## autostratus (May 9, 2005)

Brambles said:


> .................
> 
> You would not dream of only filling your fuel tank half full if going on a long trip ........................


Diesel fuel stinks!
Despite wearing plastic gloves I always seem to end up with the smell on my hands and it doesn't readily come off. 

For that reason alone I tend to fill up to the maximum and let the tank get down pretty low before re-filling. No argument about weight saving could ever persuade me to do otherwise.


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## RobMD (May 9, 2005)

Ooops boff!!    

I should know better, Kinetic energy is the energy in a body by virtue of it's motion - as you rightly say, the energy in a 'van at the top of a hill is potential energy ( I wasn't recommending freewheeling downhill - although that could be exciting!!). 

The point I was making though, is that a lot of the difference in effort between travelling with an empty tank, as opposed to a full tank is recovered, and the net difference in fuel consumption is very small.

Depending on circumstances, I travel with Full, Part-full or Empty water tanks. Over the past 3 years I have recorded every fill of fuel into a spreadsheet and I haven't noticed any significant difference in consumption due to the state of the tanks.

As a matter of interest, my van is an Autosleepers "Nuevo", with a Peugeot 1.9 Turbo-Diesel (not the later HDi), and my average fuel consumption to date is 26.39 m.p.g. (and I consider myself easy on the accelerator and brakes).


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## spykal (May 9, 2005)

Hi all

Don't forget that a big saving in weight could be made by not laying down any beer, wine or cider supplies or not putting any food in the fridge...all obtainable when "you get there". Now if I could only leave the wife behind too that would be another big saving (in Pounds£££ too)and I could look round the site for a replacement when I arrive .


Mike :lol:


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## DABurleigh (May 9, 2005)

I think I'm like peejay on this. Personally, convenience dominates marginal economic arguments. If I know filling up where I'm going is little more hassle than at home, I'll fill on arrival. Otherwise I'll take anything up to 140 litres with me. And that's a panel van, albeit with 815kgs payload.

I do like my self-contained hot showers; nothing better to give you that warm glow of independence 

I wonder if the must-travel-empty brigade have leftover caravan stability doctrine/ habits.

Dave


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## 89146 (May 15, 2005)

I used to cruise a small yacht singlehanded, often spending prolonged periods (all) at sea, and to an extent the "save weight to save fuel" philosophy applies there to. However, in a boat you cannot always stop where you want, you may not get to where you are planning, so for safety and survival it is essential to keep a minimum stock of food, water and gas on board. Plus spare jumpers! I always had enough to keep me at sea for three days.
I know in a motorhome it is different, there should be plenty of places you can make an unscheduled stop even if it is a service area, but even there have you ever tried to get water? I wanted to fill the dog's bowl once and the only water supply available was hot! If you are making a long trip in difficult conditions, you will need to stop sooner than you think and there may be inadequate facilities, but for safety if not survival carrying a supply of gas and water will ensure reviving drinks in a layby somewhere up the A1 in a snowstorm! Plus diesel - I was always told not to let the tank go below a quarter otherwise the sludge in the tank would start to come through into the fuel system.
Essentially, I bought a motorhome for comfort and convenience, and I enjoy every luxury it offers. I have found myself tiring late at night short of my destination, or realised I would never make the campsite before it shut for the night, and the sheer convenience of stopping in a layby for an hour or more with full facilities "on tap" is unparalleled as a boost to body and soul. So - everything topped right up at the start of the journey. If I wanted to build my character, display economy and be frugal, I would camp in a tent, carry it on my back and cycle to my next destination....THEN weight would be paramount!

Gill


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## RobMD (May 9, 2005)

Cycle to your destination spottydog? - whats wrong with walking!!!

Me - I don't panic about it. 

If I have time and/or it isn't raining hard, I fill up before leaving. If I'm late leaving, or it is too much hassle at the time I leave it until more convenient provided I have enough on board to see me until the next morning (wherever that may be) for drinks, washing etc.


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## 88962 (May 10, 2005)

No-one seems to have said anything about the fact that diesel should be kept full if there is risk of frost. According to those with more kowledge than me this is to help stop it waxing and going thick. So, we always fill up on our return. 

Water carried depends on where we're going and how much time we have.


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## Don_Madge (May 1, 2005)

Dave wrote,

"I think I'm like peejay on this. Personally, convenience dominates marginal economic arguments. If I know filling up where I'm going is little more hassle than at home, I'll fill on arrival. Otherwise I'll take anything up to 140 litres with me. And that's a panel van, albeit with 815kgs payload."

Dave

In the MMM's Buyers guide it shows your Morello as having a pay load of 615 kg. Fresh water tank 72kg. Is this correct?

I'm always very cautious about the manufacturers claimed payload. Our Timberland was 90kg adrift of the manufacturers claim. Still waiting for a explanation 18 months on.

Don


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## spykal (May 9, 2005)

Hi all

Reading various posts it would seem that some manufacturers cheat but the payload calculation should be made with a tank of fuel and water and a cylinder of gas onboard. That way payload means what it says..the amount of extra stuff you can carry.

Mike


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## DABurleigh (May 9, 2005)

Don,

615kg is spec in standard trim. The Maxi option adds 200kg, making 815kg total. This obviously reduces with the weight of other options fitted, and it has not been checked on a weighbridge. 

16 galls fresh water is standard. A 2nd 14 gall tank as option. 30 galls = 136 litres.

Dave


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## Don_Madge (May 1, 2005)

Dave, thanks

All is now clear.

Mike,

The payload area is a minefield and has been for many years. I could tell you of horror stories of first time buyers paying £60,000 for a van to full time knowing nothing about payloads until they visited one of the motorhome forums and then found out they were 450 kgs over weight. I kid you not..

I think you will find at many dealers the sales people are very reluctant to discuss the subject. 

Don


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## 93135 (May 1, 2005)

We always travel with ours full of fresh clean aqua pura.
Whats the point of having an empty tank? you never know when you might want to wild camp.

You should do the maths BEFORE you agree to purchase your motorhome.

ww


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## 89146 (May 15, 2005)

> You should do the maths BEFORE you agree to purchase your motorhome.


Hear hear!

Gill


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## spykal (May 9, 2005)

Did the maths still bought one....maybe an appointment with a psychiatrist is called for.


and re tanks full or empty:

Last summer we spent many great weekends in Wales and each trip we sucessfully managed to sneak a hundred litres of Pure Welsh water back across the border without any problems whatsoever. Not once were we challenged at any border crossing, we do of course take a different route each time we return with a tank full. Next year we are going to try a few trips to Scotland....will whisky damage my tank?

Mike


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## peejay (May 10, 2005)

Whisky on tap. now theres a dream......

Could cause social problems when brushing your teeth though..

pete.


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## hymmi (May 9, 2005)

Just read through some reply's here and picked up something spottydog said about not being able to get a drink of water for her dog because it is all hot.this is not by chance you will never find a cold water tap at the services,it is to stop you having a quick drink from the tap for free,it is typical of the general petty ways in this country.


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## 89146 (May 15, 2005)

The Moto services now have a "dog station" in the main entrance with a bowl of water and some biscuits, free of charge.
With my lot, have to hide the biscuits or they would scoop up the lot, and they usually sniff the water suspiciously and ignore it.
Back to the mineral water (filled from home) bottle in the boot!

Strangely enough they drink the Hymer water which was recently diagnosed as "scummy". Back to the mineral water (filled from home) bottle ............


Gill


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