fuel return line?

I have a 600 gallon tank built into the hull. To my dismay the tank is full of crap that seems to cause a problem when the larger waves agitate the tank. I have two large tank filters that i can alternate to change when underway. the rest of the fuel system is what one would expect on a diesel engine (primary and secondary). This system works but depending on the wave height i might need to change the tank filter every three hours or three trips.

I know a 671 Detroit uses less fuel than it pumps and returns 3/4's of it back to the tank. When it is contaminated once again. I know it is returned hot from the engine and when it goes back into the tank it cools.

I took the return line off the tank and put it on one of the in ports on the secondary filter head. Seems to work fine but some fellow seadogs I trust tell me that may cause problems because of the hot temp of the fuel. The engine may runaway or ????. Some other seadogs tell me it should be alright.

Anyone have a bad experience with what I have done or a positive to add? Is there another way or a different location to put the fuel back in? Is this a going to cause me more problems? The tank is part of the hull and cutting holes to clean the tank out is really not an option due to the boat design.

 

There is another thread giving directions for tank cleanout without removing tank. Empty fuel. Fill with water to drive out flammables. Empty tank again and shop vac crap from low point in tank with a long nozzle. Don't forget step 2 or you may get a nasty surprise.

 

And you HAVE to get the pick-ups into the lowest point of the tank. The last time you want to have a problem is when it is rough.

 

the tank is 21 feet long with a 1 1/2 inch inlet at the rear. Im sure there are several baffles as the fuel does not slosh and come out even in 10' waves.

I could suck out the low part but dont think that would get it all and i am not sure how deep the contaminants are.

I set up a 3/4" pump through the tank filter and went out in 7 to 10' waves one day and cycled the 100 gallons of fuel in the tank for one hour. I still have the same problem. The fuel was shooting out the end of the hose like water out of a garden hose. I was putting the fuel back in through the fill hole at the front of the tank and taking it out the rear of the tank. May have alot of contaminants in the tank.

Any comment on putting the return fuel back in through the secondary filter?

 

IMO, there is no point. You need to get the stuff out of there. There are companies that do this for you...it is expensive. But it is poor design to not have a sump or, at least, a drain, in the absolute lowest part. You will have less HP if your fuel is hot and eventually you'll have to deal with the problem. It is not that difficult to get a pick-up into the low part and you'll suck up junk as you go and catch it with your multi-stage filtration. Hoyt is right about the access holes. It seems a big boat. With big boats come big expenses (or a lot of your own work). Sorry

 

for myself I was thinking of aluminum tanks but still contaminants might get in. When I got my diesel truck its tanks were full of crud and I had to flush them out countless times before I could even think of starting the engine. I guess I'd have to go with Marks suggestion of hiring someone to flush the tanks cause if you dont your never going to completely remedy the problem. That and you might consider replacement tanks if the issue is one of scaling.

my two cents but simply changing the filters every few hours seems like a whopping pain in the ***

cheers and best of luck
B

 

y two cents but simply changing the filters every few hours seems like a whopping pain in the ***

Only if they are not out of the engine space and really EZ to get to.

A good installation its only flipping the valve and changing , with crap fuel drains in a pail , or trough to a tank.

The DD does return most of its fuel filtered ,so there is no gain obstructing the return line , that fuel went thru the primary and secondary filters already


Sounds like you need to "polish" the fuel.

This is a big dedicated pump and set of filters that can run the fuel in a loop , preferably while the conditions are rough to get the most crap.

Usually with enough use the DD will clean the system for you , sounds like a 3rd set of coarse primary filters would be a help.

The traditional set up was the "sock" a large glass jar with a fine cotton filter that would be dumped , at half full.

Your insurance guy may not like that.

The raycor 1000 ganged will do as the filters are cheap by the case.

FF

 

The independent polishing system is the solution. Lots of cruising folk install them because of buying so much fuel in different and unknown places. Racor filter/separators are plentiful on ebay.

 

Filters are expensive. It is way cheaper and better to clean the tank. What is the material of the tank and hull? If there is no inspection plates, cut some and it will give you access to all the tank. With diesel fuel it is fairly safe to clean.

 

ya Im a bit fuzzy on where all this crud is coming from ?

 

http://www.fisheriessupply.com/brand/601796/results.aspx

Is one source for a clean out plate.
There are a number of other aftermarket sources.

"where all this crud is coming from ?"

If the tank is not full the internals can rust

As fuel gets older (very common for cruisers) the fuel clumps together "ashphalting" and wants to return to tar.

The rust is easy to see on the filter ashphalting looks like fine black sand on the filter.

Water in the fuel allows "bugs" to grow at the water fuel interface , there is a lot of fuel (AKA FOOD!) so a real slimey mess is caused.

This looks like Snot on the filter.

No one brand of biocide will kill ALL the different type of growth (regardless of what claims the label has) so splash with your favorite chemicals. We use BioBore for the first shot.

Also some dock supplies are filthy , the reason to use a Baja Filter or a bigger pre filter on the hose , before the tank.

