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Old 09-16-2019, 02:07 PM   #1
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Always fill up the gas tank or ??

In order to watch my MPG on the class A RV we bought in March of this year I tend to always fill up when it half a tank or so. The 80 gallons of gas weighs about 504 pounds so for our short 2 to 3 day weekends at a state park 60 miles from home it seems I'm wasting some MPG carrying all that fuel.

Do most experienced RV'ers run with partial fillups? And then to see overall MPG fill up every so often.

There's no water hookup at this state park that we frequent so normally it's a full tank of water but this past weekend we've only used 1/2 which seems typical for a 2 night stay. I dumped the other 1/2 when we left and think I'll try filling up there instead of at home.

Thanks... Ron (2019 HR Vacationer 35P)

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Old 09-16-2019, 02:26 PM   #2
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I understand your reasoning for wanting to reduce weight in order to eek out a little better fuel economy. The problem is water, not in your fresh water tank but forming in your fuel tank. When you park any vehicle with less than full fuel tank, it has the potential to condensate the moisture in the air in the tank.

Ethanol gas loves moisture which is bad for your fuel lines, injectors and engine. Diesel fuel also loves moisture where it can grow algae to plug up fuel filters and injectors. Your best defense is to keep the fuel tank full while in storage. Much cheaper to keep the tank full than pay to have a fuel tank dropped and cleaned.

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Old 09-16-2019, 02:31 PM   #3
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If you have a tank that is 1/2 full and it's a metal tank it will form condensation on the upper side of the tank, then you will have water in the fuel.

I have a steel tank and never let it set without getting it filled.
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Old 09-16-2019, 03:22 PM   #4
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Always full. Any incremental increase in MPG is incidental to having a healthy
fuel tank for me.
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Old 09-16-2019, 03:38 PM   #5
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You will never keep a full take if you a using it. I could see a problem in the winter time with a half a tank sitting for extended periods of time. What about all the millions of cars that are driven much by the little old ladies that just go to church a back. I drive mine till it needs fuel then fill up and never had water in separating bowl.
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Old 09-16-2019, 04:02 PM   #6
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My rig weighs over 28,000 pounds loaded. 500/28,000 = less than 0.018. We're talking about less than 1.8% of my total weight. I could not possibly care less, or better stated, I have a lot more important things to care about. I'd rather have the fuel for my genset than the immeasurable and unimaginable extra mpg.
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Old 09-16-2019, 04:11 PM   #7
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You may find that your MH rides better with full fuel and full water, and has no real affect on MPG. Plus as others have said, better to have full fuel while in storage.
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Old 09-16-2019, 04:25 PM   #8
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My MH always goes back to storage with a full tank. We live in earthquake country and now the electric utility company is talking of multi day outages when the fire danger is high. That means gas pumps won't work.

We have already used the MH generator to run our home refrigerator and our freezer when the power was out for 3 days. It only makes sense to me to be fully prepared for any emergency.
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Old 09-16-2019, 04:37 PM   #9
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I am also a keep it full person. Better to have the fuel when you need it and to run the generator.
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Old 09-16-2019, 05:01 PM   #10
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I commend you for wanting to be practical and asking the question about filling your tank.

Other answers are correct - better full than empty and you won't save much money by lightening your load.

I guess the answer is that you should always fill before going home and "storing" for a few weeks before the next trip. Other than that using up 1/2 a tank to get to a campsite and then staying a weekend will not be a big problem for you. - But, if you're staying for a month - you should try and "park" with it full.
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Old 09-16-2019, 05:53 PM   #11
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You wont notice a bit of difference in MPG, and I dont always top off when coming home, after a long trip it's the last thing on my mind and I have not had any problems with water in my fuel. I will fill it up for winter storage and by the time spring gets here I have burned just over 1/4 tank running gen. A few times and coach at high idle amazing how much it uses not going anywhere lol
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Old 09-16-2019, 05:56 PM   #12
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I agree with both answers. I had 3/4 tank last week and took a 125 mile trip to and from from a campground. I now have a 1/2 tank. I always use Biobor jf in my tank at every fill, so I don't worry about nasties in the diesel, I have a water separator in the line - haven't seen any water and the engine runs good. My fill up is usually a 1/2 tank so when I leave home again it is fill-up time (75gals) with more Biobor Jf.
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Old 09-16-2019, 06:39 PM   #13
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I top off the tank right before the border crossing into California then put in only as much as I absolutely need to get me back out of California.

Otherwise I fill the tank completely every time I fuel up.

When the coach goes into storage I like to run it fairly low. This way I don't need as much fuel stabilizer for the fuel in the tank and the fuel in the generator carburetor.

Been doing it this way for 15 years without ever having a problem with water in the fuel.
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Old 09-16-2019, 06:39 PM   #14
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I wonder why it matters what mpg you get, I never check, I don't care, I didn't buy anything to save gas, if I wanted to save gas I would stay home.

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