curious diesel leak

HerbertFriedman

Member III
Add me to the list. The identical thing happened to me. I had to re-seal the gauge sender. The problem had not shown up until I topped off the tank and gave the boat a hard sail.
Alan and John, thanks for the information. Question, did either of you find that the sheet metal screws securing the fuel gauge flange (and gasket) were loose, mine were not. That still does not mean that the gasket has not failed and rather than pull the tank (uggh) or replace all the rubber hoses (fill, overflow and return), changing the gasket sounds like an easy thing to try. What kind if gasket material did either of you use? Rubber or cork-like? and did you have to remove the "float mechanism" in order the change the gasket?

From Loren's comment, sounds like I should also replace the rubber hoses, they are 35 years old? I probably will wait for haulout time for that, not sure I can squeeze into those tight places to change the hoses, sounds like a yard job, $$$, uggh.
 

Alan Gomes

Contributing Partner
Alan and John, thanks for the information. Question, did either of you find that the sheet metal screws securing the fuel gauge flange (and gasket) were loose, mine were not. That still does not mean that the gasket has not failed and rather than pull the tank (uggh) or replace all the rubber hoses (fill, overflow and return), changing the gasket sounds like an easy thing to try. What kind if gasket material did either of you use? Rubber or cork-like? and did you have to remove the "float mechanism" in order the change the gasket?

From Loren's comment, sounds like I should also replace the rubber hoses, they are 35 years old? I probably will wait for haulout time for that, not sure I can squeeze into those tight places to change the hoses, sounds like a yard job, $$$, uggh.
No, the screws were not loose. It was just a bad seal with the rubber gasket that was in there.

I got a sheet of cork and cut out a gasket from it. I also used a liberal amount of Permatex on both sides.
 

HerbertFriedman

Member III
No, the screws were not loose. It was just a bad seal with the rubber gasket that was in there.

I got a sheet of cork and cut out a gasket from it. I also used a liberal amount of Permatex on both sides.
super, thanks. I assume you had to pull out the float mechanism that measures the fuel level, any problems there?
 

HerbertFriedman

Member III
I think I found the leak in my fuel system, a busted hose clamp on the engine side of the return fuel hose, please see the attached photo. I was able to get an absorbent towel all around the bottom perimeter of the tank, hoping against hope that I would NOT find a leak. Replacing the tank was bound to cost $$$. No leak. All the hose clamps at the tank and fill port were tight and no sign of a leak there. The screws on the fuel gauge were all tight and no leak in the gasket was evident.

But going back to check the engine, I did find that the diaper under the front of the engine was soaking wet. Looked for leaks at the three fuel injectors and all those hose clamps, nothing, but when I did try to tighten the hose clamp on the red rubber return hose, the screw turned without tightening, Humm? Tugging on that hose clamp, it rotated easily and revealed the break in the band. Replaced the clamp and the diaper, and a day later, the leak disappeared.

Earlier, I did run the engine for 30 mins with the prop in gear, no leaks and no fuel on a new diaper. My theory is that when the engine is running, return fuel is carried by the red rubber pipe back to the tank but there is little or no pressure in the hose because the tank is vented and the rubber pipe was tight enough, even with the broken hose clamp, to prevent a leak. But when I overfilled the tank, both the fill pipe and overflow pipe were filled and some small pressure was built up in the return pipe due to the small elevation of the fill pipe, so that caused a leak in the return pipe??

Thanks for all your suggestions, shoulda tried the obvious first.
 

Attachments

  • busted hose clamp, fuel return hose.JPG
    busted hose clamp, fuel return hose.JPG
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Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
Happened to me. There is indeed pressure in the return line. Mine was cracked recently and sent quite a spray out.

You solved it. I begin to think that the return line is the first place to check when red stains appear under the engine.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Interesting! I recently found and fixed a small but puzzling fuel leak that appeared under one end of our tank. I really did not... want to remove the tank and look for a possible pin hole leak at the bottom seam. The leak seemed to appear and then not appear for weeks. Never much fuel accumulated. This started sometime last year.
Finally I looked really.....closely at the return line fitting with the hose clamp on it. And felt around with a paper towel. Noticed a nick in the hose where I had reattached it years before and that little cut was leaking out occasional drops of diesel that dripped down on top of the bottom fuel exit fitting and then down another inch onto the boat bottom. Removed return hose, cut off an inch, reattached. No further leak.

It's great to solve a problem. Greater still not to have created it in the first place. :(
 
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HerbertFriedman

Member III
interesting to hear that so many people have has problems with that return line.

I am still confused by the notion of pressure in that return line. If the tank is vented and the return line enters the tank near or at the top, then the only pressure in the line comes from the friction of the fuel as it travels through the line back to the tank. That has to be small. My thought was that when overfilling the tank (and catching the fuel from the overflow in a bucket hung over the transom), there could be some pressure in the return line due the height of the fuel in the fill line. But if some actually saw fuel spurting out at the tank end of the return line, there must be another source of pressure, possibly from the fuel pump or the injector pump.
 

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
Return lines popping off was a common complaint on car forums when I read up on this a while back. General sense was that return line fluid flow was low, but pressure can be high.

It would be easy to observe the return line pressure and volume just by pulling the return line off the engine. I'll bet we'd be surprised at the squirt, given what I saw squirting from this crack.

fuel return hose.JPG

I know only experience, and not much of that. Another reason to take a diesel course. Random note: my files show a useful description of fuel injectors, PDF pages 68-70 of a Westerbeke download, here. They're high pressure devices.
 
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Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Perhaps worth noting/remembering is that diesel fuel is a really 'thin' liquid. It will find and exit thru a pin hole or crack that is well nigh invisible to the average naked eye. That, plus any slight pressure at all, makes it a really talented "liquid escape artist" !
:)
 

HerbertFriedman

Member III
I understand about the viscosity of diesel and also that for the "engine end" of the return line, the rubber is fitted onto the pipe whereas for the "tank end" the metal pipe is fitted into the rubber. This makes the leak at the tank end more likely if a hose clamp is not tight.

But the issue I still do not understand is that probably the high pressure in the line is fed by the pressure of the fuel pump or fuel injector pump, but at the tank end, the pressure has to be just atmospheric since the tank is vented. That's quite a pressure gradient.
 

Kenneth K

1985 32-3, Puget Sound
Blogs Author
But the issue I still do not understand is that probably the high pressure in the line is fed by the pressure of the fuel pump or fuel injector pump, but at the tank end, the pressure has to be just atmospheric since the tank is vented. That's quite a pressure gradient.
The pressure in the return line is positive, but something less than that of the electric lift pump. The return line is pressurized, and active, when the lift pump is on, engine running or not.

Like a garden hose that exits into ambient air, the stream is still under pressure until it leaves the hose.
 
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