Topping Off Fuel Tank?

[gelsw]

With a 90 gallon tank I am thinking keeping it only about half full while driving just to keep from hauling all that extra weight around. With diesel weighing about 7.5 pounds per gallon that is an easy weigh to drop 300 + pounds. Still would have about a 300 to 400 mile range between refueling. 

The other school of thought I am aware of is keeping the tank topped off to avoid condensation in the tank.

Suggestions anyone?

Gary

[hermanmullins]

Gary,

Partly yes and partly no. When on the road we always leave any over night stop with empty holding tanks and 1/2 full of water. Any time I stop for fuel I will fill up completely. I don't like to stop so often, wait in line for the next pump and have to do it all over again so soon. I average in the 7.9 to 8.0 GPM with a full tank (130 gallons) or with a 1/4 full tank, about 30 gallons.

When we travel with friends we will always top off when the one with the smallest tank needs to fill up. Doing this means that we wont have to stop later to fill our tank and they are still half full. (just being a good friend)

I also stop and top off my tank when we are about 30 miles from home so the tank will be full when it goes into the garage.

Herman

[kaypsmith]

I don't know which to reply to! Well here goes my assessment, I have a 150+ tank, when arriving home, I go to the nearest fuel stop, 4 miles from the residence, I do top off the tank. So it sits at this location, sometimes two weeks, sometimes three months, depending on the time of the year. When I get ready to leave home, the coach is always ready to go. This keeps down worry about condensation in the tank, and I do add algaecide just before the winter months, which is when it does sit for the longest period of time. The coach is capable of carrying the weight, and it does get lighter as you drive.

[BAMABOB]

I would add that it also depends on where you live. We are in the deep south so we keep the tank (150 gal) topped off and use Sta-Bil fuel stabilizer (All the time actually )

[wolfe10]

It is very important when you store you coach to have a full tank to minimize condensation.

Reasons to "live off the top half of your fuel tank":

Most DP fuel tanks are well forward, where they help with weight distribution-- always an issue on a DP with so much weight in back. With most gray and black tanks in back, they detract from better weight distribution.

Modern diesel engine are "high bypass".  For every gallon of fuel that goes to the engine, you only burn an ounce or two. The remainder is used to lube and cool injector and engine parts and returns to the fuel tank. Cool fuel is better. Next time you drive on the lower half of the tank on a hot day, reach under and touch the fuel tank-- it WILL be hot.

Weight is an important factor on fuel consumption on grades-- not so on flat ground where aerodynamic drag is by far the largest factor.

Let's see the percent increase in weight by carrying 300 pounds more on a 30,000 pound coach: ya, 1%.  Not significant.

 

 

[wildebill308]

7 hours ago, ShortBus said:

With a 90 gallon tank I am thinking keeping it only about half full while driving just to keep from hauling all that extra weight around. With diesel weighing about 7.5 pounds per gallon that is an easy weigh to drop 300 + pounds. Still would have about a 300 to 400 mile range between refueling. 

The other school of thought I am aware of is keeping the tank topped off to avoid condensation in the tank.

Suggestions anyone?

Gary

Gary, always work off the top 1/2 of the tank. I start looking ahead for a good fuel stop at 1/2 that way if the first couple of places are going to be hard to get in or out of I can keep going. I will bet you can't tell the difference in milage. I travel on the top of the fuel tank and with 1/2 water and empty holding tanks.

One other reason to use the top of the tank is your generator will shut down when you get below 1/4 tank.

Bill 

[BAMABOB]

5 hours ago, WILDEBILL308 said:

Gary, always work off the top 1/2 of the tank. I start looking ahead for a good fuel stop at 1/2 that way if the first couple of places are going to be hard to get in or out of I can keep going. I will bet you can't tell the difference in milage. I travel on the top of the fuel tank and with 1/2 water and empty holding tanks.

One other reason to use the top of the tank is your generator will shut down when you get below 1/4 tank.

Bill 

Yepper! Our Mantra is 1/2 a tank = Empty

 

Also, what wolfe said: in the grand scheme of things, 75 GAL of diesel weighs just over 550 Lbs which in not much in a 44K GWVR Coach

[campcop]

I like to live dangerously, I fill up between 1/4 and 1/2

[obedb]

When you run anything diesel powered out of fuel, you will know what not to do in the future?.

[CarlAda]

3 hours ago, ObedB said:

When you run anything diesel powered out of fuel, you will know what not to do in the future?.

got that right!

[kaypsmith]

That is a definite NO!NO!. I limit to 450 miles, have no fuel gauge. Usually takes 60 to 75 gallons to refill, depending on driving conditions.

