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  #1  
Old 08-08-2011, 06:27 PM
boneheaddoctor's Avatar
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What happens when a tank vent gets clogged.

What happens when a tank vent gets clogged on a W123.


For anyone that doesn't think the lift pump on a OM617 can practically suck a golf ball through a garden hose....here are two pictures of my fuel tank when the vent became fully blocked for some reason on a 3,200 mile round trip.

Two points of note.....the car never experienced a power loss, and it ran 80-90 mph during all of this. Right up until the fuel gauge suddenly stopped functioning with the only symptoms of a reduced fill-up volume. I drove the car another 4 hours after it crushed down this small, at this point it could only hold 6 gallons of fuel at most.


I guess these pictures are sized too big so you have to click the thumbnails for a better look.
Attached Thumbnails
What happens when a tank vent gets clogged.-p7020791.jpg   What happens when a tank vent gets clogged.-p7020792.jpg  
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Old 08-08-2011, 07:12 PM
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Did it make a noise at all?
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Old 08-08-2011, 07:15 PM
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Holy hell! I better fix my vent soon
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Old 08-08-2011, 07:28 PM
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Quote:
Originally Posted by TheDon View Post
Did it make a noise at all?
No...no noise....nothing..... I was driving from Virginia to central North Dakota. Noticed through Minnesota the fill-ups were less than I expected....when I got to Fargo I should have had enough fuel to make it to my destination....and went from 1/2 tank to empty from the south side of town to the west side, pulled over expecting to see fuel pouring out and nothing....Had a fuel in the trunk and 4 gallons and it was to the top of the neck. So I got back on the highway and ran 80-90mph the next almost 300 miles. Got where I was going and it stalled, but restarted right up, but ran rough the last mile. Saw it crushed when I pulled the panel off...so I put 120 psi on a blow gun. wrapped a rag around it and jammed it into the fuel filler, popped the tank out......then hooked a hose up to the vent tube and after a moment heard something pop into the tank....then the vent was clear. Gauge still read empty....and expected something to read....emptied the remaining gallon of the one can, and emptied the second 5 gallon can, that brought the gauge up to 1/4. Next day took it to the station and put another 15 gallons into it.....so it was sucking air when it started running rough. It presented no symptoms on power, acceleration or smoothness until it was empty and sucking air as would be expected at THAT point. Only some suction at the cap.

No further events on the return trip....averaged 31 mpg based on the fuel receipts over 3,200 miles of the trip. And my Odometer and speedometer are almost spot on with the tires and gears I'm running.

And I hit the 200,000 mile point passing Cleveland, OH on the return trip.
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1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche
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Old 08-08-2011, 07:33 PM
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Quote:
Originally Posted by Iheartboost View Post
Holy hell! I better fix my vent soon
There is still a crease in drivers side of the tank but it popped back out to full capacity.

Didn't take a picture after I popped it back out.

It almost pulled the filler cap THROUGH the quarter panel at that point.

Not likely to happen on short trips....but I was running hard non-stop from fill up to fill up on the highway..no time for the vacuum to equalize from any imperfect seal. But I did stop for food and restroom breaks before hitting pumps for fuel....so it didn't seem as bad when I did pull the cap off than it would have immediately after getting off the highway.
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1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
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---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche
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Old 08-08-2011, 08:35 PM
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Just as I suspected.... Minn. sucks.
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Old 08-08-2011, 08:53 PM
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That's frickin amazing ........
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Old 08-08-2011, 09:06 PM
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I decided to post those since there was a discussion recently about what a OM617 lift pump could and couldn't do....didn't remember which thread that was so made my own.

No hearsay here....happened to me in my own car recently...like a month ago.
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1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
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---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche
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Old 08-08-2011, 09:13 PM
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Jesus. Thats impressive.
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  #10  
Old 08-08-2011, 09:42 PM
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Any mechanically driven lift pump will collapse a tank if the vent is plugged. A Bosch VE pump with its internal lift pump (vane type) will also collapse a tank with a plugged vent. Ask me how I know.
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Old 08-08-2011, 09:46 PM
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Wow....talk about the unexpected.


Can I assume that my tank also has a vent that I should go take a look at just to be safe?
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Old 08-08-2011, 10:27 PM
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That is one tough lift pump you have !!! Sick ones would not pull the skin off custard.
I guess though that the low pressure was all the way around the fuel system so it was your IP high pressure elements doing the work.

I have seen fuel tanks expanded a little with air pressure to increase their capacity. You are lucky it didnt go bang !!
As a kid we once piped up 150 # to a 50 gal drum for fun. We ended up with 3 sheets of flat steel & a hole in the shed wall. Lucky we were not hurt. Our ears were ringing for a few days & our backsides were sore after dad found out what we had done !!!
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Old 08-08-2011, 10:27 PM
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it's actually amazing how little vacuum it takes for the atmosphere to crush a steel can.
8 to 10 inches of vacuum should be enough to allow that flat long tank. I should put a gauge on one of mine, and measure how much vacuum it takes to collapse it.
heck, I ought to video the procedure...
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  #14  
Old 08-08-2011, 10:29 PM
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Quote:
Originally Posted by vstech View Post
it's actually amazing how little vacuum it takes for the atmosphere to crush a steel can.
8 to 10 inches of vacuum should be enough to allow that flat long tank. I should put a gauge on one of mine, and measure how much vacuum it takes to collapse it.
heck, I ought to video the procedure...
Please do!
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  #15  
Old 08-08-2011, 10:29 PM
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Quote:
Originally Posted by layback40 View Post
That is one tough lift pump you have !!! Sick ones would not pull the skin off custard.
I guess though that the low pressure was all the way around the fuel system so it was your IP high pressure elements doing the work.

I have seen fuel tanks expanded a little with air pressure to increase their capacity. You are lucky it didnt go bang !!
As a kid we once piped up 150 # to a 50 gal drum for fun. We ended up with 3 sheets of flat steel & a hole in the shed wall. Lucky we were not hurt. Our ears were ringing for a few days & our backsides were sore after dad found out what we had done !!!
... 3 sheets?
lid one, lid two, and the barrel itself?
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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