On our 90/90 which is only 33ft an ICW cruise requires multiple fillings of the inshore 24g tank I had the great fortune to find a funnel filter built by Rybovitch -- in Monel!Hate to buy that new today!!!

When filling it does take a bit longer to fill as the diesel goes slowly thru the very fine monel screening.

Even in "good " places , there is frequently some goodies in the bottom of the funnel. Usually if the first gallon or two is OK, the rest will be OK too.

I have at times loaded a single gallon and on inspection decided to fuel elsewhere.

FF

Some comments stolen from another board,,,


FACT: ALL fuel producers admit that diesel fuel is inherently unstable. This instability causes diesel fuels to form sludge and or insoluble organic particulates. Both asphaltene compounds (sludge) and particulates may contribute to build up in injectors and particulates can clog fuel filters plus add to the service issues common to diesel engines.
See: www.chevron.com/prodserv/fuels/bulletin/diesel/L2_2_7_fs.htm

FACT: Diesel fuel contamination problems have two different areas to consider, biology and chemistry. On the biology side is "Fuel Bugs" and on the chemistry side is "Asphaltenes". Thinking you have a biological problem and treating it with a biocide when in fact you have a chemical problem will not solve the problem.

"Asphaltenes" aka diesel sludge is the most common chemical problem and the most misdiagnosed problem in diesel fuel. Asphaltenes are brown and slimy and resemble algae. BUT Asphaltenes are not algae. NO ALGAE GROWS IN DIESEL FUEL. The natural chemical process that goes on in diesel fuel as it ages creates Asphaltenes. The asphaltene molecules will tend to precipitate out of the fuel over time and settle on the bottom of the tank. Once picked up by the fuel pump filters clog and engines stop.

Those that call diesel sludge algae are misinformed and not knowledgeable on the subject and are misdiagnosing the problem.
"Fuel Bugs" aka bacteria and fungus, primarily Cyanobacteria, in diesel fuel are the other problem but less prominent that Asphaltenes. Most diesel users have very little knowledge of this costly problem. There are over 100 types of Fuel Bugs that can live in diesel fuel. Fuel Bugs feed on the oil in the fuel and use the water in the fuel for their oxygen supply. They grow in your fuel at different rates and can easily cost thousands of dollars in damage to each contaminated vehicle.

It is imperative to determine if a fuel problem is biological or chemical based.


FACT: University of Idaho scientists have conducted tests to determine the timeline and percentage of degradation of stored diesel fuel #2. The results of this testing was that the petroleum diesel fuel #2 degraded 26% after 28 days of storage. See: Petroleum and Environmental Engineering Services
Masoud Mehdizadeh, Ph.D. http://www.fueltechinc.com/diesllf.htm

Studies conducted by National Biodiesel Board under accelerated storage conditions also proved that sediments are formed. The formation of these sediments are increased in the presence of water and dissolved oxygen. [See: "Fuel Facts" National Biodiesel Board, Jefferson City, MO; Frankenfeld, J.W. "General Features of Sediment Formation in Model Fuel System," Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 608-614].

Once diesel fuel begins the process of breaking down and sedimentation formation the fuel will create Asphaltene, cluster up, fall out of solution, and settle to the bottom of fuel tanks creating a sludge.

As the fuel further deteriorates, it darkens, produces a foul odor, and often causes diesel engines to smoke. This is a direct result of the early-stage fuel clustering passing through the filtration systems and into the combustion chamber. These clusters cause greater difficulty as they increase in size, failing to burn correctly, thereby exiting the system as unburned fuel in the form of smoke. This problem is exacerbated as the clusters eventually reduce the fuel flow to the point of clogging the filters. Filtration does not solve the core issue.
Contact us to assist you with your fuel

FF

 

The fuel tank is part of the hull. The hull is fiberglass. I not positive but most likely the tank and its sides are fiberglass over wood. Due to the boat design its not possible to cut holes for access into each baffled area.

I believe the contaminate(s) were algae. Where I went wrong was to put a biocide in the fuel. Pretreatment, the contaminants were large clumps easily filtered. Once I put the treatment in the tank the clumps broke up into a fine black particulate which plugs the filters even faster.

I know I will have to clean the tanks and that is in the works. I really was wanting to know about the fuel return line.

I will check on the filters suggested. I have been looking for some kind of filter to pull out the particulate and drain it off. Research on the web I found about the particulate in question states it is 30 microns in size.

 

If you added any methylene to the fuel, the fiberglass may be breaking down. There are other solvents that may cause that too.

 

Algae needs light to grow...so, you will agree, it is NOT algae. Bite the bullet - install ports (no matter how much you don't want to. Fiberglass tanks are the best and it will be worth your while to do them right with ports for cleaning. What makes you think there is pluywood? you need to find out if it has fuel in it, if it is there.
If not wanting to make them right, get rid of them and build other tanks but just don't leave a bunch of scuzzy fuel down there.

 

Algae grows in tanks without light. Biocide can kill it, but it will not clean the fuel.