Fuel Tank Issues

[JLR]

One of my four fuel tanks has salt water in it. That tank was used exclusively by my starboard engine. The fuel side of the tandem boost/fuel cooler was pressure tested and is fine. I am now having the salt side of the cooler tested. These are on a 1292 DDEC. Aside from an actual leak in the tank itself, which seems unlikely, how would salt water get into a fuel tank if the fuel side of the cooler tests fine? No rough water to permit entry through the vent and the amount of salt water is something to be concerned about. Also, this happened when the tank was almost full. The same fuel source and hose was used to fill my other three tanks and the fuel polisher tested those tanks and they are fine. Kind of stumped on this one and I guess, hoping the salt side of the cooler has a leak.

 

[Avenger]

Faulty deck fills or a vent problem.

 

[kelpy]

Is your fuel cooler in line with the raw water supply from one of the water pumps to the heat exchanger? What is a "tandem boost/fuel cooler" on a 92 series engine?

 

[Boatsb]

How do you know its salt water?

Could there be a leak on the tank top allowing water in somewhere?

Did you double check the fill cap o rings?

 

[JLR]

Fill cap and o rings have been checked. Salt water confirmed by fuel polisher with some sort of test and by taste. Any other possibilities?

 

[oldawg]

If detected by polishing, how do you have any idea when it got in there? May have been there for years.

 

[rustybucket]

I'd vote for fill cap or vent. You said you tested the fill cap, did you test/check the vent and line?

 

[Play'N Hooky Too]

Leaky fuel fill cap and repeated use of raw-water washdown could be the culprit.

Your polisher is awful brave to be "tasting" water from the bottom of a fuel tank....

 

[Canuck Dennis]

Depending exactly where the vent is , if you fuelled up in fresh water adding lots of weight and the vent managed to suck in some salt water when you relocated, could be a possibility.

 

[JLR]

My prior reply got lost. It's not the vent or the O rings. The vents are way high and the o rings were checked. There is no salt water washdown so that is out. It might have been there for awhile but I doubt it. Having owned the boat for the past five years, I suspect I would have known. I need to find the source to avoid pumping salt water through my injectors. It had already gotten into the racor. I pumped out ten gallons of salt water from this 550 gallon tank. That is not good. I wish I knew how salt water could get into the fuel if the fuel side of the cooler tested tight. I really hate to ask but is there any chance the tank itself could have a leak to permit salt water to enter from the bottom? Doubt it by better to ask than not.

 

[SeaEric]

AFAIK the tank bottom is independent of the bottom of the boat. Now, if you were riding on an aluminum Burger - the answer would be different!

 

[johnjen50]

If u had a leak in the bottom sections of the tank the diesel would flow out before water would flow in. What about the top of the tank? Is there any possibility bilge water could be draining into your tank from top sides of that?

 

[johnjen50]

Or the more I think about it perhaps pressure could force water in, but only if it were on the bottom and part of the hull. As Eric said if it is not, then I think it’s a stretch to say it’s working in from the bottom up.

 

[JLR]

Ruling out from the bottom up is very reassuring. Darndest thing. I will not know about the salt side of the cooler until it is pulled and tested next week. If that is not it, I am stumped. And if it is it, I still do not understand the physics of how it got into the tank.

 

[Avenger]

If the one cooler doesn't turn up bad you may want to check the other one. My boat had a plumbing mix-up in the fuel lines and we were not operating from the tanks we thought we were.

 

[kelpy]

Did you rag on the sailboater down the way about hanging his laundry out to dry on the lifelines and he retaliated by pouring a couple buckets of seawater into the dockside tank fills?


In getting back to your problem, a 92 series engine usually has the fuel cooler on the left (or right) side of the engine in line with the seawater supply pipe from the pump to the heat exchanger inlet. Again I need to ask, to satisfy my own curiosity, what is this "combination boost and fuel cooler" that you speak of.

 

[SeaEric]

Ruling out from the bottom up is very reassuring. Darndest thing. I will not know about the salt side of the cooler until it is pulled and tested next week. If that is not it, I am stumped. And if it is it, I still do not understand the physics of how it got into the tank.

Fuel return lines?

 

[JLR]

Did you rag on the sailboater down the way about hanging his laundry out to dry on the lifelines and he retaliated by pouring a couple buckets of seawater into the dockside tank fills?


In getting back to your problem, a 92 series engine usually has the fuel cooler on the left (or right) side of the engine in line with the seawater supply pipe from the pump to the heat exchanger inlet. Again I need to ask, to satisfy my own curiosity, what is this "combination boost and fuel cooler" that you speak of.

I am not certain but am told it is both a boost cooler and a fuel cooler.

 

[dsharp]

Is the cooler mounted before or after the fuel p?

 

[kelpy]

I would be interested to see a pic of this "cooler". The fuel cooler should be mounted before anything other than the raw water pump. The return fuel line goes to it, from there to the DDEC computer coolers and back to the tank.

Your 12-92s has the aftercoolers under the blowers so ther aren't any external boost coolers like a 71 series engine has. Do your engines have the factory heat exchangers or the big Sen-Dur cylindrical heat exchangers mounted remotely along side the block?