37c fuel tank cleaning

[Cocoa Beach Sailor]

First picture is looking through the hole that the fuel gauge sits in on the fuel tank, down at the fuel intake pipe. Second picture with the red arrow shows the end of the pipe where fuel is sucked up and delivered to the engine. Obviously there is way too much gunk in that fuel tank. You can see from the filters how nasty it was. I used a little electric pump to empty the fuel tank out into 6 gallon Jerry cans. It is a 38 gallon fuel tank according to the tank tag. I'm going to use one of my outboard motor fuel tanks and fill it full of diesel and use that to run the motor with until the main tank is cleaned.
Cleaning the tank will be accomplished by putting about 10 gallons of gasoline in it and hooking up an electric fuel pump that will draw fuel out of the tank, through a filter, through the pump and then back into the tank via the fuel return fitting. The pump will cycle continuously and I will check the filter often as I'm sure that I will need seven or eight of those clear filters that are 20 micron. Once I get out sailing in open ocean, the 10 gallons of gasoline in a 38 gallon tank will slosh around real good and the solvent action of the gasoline will dissolve all of the gunk and I figure by the time I get to Brevard I will have dissolved everything that needs dissolving and then I will pump the gasoline off through a smaller filter, 10 microns as opposed to 20 microns, and I will put it in my car's gas tank. The car has a single throttle body injector so the orifice isn't so picky. but a 10 micron filter should have the fuel clean enough to use regardless.
I could have built my dream catamaran with all this money and effort!( been working on the boat full time for 4 months) But having a fuel issue and having to change a fuel filter, and it's always at a very inopportune time, middle of the night big waves nearing a lea shore, is no fun. If I ever get the thing in the water before I croak, it will be reliable! Me on the other hand, I'll never be reliable.

 

[RitSim]

On my previous Catalina 30, I opened the fuel gauge hole and saw gunk. I thought it would be nearly impossible to clean the tank thru the gage hole. I used a 3" hole saw to cut an access hole. My tank internals were all covered with a dark film but little of it was loose. Purged the tank and hung a low voltage light thru the gage hole. Used a solvent to clean the tank insides completely. Cut a piece of 3/16 aluminum into a 4.25" circle. Carefully marked 24 holes and drilled with the tap drill for #10 screw. Marked the lid location on the tank and used the drilled cover as a template. Checked the tank interior for chips. Then tapped #10 machine screw threads into the tank. Drilled the cover plate holes to clearance holes for #10. Cut a rubber/cork gasket (diesel tolerant) and installed the cover. worked for years with no cover leaks.

 

[Cocoa Beach Sailor]

Quite some time ago I was in a Endeavor 32 and an attendant put gasoline in the diesel tank. I pumped off all of the gasoline and then filled it up with diesel. The gasoline that was in there had loosened a ton of crud and I went through three sets of filters within several hours back out Oceanside of the keys. The solvency of gasoline is very strong. I feel confident that letting 10 gallons of gasoline slush about in a 38 gallon tank for several days while sailing offshore On My Way South will clean the tank entirely and I won't have to mess about with cutting holes or tapping.

On my previous Catalina 30, I opened the fuel gauge hole and saw gunk. I thought it would be nearly impossible to clean the tank thru the gage hole. I used a 3" hole saw to cut an access hole. My tank internals were all covered with a dark film but little of it was loose. Purged the tank and hung a low voltage light thru the gage hole. Used a solvent to clean the tank insides completely. Cut a piece of 3/16 aluminum into a 4.25" circle. Carefully marked 24 holes and drilled with the tap drill for #10 screw. Marked the lid location on the tank and used the drilled cover as a template. Checked the tank interior for chips. Then tapped #10 machine screw threads into the tank. Drilled the cover plate holes to clearance holes for #10. Cut a rubber/cork gasket (diesel tolerant) and installed the cover. worked for years with no cover leaks.

 

[shemandr]

There are services that will come to your boat and polish your fuel, and/or clean your tank. No fuss. no muss. Just write the check and get on with your life.

 

[Jim Legere]

Cleaning the tank will be accomplished by putting about 10 gallons of gasoline in it and hooking up an electric fuel pump that will draw fuel out of the tank, through a filter, through the pump and then back into the tank via the fuel return fitting. The pump will cycle continuously and I will check the filter often as I'm sure that I will need seven or eight of those clear filters that are 20 micron. Once I get out sailing in open ocean, the 10 gallons of gasoline in a 38 gallon tank will slosh around real good and the solvent action of the gasoline will dissolve all of the gunk and I figure by the time I get to Brevard I will have dissolved everything that needs dissolving and then I will pump the gasoline off through a smaller filter, 10 microns as opposed to 20 microns, and I will put it in my car's gas tank. The car has a single throttle body injector so the orifice isn't so picky. but a 10 micron filter should have the fuel clean enough to use regardless.

