# Keep Boat's Fuel Tank Full Or Not ?



## Capt Rick (Jan 6, 2008)

I have always kept my boat's fuel tank full in the past to prevent condensation/water build up.
I have heard recently that you shouldn't do that now because of the ethanol in gas, and should only put in the amount of fuel you are going to use for the day's trip. 
Are there any mechanics out there who can advise on this ?
Thanks in advance for your reply,
Capt Rick


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## sealark (Sep 27, 2007)

Capt Rick I am no mechanic but I have always done what you do and will continue to keep my tank topped off immediately after every trip. I have never had before or after ethanol had a problem with water. My theory is ethanol cant MAKE water. And a full tank wont condensate like a partially full tank. I do use my boat year round and I have three filters on the rig that I have never had water in any of the filters. I have a sediment filter, a cartridge filter and the engine filter on my 150 E-tec. Hope this answers your question. If you kept you tank full in the past, Have you ever had a water problem? If not then there is your answer.


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## Firefishvideo (Jul 1, 2010)

http://www.fuel-testers.com/marine_boat_ethanol_problems.html
Here is a link to info on ethanol fuel/problems.
The main problem with ethanol is that the alcohol in the mix "sucks" the moisture right out of the air and into your tank.
Cars have a closed fuel system which keeps the moisture out, but boats have an open vent, which lets it exchange air, and moisture.
...So what ever you can do to minimize this will help. I can definately see the full tank not sweating on the inside, but also, if it is full to the brim, It might not have a large surface area of fuel to react with the air.
Them best thing to do is use it regularly, to take me diving!:whistling:


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## sealark (Sep 27, 2007)

I have an open vent but it's connected to about 5 foot of hose between the vent and tank. I don't know but I'll keep my tank full and keep using the thing regularly. And of course keep my fingers crossed...:yes::yes::yes:


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## 20simmons sea skiff (Aug 20, 2010)

use marine stabile also, good stuff, or equal,


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## courantpublisher (Jan 13, 2009)

*2nd on Stabil*

I 2nd the Marine Stabil. Make sure it is the marine variety for better results and try to run your motor(s) regularly, even if it is just on the muffs.


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## woody (Oct 17, 2007)

A fuel/water separator from Racor will end your troubles. Just make sure it has a clear lexan/plastic lower unit so you can see & drain the accumulated water.........


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