[wildebill308]

I would bet a 6 pack that if you ran 10 tanks both ways you wouldn't be able to see a difference that you could point to and say it was the weight. There are so many other things that affect mileage. Here is something you might like to read. Not all applies to driving a motorhome but it is informative.

https://cumminsengines.com/brochure-download.aspx?brochureid=104

Bill

 

 

[jleamont]

20 hours ago, WILDEBILL308 said:

Gary, always work off the top 1/2 of the tank. I start looking ahead for a good fuel stop at 1/2 that way if the first couple of places are going to be hard to get in or out of I can keep going. I will bet you can't tell the difference in milage. I travel on the top of the fuel tank and with 1/2 water and empty holding tanks.

One other reason to use the top of the tank is your generator will shut down when you get below 1/4 tank.

Bill 

This is exactly how I run ours! At a 1/2 I ask the DW to look ahead for the best bargain on fuel with gas buddy app. She tells me what is ahead and I make the decision where to stop.

I also try to keep it full for the reason Brett mentioned, the fuel tank gets hot with returned fuel from the engine which will create more condensation in the tank and also for weight distribution. I have a 14,600lb steer axle, my fuel tank runs parallel to it (just behind the axle, genset hangs out in front of it) my holding tanks are just in front of the drive axle, due to the high capacity of the steer axle I try to keep weight up there for handling. I also do not like to run below 1/2 since our last coach, you had to be careful, if you went below 1/2 your distance was not good, and you had a great chance at running out of fuel, especially when you could watch the gauge drop if you sunk your foot into it.

[CarlAda]

Enjoying reading this thread.  I typically top off around the 1/2 full mark, and certainly never let it get below 1/4.

[OkieDave]

The only time that you have too much fuel is when you are on fire.

[casuall454]

I would be more concerned with "fluid surge" and condensation.

As the fuel tank isn't baffled the tank 1/2 filled will allow for fluid surge during heavy braking and turning. This could become a factor during rain or roads that are poorly maintained.

Secondary concern is 1/2 filled tank allows for condensation to accumulate inside the tank.

Safe travels.

[wildebill308]

11 hours ago, Casuall454 said:

I would be more concerned with "fluid surge" and condensation.

As the fuel tank isn't baffled the tank 1/2 filled will allow for fluid surge during heavy braking and turning. This could become a factor during rain or roads that are poorly maintained.

Secondary concern is 1/2 filled tank allows for condensation to accumulate inside the tank.

Safe travels.

I think the "fluid surge" problem would be minimal. How much is a few hundred pounds sloshing around going to effect a  30,000+ coach. Kind of like leaning into the turn. The main problem is as Brett mentioned the fuel is used to keep components cool less fuel less heat sink. The other thing is not getting into a bind for fuel. Back in the day (as they say) I was driving a class C Ford chassis when one of the fuel pumps decided to quit.  We were on a trip so I decided to wait till we got home to fix it. That left me with a total usable fuel capacity of about 18 gal. That gave me a range of about 175 miles. On one leg out in west Texas I was getting below 1/8 tank. pulled in and found out the pumps were down. I asked where the next gas was and was able to get there with the low fuel light on and some sweat on the brow. I don't run on the bottom half of the tank thank you.

Bill

[gelsw]

Wow!! this the most informative thread yet.

I knew nothing about the fuel being also used for cooling the engine. While it was obvious to me about keeping a full tank when in storage I was thinking of the traveling we do in the west with the mountains and all, but you have me convinced, work off the top half or even third of the tank. We need to stretch frequently, i.e. we know every rest area on 10, 40, 70 and 80 between Ohio and California. Reminds me of my boating rule of thumb, 1/3 out, 1/3 back and 1/3 in reserve, which I have had to dip into more than once.

Thanks everyone, I am amazed at the wealth of knowledge here!!

Gary

[tbutler]

I manage our fuel level based on fuel prices.  With an 127 gallon tank, at 8 miles per gallon I have a range of over 1000 miles.  Now I know you can't use every drop of that fuel but I'll decide when to fuel based on prices, where we are and where we are going.  Traveling 800 miles you will pass a wide variety of fuel stops.  We frequently run from St. Louis to Sacramento, grandchildren in both places!  As we go west, fuel prices climb pretty consistently so I'll fuel in Cheyenne where the prices are usually lower than in Nebraska or Utah.  Then at Evanston or Green River, WY I'll stop and top off the tank before heading into Utah unless the Salt Lake City area has lower prices.  Crossing Nevada I'll look for the area with the lowest price and fuel there and then make one last stop in the Reno area to top off the tank.  If I can get into and out of California without purchasing fuel I've managed my fuel well.  I use the Flying J web site to get a general idea of fuel prices across my route of travel.  I use Gas Buddy to find the lowest price station in the area that will accommodate a large vehicle and if convenient will use that station.  You can't drive many miles out of your way with a coach to save a few cents on fuel but if you can take advantage of the price differences on your way, you can keep the cost to the minimum.  On trips in the opposite direction, my usual practice is to run the tank down to the lowest price area we can reach.  Lately many of my earlier practices have been modified as fuel prices have become a lot less predictable than they used to be.  Missouri used to be the lowest price fuel on our route and one of the lowest in the US but not so much lately.  Occasionally fuel in Colorado is below the price in Cheyenne.  One never wants to go into Canada with an empty tank and you never leave Canada with a full tank!  It's just one of the things I watch to try to make our travel budget stretch as far as it can.