Well, let us know how it works out for you. Messing around with gasoline in diesel system would not be my preference. Remember: gasoline is highly flammable; diesel is not. At least ensure your electric pump is ignition protected and all hoses are rated for gasoline. I would prefer kerosene as a 'solvent' but installing a proper cleanout hatch near the tank gauge hole (as I did on my H37C) is the proper way to clean out the sludge in the tank. YMMV.

 

[Cocoa Beach Sailor]

This boat is bleeding me in both time and money and I have to draw the lines somewhere and putting an access to clean the tank out properly just as too much hassle. I used to drag race cars and I have all the gasoline rated fuel line pumps Etc ignition protected. If I used anything other than gasoline then I would have the problem of disposal which I do not have with the gasoline. However, I already found one Pitfall and avoided it. When these tanks were built the cork on the fuel gauge was covered with shellac which is resistance to gasoline, up until they started putting ethanol and gasoline. So I will put ethanol-free gasoline in the tank and according to both Marine people and people who restore old old cars, coding the cork with super glue is a good idea which I already did. I'm still about a week and a half out from splashing the boat. I'll update later. I'm thinking gasoline because I accidentally had gasoline put in my diesel tank on a different boat and we immediately pumped all of it off that we could get but just it being there for a couple hours released all kinds of gunk in the tank and I went through three sets of filters within just a couple hours time once I got back out Oceanside to the keys.

Well, let us know how it works out for you. Messing around with gasoline in diesel system would not be my preference. Remember: gasoline is highly flammable; diesel is not. At least ensure your electric pump is ignition protected and all hoses are rated for gasoline. I would prefer kerosene as a 'solvent' but installing a proper cleanout hatch near the tank gauge hole (as I did on my H37C) is the proper way to clean out the sludge in the tank. YMMV.

 

[colemj]

There are a few issues with your plan. First, to run off an outboard tank, you will need to provide for the diesel return. You can't just have the engine intake to the tank. Second, those little in-line filters you are using are completely inadequate. You will need a real filter, and the larger the better. Lastly, as @Jim Legere mentioned, you really need to make sure any pumps you use with gasoline are rated for that.

A polishing service like @shemandr suggests will use pressurized fuel to blast inside the tank. Depending on the number and location of baffles (I think I see one under the gauge hole), this might be enough to clean the tank well. The cost might be the same as getting a real filter and elements to do it yourself.

Mark

Edit: you posted while I was typing, and I see you have gasoline rated pumps.

 

[colemj]

When these tanks were built the cork on the fuel gauge was covered with shellac which is resistance to gasoline, up until they started putting ethanol and gasoline. So I will put ethanol-free gasoline in the tank and according to both Marine people and people who restore old old cars, coding the cork with super glue is a good idea which I already did.

I don't see how this matters. You should not reuse the old gasket, so what happens to it is inconsequential.

Mark

 

[Cocoa Beach Sailor]

There are a few issues with your plan. First, to run off an outboard tank, you will need to provide for the diesel return. You can't just have the engine intake to the tank. Second, those little in-line filters you are using are completely inadequate. You will need a real filter, and the larger the better. Lastly, as @Jim Legere mentioned, you really need to make sure any pumps you use with gasoline are rated for that.

A polishing service like @shemandr suggests will use pressurized fuel to blast inside the tank. Depending on the number and location of baffles (I think I see one under the gauge hole), this might be enough to clean the tank well. The cost might be the same as getting a real filter and elements to do it yourself.

Mark

Edit: you posted while I was typing, and I see you have gasoline rated pumps.

I don't see how this matters. You should not reuse the old gasket, so what happens to it is inconsequential.

Mark

I am not sure what constitutes a real filter. I will be using 20 micron see-through inline filters. They seem real to me but I might be hallucinating haha. The cork I wrote about is the cork which actuates the fuel level gauge. The gasket is rubber for the gauge itself, which I am reusing as it was in good condition. I have no idea how much a fuel polishing service costs but I am 100% certain that it is a good bit more than half a dozen $7 see through filters.

 

[colemj]

I am not sure what constitutes a real filter. I will be using 20 micron see-through inline filters. They seem real to me but I might be hallucinating haha. The cork I wrote about is the cork which actuates the fuel level gauge. The gasket is rubber for the gauge itself, which I am reusing as it was in good condition. I have no idea how much a fuel polishing service costs but I am 100% certain that it is a good bit more than half a dozen $7 see through filters.

