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Date Posted: - Friday - 07/ 4/08 - 2:44am
Author: Tom Burke
Subject: Diesel in the Bilge

With great pleasure I welcomed Journey, my M31 to her new port in Blaine, Washington. I had her trucked up from Dana Point. When she arrived, my rigger talked me into fixing up the masts before re-rigging. We launched her, w/o masts, and I motored her to her new slip. On arriving, I found that the bilge was full of diesel. Later, I found that the truck bed had been saturated with diesel about half way up. My preliminary investigation, after cleaning up the diesel, has been to check the tank. The sides are dry but the entrie bottom of the tank is coated with it. I checked the hose leading out of the tank, to the engine, and that appears completely dry.

The week of July 4th seems an appropriate time for further inquiry into the matter. Any one have thoughts? Might this be simple sloshing about while in transit? A ray of hope would be appreciated.

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[> Pressurize the tank -- Capt'n Mike "Gypsy Mariner" TM36K, - Friday - 07/ 4/08 - 10:35am

To check for a leak in the tank try pressurizing the fuel tank by pumping air into the tank and see if it will hold some light air pressure. You are going to have to close off the diesel fill hose and the other entry/exit fittings. Brush on a little soapy water around the inspection port, the return line fittings, etc. to make sure they are not leaking air and apply air pressure. If it has a leak it won't hold the pressure.

You said the engine ran - but there could still be a leak somewhere on the engine as well. Before you go through the trouble of checking the tank, you may want to run the engine and check the diesel return line from the tank to the engine. Also check the high pressure lines where they enter the fuel injectors - we often loosen these to bleed the 4-108. I've forgotten to re-tighten one more that a few times and got diesel dumped into the bilge. Check around the filters too and the bleed screws.

As for the diesel on the bed of the truck - perhaps you left the power on to the bildge pump and it pumped some of the bilge water/diesel onto the bed of the truck.

I would recommend that you check for leaks around one of the injector high pressure lines first (where the fitting is at the injector) - before you do anything else. Put some paper towels around them and run the engine for a 30 seconds to a minute - if there is a leak it will quickly saturate the towel.

Hope this helps. Good luck. I envy you. There is no better way to spend a 4th of July Weekend then working on an old boat and a 4-108!

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[> [> Forgot to mention -- Capt'n Mike, - Friday - 07/ 4/08 - 10:48am

To pressurize the tank right you really should pump out the diesel in your tank and put it into some Jerry cans. Plus, if you enlarge a hole in the tank during the process - you'll have less of a mess to clean up and have saved yourself some expensive diesel fuel.

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[> [> diesel leak -- Steve M-32 #59, - Friday - 07/ 4/08 - 11:30am

First off, welcome to Puget Sound. It's always great to see another Mariner up here. As far as the fuel goes I'd agree with Cap'n Mike that you might have left the bilge pump on which resulted in the fuel on the truck bed. However, if the bottom of the tank is wet I wouldn't worry about the engine leaking too much (unless the engine is just as wet as the tank). Since the tank is so much higher than the engine I can't conceive of a way for an engine leak to soak the bottom but leave the front of the tank dry. Otherwise what he said aabout the pressure test is spot on. Something to consider, I don't think I would reapir that tank. Yours' is mild steel I believe and is probably at the end of its' service life. Rnadall has an excellent article on putting a new tank into an M-31. Good luck.

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[> [> [> Diesel saok on botton of tank -- Capt'n Mike, - Friday - 07/ 4/08 - 12:07pm

My thoughts on a possible engine leak was that it leaked only when he ran the engine to get the boat to the transport truck and, later, to his slip. The diesel from the engine leaked spilled to the bilge and it soaked the bottom of the tank because that is where the water level was in the bilge and the diesel floated on top of the bilge water.
Capt'n Mike

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[> [> [> [> Bilge level -- Steve M-3259, - Saturday - 07/ 5/08 - 9:33am

I hear ya, but the location of the fuel tank on the 31/32 is right under the cockpit sole and if the bilge level was that high he'd have diesel rings around the cabin interior also. The engine on my boat before I bought it had blown and dumped lots of oil/water in the bilge all the way up to the level of the floor boards. That was still at least a foot below the level of the fuel tank bottom. I just think he would have noticed that much water/fuel inside the hull ;-)

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[> [> [> [> [> Tank location -- Capt'n Mike, - Saturday - 07/ 5/08 - 10:52am

Thanks Steve. I understand what you're saying now. I thought the fuel tank was down in the bilge below the engine. That's where it is on my 36.

