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Discussion Starter #1
I had something strange happen while I was attempting to fill my diesel tank... no matter how slow I filled it, it kept overflowing like the tank was full, but it was only 50% full. Is there a valve in the fuel fill line somewhere?? The other thing I thought of was that maybe the fuel tank vent was blocked somehow. Has this happened to anyone?
 

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Your vent is blocked
Maybe baubers
This is common
Use something like weed eater line and work/twist it free from the vent side

Put a bend at the end of the line and snake it in..twist and push
Key is getting it into the vent line.
Try to..feel it, work it
 

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I had something strange happen while I was attempting to fill my diesel tank... no matter how slow I filled it, it kept overflowing like the tank was full, but it was only 50% full.
Was it the normal fuel pump you use? Or did you put in the high pressure pump? Or did the dock guy switch from low to high pressure?

High pressure pumps the fuel can hit the side walls of your hosepipe and create bubbles.

If not that, I'd go with the vents.
 

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Agree it's most likely the vents.

Sometimes you are simply displacing air faster than it can vent. If using a high speed diesel pump, designed for big ship, even going slow can be pretty fast.
 

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When the same thing happened to us the vent line was plugged. Working bits of wire into the vent hole in the cockpit did nothing. I removed the vent hose from the fuel tank (careful, there will be fuel standing in the low spot in the vent line), duct taped the dinghy foot pump hose to the vent line, and jumped on the foot pump. Mud, broken pine needles, and insect parts all soaked with fuel shot out the vent. I flushed the vent line with water, blew it out with the dinghy pump, and put it all back together after threading the hose through a length of PVC pipe to remove the low spot in the hose.

Bill Murdoch
1988 PSC 34
Irish Eyes
 

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Discussion Starter #7
When the same thing happened to us the vent line was plugged. Working bits of wire into the vent hole in the cockpit did nothing. I removed the vent hose from the fuel tank (careful, there will be fuel standing in the low spot in the vent line), duct taped the dinghy foot pump hose to the vent line, and jumped on the foot pump. Mud, broken pine needles, and insect parts all soaked with fuel shot out the vent. I flushed the vent line with water, blew it out with the dinghy pump, and put it all back together after threading the hose through a length of PVC pipe to remove the low spot in the hose.

Bill Murdoch
1988 PSC 34
Irish Eyes
How in the world did *pine needles* get in there?
 

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I don't know but assume that whatever insect built its mud nest in the vent line used them in the construction of its nest. They were not whole just short pieces.
Most vents come with a screen, don't they? Can they be replaced? I have a blocked vent from my holding tank that I need to get to in the spring...
 

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Some holding tank vents include an activated charcoal odour remover in the line. If this gets a blurp of tank contents ???
 

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Nothing so fancy on my boat. The yard owner speculated that the screens sometimes get plugged with wax from overenthusiastic Karate Kids...
 

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Discussion Starter #13
I checked the cockpit end of the vent, it's clear. I decided to follow Bill M's example and disconnect the vent hose at the fuel tank end and use the dinghy foot pump to blow it out. Not surprisingly, it was a lot easier to say it than to do it. I backed both clamps off but I cannot get the vent hose off of the hose barb. Any recommendations for how I could loosen up the end of the hose so I can pull it off? Heat gun or hair dryer maybe?
 

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Heat is always my first thought for stuck hoses, but I’m not so sure around fuel. Diesel will auto ignite around 400 degrees F and a heat gun must get at least that hot. I think I’d avoid.

There is a tool for removing hoses. Looks like a square angled hook. They work great to remove. They often damage the hose.

Here’s a random example.

Drake Off Road 4521 Hose Removal Tool https://www.amazon.com/dp/B0050SFZBG/ref=cm_sw_r_cp_tai_BxJgEbRCWBW48
 
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KB,

How much slack is there in that hose? Seems to me there was plenty. So, if you can't easily get the sucker off, you can just cut the hose off square, then cut the detritus off the inlet fitting, then just slide the fresh end on after you've tested. It's what I did when I replaced our tank.

If you don't have enough slack to cut it off, you can take a large pair of vice-grips and grip the hose at the tank and try to rotate it to break the seal (maybe somebody used a sealant). Don't tighten the vice-grips so much that you might damage the fitting, but just enough to get the teeth of the vice-grip into the rubber. If you damage the rubber, you will only need to cut off as much as the width of the vice-grip jaws. This method has also worked for me in the past. It gives you a lot more leverage than with just your hands.

Dave
 

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Discussion Starter #17
KB,

How much slack is there in that hose? Seems to me there was plenty. So, if you can't easily get the sucker off, you can just cut the hose off square, then cut the detritus off the inlet fitting, then just slide the fresh end on after you've tested. It's what I did when I replaced our tank.

If you don't have enough slack to cut it off, you can take a large pair of vice-grips and grip the hose at the tank and try to rotate it to break the seal (maybe somebody used a sealant). Don't tighten the vice-grips so much that you might damage the fitting, but just enough to get the teeth of the vice-grip into the rubber. If you damage the rubber, you will only need to cut off as much as the width of the vice-grip jaws. This method has also worked for me in the past. It gives you a lot more leverage than with just your hands.

Dave
There's not much slack but is probably zip-tied to other stuff so if I can cut it loose maybe that would help. I'll give the vice-grips method a try, thanks!
 

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Mud daubers are bad for making nests in vent and discharge lines. They nearly sank a power boat I was on, blocking the bilge discharge. Found the plug just in time.
 
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