I know water in the diesel tank is part of having a diesel engine on a boat. 100% humidty is part of life in Louisiana. It is my understanding that the tank heats up in the day driving out air. Then at night when the tank cools off and moist night air is sucked into the tank. Then the moisture condenses on the tank walls and drops to the bottom of the tank. This weekend I pumped out at least a half gallon of water out of my tank. I was wondering if putting a valve in the diesel tank vent line next to the transom would cause any problems I am not thinking of. I know opening the valve will be one more thing to do before going out. I have a new fill cap on my diesel port. I know it is not leaking. Thanks for your input. Tom Wingo
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Vent Valve
Tom The cool moist air doesn't get in through the vent line and so won't be solved by a valve. The "daytime" air is still in the tank, isn't it? It cleverly snuck in while the valve was open. So, you close the valve on the vent line before you leave the boat. But air is already inside. When it cools off outside at night, the whole boat, including the tank, the fuel and the air in the tank, will also cool off. The moisture is already in the daytime air. So, what's the valve doing? Nothing. Save on the valve. Buy some water zorb liquid and put it in your tank with the anit-algae stuff and keep draining your fuel filer/water separator regularly to avoid water getting in the injectors. And, of course, keep your tank reasonably full to reduce the amount of empty space in the tank. Stu
Tom The cool moist air doesn't get in through the vent line and so won't be solved by a valve. The "daytime" air is still in the tank, isn't it? It cleverly snuck in while the valve was open. So, you close the valve on the vent line before you leave the boat. But air is already inside. When it cools off outside at night, the whole boat, including the tank, the fuel and the air in the tank, will also cool off. The moisture is already in the daytime air. So, what's the valve doing? Nothing. Save on the valve. Buy some water zorb liquid and put it in your tank with the anit-algae stuff and keep draining your fuel filer/water separator regularly to avoid water getting in the injectors. And, of course, keep your tank reasonably full to reduce the amount of empty space in the tank. Stu
Stu is right
You're getting normal air and condensation in the tank. The easiest thing to do is get some treatments and keep your tank as full as is reasonably possible.
You're getting normal air and condensation in the tank. The easiest thing to do is get some treatments and keep your tank as full as is reasonably possible.
Fuel Cap
I know you said the fuel cap was replaced, it could have been as simple as a bad "O" ring on the fuel cap. These split after a few years and rai & deck wash water gets into the fuel past the bad "O" ring. If in the future if you find a bad "O" ring take the one off the potty tank pump out cap--more water in that tank wount make a lot of difference, then get some new "O" rings. I found some Toyota O rings fix well and are available at any auto parts store. Dave
I know you said the fuel cap was replaced, it could have been as simple as a bad "O" ring on the fuel cap. These split after a few years and rai & deck wash water gets into the fuel past the bad "O" ring. If in the future if you find a bad "O" ring take the one off the potty tank pump out cap--more water in that tank wount make a lot of difference, then get some new "O" rings. I found some Toyota O rings fix well and are available at any auto parts store. Dave
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