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[> [> [> [> [> [> Diesel in the Bilge -- Tom Burke, - Monday - 07/ 7/08 - 10:59pm

My thanks for the advise. I spent most of the weekend soaking up all the diesel and repairing the connecting wire to the float; the wire I broke as I was sponging it all up. The diesel all spilled out, every drop. It was leaking both before and after I had used the engine. The advise all seems to favor, first things first, having the tank pressure checked. Many thanks.
With all that done, sitting on deck, enjoying having her here, well, there is simply nothing so marvelous as just messing around on a Mariner.

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[> Some other thoughts -- Randall, Murre, M31, - Monday - 07/ 7/08 - 11:00pm

Wow. What a stumper. Here are a couple thoughts based on my experience.

On either climbing or descending a grade, your trucker would likely have inadvertently pushed your diesel in the bilge up against the bilge pump float, triggering it, and pumping some out, but on returning to the level the float would have disengaged. In fact, this could have emptied the bilge if the hill was even moderate in length, so does the fact that a lot remained in the bilge when you received the boat imply that the leak is not minor?

If the fuel leak plus any water had filled the bilge right to the level of the propeller shaft, and if the engine was then run and the propeller engaged, the shaft would toss fuel all over the underside of the tank. Iíve had this happen with sea water when my stern gland needs tightening.

Do you have the original mild steel tank? If so, is it possible that all this fuel on the tankís underside is masking the leak? The most vulnerable area is inside the tank--the forward lower edge where water will gather and rust the tank from the inside. If possible, Iíd dry off the outside of this edge and see what accumulates. Vulnerable areas on the outside of the tank are the outer edges where the tank rests on the hull. Salt water can accumulate there with other gunk and accelerate deterioration.

Iíve had the following minor leaks:
-When I installed a new racor primary filter, I had a tough time getting the connections tight enough and they dripped for a while. You checked the out-to-engine hose. Did you check the primary filter connections?
-I had a diesel leak on the engine right at the throttle assembly (port side of my Perkins near the top). Had to replace the assembly, but that cured it. Importantly, this leak only occurred when the engine was running. Iíd suggest running the engine IN GEAR, grab a flashlight, and give a look at the throttle assembly and all the other on-engine connections.

Have you checked the vent line (starboard aft corner on my tank)? Mineís made of copper, much corroded. If the tank was at all full, sloshing on the truck or motoring in a good seaway could have easily pumped quite a bit into the bilge if the line is severed or broken.

Very interested to hear what you learnÖ


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[> [> Diesel in the Bilge -- Tom Burke, - Thursday - 07/17/08 - 9:58am

This is a real possibility. When thinking about the possibilities, I have only thought of a boat, rather level, pounding while the truck is going down the road. However, this began about a day after leaving southern Calif. That would be when he went over the Grapevine outside of LA or, depending on how far he drove on day one, when he headed up the grade leaving California to Oregon. The tank will be pressurized this week. I'll let you know. Much thanks.

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[> [> Desiel problem concovered -- Tom Burke, - Sunday - 07/27/08 - 7:34pm

Having had the tank pressurized, there is a leak in the seam. It is a relatively new tank but of the same size as the original so there are the same problems in taking it out. My current thought is to not repeat building a problem into the boat. Rather, I am thinking of having it cut out and the tank replaced with one that will slip into the space. All calculations seem to mean that will be a smaller tank. On balance, a smaller tank in trade for a smaller problem seems a good choice.

My thanks for all the thoughts.

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[> [> [> original tank -- Randall, - Sunday - 07/27/08 - 10:53pm


If your tank actually is the original size (and assuming your original is the same size as my original), then it should slide out.

See my project article on the MOA board.

After removing the cockpit well sole and after removing the tank brace on the starboard side, slide the tank amidships and lift straight up. Now don't that sound easy? :)

Good luck.


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[> [> [> [> taking out the tank -- Tom Burke, - Monday - 07/28/08 - 12:05am

That still sounds like we have to cut out the cockpit and then rebuild it. I will, however, read your project.

My thanks,


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[> [> [> [> [> correct -- Randall, - Monday - 07/28/08 - 12:44am

Sorry if that wasn't clear.

But that may be easier than cutting the old one out and inserting a smaller tank with out touching the cockpit.

Easy for me to say!

Here's a serious question for you and the board: can a welded tank (whatever metal) that's got a leak at the seam and that ISN'T corroded from the inside, as the old ones are, be fixed? Or is it always just kill it and move on?


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[> [> [> [> [> [> suggested solution -- Tom Burke, - Tuesday - 07/29/08 - 1:58pm

I have availability to many who could weld aluminum but not sure if that is a viable solution. My yard is suggesting a put a 30 gal tank on the port side and leave the problem tank in there. That would add about 260 lbs when the tank is filled. The water tank is on the starboard side so this might balance. I can do that job for about $300. Thoughts? and my many thanks for your inputs.

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