As to the cooling of the engine, that is a minor benefit (or just a side effect) of circulating the fuel through the engine.  The fuel tank makes a lousy heat sink.  The tank warms up but doesn't radiate heat worth a darn.  If it was really carrying a lot of heat from the engine to the fuel tank, it would be boiling like the engine coolant would if it weren't pressurized and constantly circulating through the radiator.  I've never seen the engine temperature change because the fuel tank is low on fuel.  Engine temperature is managed by the coolant system.

We run with a quarter tank (32 gallons for us) as the lower limit in hot weather so we have the house air available for cooling while traveling.  In cold weather we'll stretch that a bit but at 20 gallons I figure the sloshing of fuel could result in air being drawn into the fuel intake at some point so I never let it get that low.  We have a fuel monitoring system on board, the Aladdin system indication of fuel level is within a gallon of the fuel I add when filling the tank most of the time.  When the dash fuel gauge indicates a half tank, we are really at a quarter so I never trust it.  If we are running the generator on a trip, during the day or overnights, the Aladdin system doesn't account for that so I have to factor that in to be as accurate as possible with the fuel level.  I figure 1/2 gallon an hour which includes a fudge factor to make sure I'm not underestimating fuel usage.

One other factor to consider.  Starting out in the spring with a full tank of six month old fuel in the tank, running the tank to a quarter tank then filling it puts a majority of fresh fuel in your tank right away.  If you do that again, the amount of old fuel goes from 1/4 to 1/16 and very quickly becomes a minor amount of the fuel you are burning.  If you fill at 1/2 tank each time it goes 1/2, 1/4, 1/8, 1/16.  You see where I'm going.  I want to use as much of the winter fuel as I can when I start my summer travels so I consider using as much as possible from the tank as a way of flushing out the stale fuel as quickly as possible.  The fall/winter mix and the fuel stabilizer are out of the tank well before I hit really hot weather.

[wolfe10]

Tom,

I do exactly as you do, use http://then.gasbuddy.com/

I enter a city on my route that I will reach with 3/4 tank of fuel (the shortest distance I am willing to make a stop for).

Then click on "MAP".

Reset it to diesel (or whatever fuel you use-- default is regular unleaded).

Scroll along our route for the day/next couple of days.  Can scroll a couple of hundred miles in 2-3 minutes.

Click on a station what shows a good price.

IMPORTANT: Copy and paste the address of that potential station into Google Maps.

Use both "earth view" and "street view" to verify that the station is "RV friendly.  And often, the street view will even be detailed enough to allow you to locate the diesel pumps (either additional hose and nozzle or diesel powered vehicle in photo).

In the days of $.03-.05 per gallon difference, it was not worth the effort.  But, today you can save $.25-.30 per gallon.  Well worth the effort.

[jleamont]

On May 6, 2016 at 4:17 PM, OkieDave said:

The only time that you have too much fuel is when you are on fire.

This is where a "like button" would come handy .

shorbus, you will find a lot of good information on here from mostly friendly people. 

[wildebill308]

59 minutes ago, jleamont said:

This is where a "like button" would come handy .

shorbus, you will find a lot of good information on here from mostly friendly people. 

We had a like button but they didn't give any guidance on what it was and how it was supposed to function before it was taken away again. There were several features like that, no one explained the changes and the when someone asked about it they were taken down.

Bill

[obedb]

I have seen saddle tanks on 18 wheelers in the winter throwing almost a fog out when you remove the fuel caps for refueling. The tanks  actually felt warm when you put your hand on the tank below the fuel level.  The 3406 E Cat model was the most noticeable, but then motorhomes don't have saddle tanks?. Must be my old brain mystifying things. I had twin 150's.  The injectors were cooled by the circulating fuel or so I was told. Maybe it was just a CAT thing?.

[obedb]

Bill/ whaddyou me a mostly friendly??  RodgerS hasn't been around for awhile?.