By "real" filter I meant a larger one designed as a primary for an engine. The capacity of an inline filter is so small that you will be changing them out every minute. For what you want to do, I'd take a chance on a $45 large Racor knockoff (then install it on the engine permanently): https://www.amazon.com/Dtomi-Separator-Compatible-Construction-Machinery/dp/B0D148GDGL/ref=sr_1_3?crid=3MBRSTEQTPA7N&dib=eyJ2IjoiMSJ9.yVNRzotwhE9KZ0vr-Wd-QOaxh1CuY0a_0UtJE7F-tS-X_OvrVV8a34GZQHKXLMkt.Tc5HpYhZps5cv5mo-RQnOsyctiwnFRaMCvZqfnzD5EU&dib_tag=se&keywords=turbine+900+fuel+filter&qid=1747247843&s=automotive&sprefix=turbine+900+fuel+filter,automotive,181&sr=1-3

Remove the sender, or at least the cork arm, and you won't have to worry about getting ethanol-free fuel.

Compare the filtering capacity of this to your tiny in-line:

 

[Cocoa Beach Sailor]

I did already take into account needing something for the diesel return. I decided that I am going to seal the tank putting a piece of hose between the fuel pickup and fuel return fittings and leave the 10 gallons of gasoline sit in there for a few days of offshore sailing and then pump it out through these small filters when I am at an anchor. Circulating it through filters isn't really relevant since I'm going to run all of the fuel through a filter when I take it out of the tank. I already reinstalled the fuel gauge and don't feel like taking it out and then putting it back in again so I'll just go with the ethanol free gas. I can always use it for my 19 78 Evinrude 15 horsepower outboard motor as well where ethanol free is definitely the way to go . When I pump the gasoline out I am sure I will go through a number of filters but I don't want to spend $45 for another rancor knockoff and then have to buy expensive elements for it as well.. I bought a brand new one and that is the main filter for the engine and I bypassed the Anmar filter because there's no need to have multiple filters. Having one good big one that is easily dealt with as opposed to the Yanmar with the bolt on the bottom, 3qm30, and the associated extra places to develop leaks isn't worth it to me. I am certain a fuel polishing service is not in budget especially when I can do an entirely sufficient job by pouring gasoline in the tank.

By "real" filter I meant a larger one designed as a primary for an engine. The capacity of an inline filter is so small that you will be changing them out every minute. For what you want to do, I'd take a chance on a $45 large Racor knockoff (then install it on the engine permanently): https://www.amazon.com/Dtomi-Separator-Compatible-Construction-Machinery/dp/B0D148GDGL/ref=sr_1_3?crid=3MBRSTEQTPA7N&dib=eyJ2IjoiMSJ9.yVNRzotwhE9KZ0vr-Wd-QOaxh1CuY0a_0UtJE7F-tS-X_OvrVV8a34GZQHKXLMkt.Tc5HpYhZps5cv5mo-RQnOsyctiwnFRaMCvZqfnzD5EU&dib_tag=se&keywords=turbine+900+fuel+filter&qid=1747247843&s=automotive&sprefix=turbine+900+fuel+filter,automotive,181&sr=1-3

Remove the sender, or at least the cork arm, and you won't have to worry about getting ethanol-free fuel.

Compare the filtering capacity of this to your tiny in-line:

View attachment 231504

 

[Charlie98117]

Seems like you're going through a lot of effort and still won't have a throughly clean tank. I was having issues with filters in rough seas so bit the bullet and installed an access hole and scrubbed it out by hand. The plate was a bit more than I wanted to spend but no more issues and that is important to me.

 

[Cocoa Beach Sailor]

The effort is not that great. I was certain to empty the tank regardless so that is not really an effort to be put on the Ledger of the project of cleaning the tank. Putting in 10 gallons of gasoline is hardly much effort. Taking the gasoline off not so much effort either running it through a filter as I do take it off the tank. The solvent component of gasoline is quite robust. I do believe it will completely clean the tank and it seems like scrubbing It Out by hand and adding an access hole would be a whole lot more effort. Sometime ago when I was in the Keys I allowed some 20 gallons of gasoline to get into my diesel tank. We pumped it all out and replaced it with diesel but I quickly went through three sets of filters when I went out the next day in very moderate seas. Sitting in a calm slip after being at the fuel dock the gasoline had worked its magic in dislodging lots of gunk. I had no more filter problems after that. Getting every bit of the gasoline out will be key

Seems like you're going through a lot of effort and still won't have a throughly clean tank. I was having issues with filters in rough seas so bit the bullet and installed an access hole and scrubbed it out by hand. The plate was a bit more than I wanted to spend but no more issues and that is important to me.

 

[colemj]

Getting every bit of the gasoline out will be key

That's not so important. A small amount of residual gasoline mixed with the diesel won't hurt anything.

Mark

 

[Cocoa Beach Sailor]

That's not so important. A small amount of residual gasoline mixed with the diesel won't hurt anything.

Mark

Yes, I believe the threshold is about 6 or 7%. My concern would be to get all particulates suspended in the gas out, lest they fall out of suspension after the diesel is re introduced