is this normal? i cant tell you how many repairs i've done with the system "under pressure" and mopping up diesel. all i had to do was open the cap. i read a thread somewhere that you shouldn't have pressure in the tank unless you have a clogged vent line? true?

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'92 300D 2.5
'99 E300TD

Sounds like, but I'm not familiar with that engine.

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83 SD

84 CD

If it is in regards to the diesel, the vent is to relieve a negative pressure. In a gasser it is normal.

I think the vent line is dual purpose: relieves both vacuum and over-pressure. I'm not sure what the set-points are, but I've noticed a slight pressure build-up in both my 124 cars after extended driving.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Fuel tank pressure after driving.

This link is for the gasser (107 and 126); if they are the same as the diesels, according to the PDF, the vent allows air in and out of the tank, depending on need.

http://www.peachparts.com/shopforum/attachments/diesel-discussion/100682d1331719150-imploded-fuel-tank-so-sad-47-030.pdf

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

Negative pressure from a clogged vent.

Positive pressure from warming up the air in the tank

__________________
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!

I wouldn't worry about it, just make sure to open the cap if you're doing any work that involves removing fuel lines

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1982 300D Turbodiesel, daily driver. Mods so far: Fram 8038 paper filter, 4 brake light mod, Gen II w126 (front) rotors/calipers, boost turned up to 12lbs, non-egr manifolds, water/methanol injection, 4-speed manual
1980 300SD Turbodiesel, project car, nearly ready to hit the street

1974 240D, New paint

Not very good advise since a badly clogged tank vent can result in a collapsed tank.

On W123 diesels starting 1981, the tank vent is under the car rear driver's side and needs to be cleared on a regular basis. Per FSM, this vent opens at pressures between 0.4 to 0.7 psi and at vacuums of less than 1" HG. I don't know what the spec for the 92 is but I would assume it is similar.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

How is the tank going to collapse if it has pressure in it? I have yet to see a diesel Mercedes that didn't have pressure in the tank when the filler cap was taken off, and we've had six of them and several of my buddies currently have or have had them. These include w115, w116, w123, w124, w126, and w201 models. If anything slight pressure in the tank would just help feed the lift pump

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1982 300D Turbodiesel, daily driver. Mods so far: Fram 8038 paper filter, 4 brake light mod, Gen II w126 (front) rotors/calipers, boost turned up to 12lbs, non-egr manifolds, water/methanol injection, 4-speed manual
1980 300SD Turbodiesel, project car, nearly ready to hit the street

1974 240D, New paint

What happens when a tank vent gets clogged.

Fuel Tank Vent Warning

I had this pressure problem with my 80 240D a couple yrs ago, this is what I did: Copied from a post 2 yrs ago.


I just went through this on a 82 240D a few days ago, had pressure when releasing the fuel cap. removed the vent check valve and the Bell piece. bell open, but blowing through the Vent check was difficult. so reamed the little sucker with a screwdriver. blows good now, both ways


Was it the right thing to do??? IDK, but it still works ok 2 years later..


Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

With a badly clogged tank vent, under certain conditions, the pressure can change to vacuum (i.e. during long trips) and will collapse the tank.

Thanks for the link Charmalu

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

yup. I've seen it several times...

the car just sitting there, will build pressure/vacuum depending on temp inside the tank, and pressure/temp outside the tank...

but when driving, fuel is being removed from the tank, and if no air gets in... the tank sucks flat.

it takes VERY little vacuum to collapse a tank.. 2-3" HG will do it. and the LP can pull lots more than 3"...

__________________
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!

Here is a good one on a rail Tank car.

https://www.youtube.com/watch?v=Zz95_VvTxZM


Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

so, where is this vent line that i need to be checking for clogs?

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'92 300D 2.5
'99 E300TD