true, but if you have a very low tank, there would not be much fuel to warm, and the air in the tank would be the majority of the volume there, if it started out fridgid, then you opened the tank when the temps hit 70, I can see 50°F temp diff making quite a pressure diff...
that's the reason I am choosing...

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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!

Well, as soon as I get my other cars injectors changed and out of the garage I'll put this one on the ramps and have a look see at the vent line. I'll try blowing air up there too.
I am glad to have the manual on cd but the pictures are worse than crap and I can't find anything in them on this.

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Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

Daw_Two,

'Depending on your model there may be a one way valve in the vent line.

I know the 124.128's do have the vent valve.

AL,

My tank is infested with Starbrite's Startron Diesel Fuel Enzyme (Algae eater).


I kinda like VSTECH's proposal.(Kinda the reverse,But when you leave a Petrol
container [Red Plastic] out on a cool night after a warm day the container
"Vacuums" in on itself [forced by the superior ambient air pressure outside]
by Morning.)

Model is 84 300SD low miles very good condition but mystery past.
I am thinking that if I had an algae problem it would probably show a bit in the prefilter(which is clear) and it probably wouldn't pull well at high rpm. I opened her up a few days ago and got 175 KPH... about 108 or 109 mph. And was running speeds around 130 to 150 for more than an hour before I let her all the way out.
I assure you she was running very sweet at those rpms or I never would have gone there (and conditions were ideal regarding road and traffic).
So anyway I have the new style primer pump on the way, hoping that will stop the leaking in of air and that will solve the problem but will either know in a few days or be able to check it off the possibles.

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Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

w126 1986 300SDL --- okay, let's assume a one way vent valve. Which way? Yes, it matters to me to know. If it is one way IN, then the tank could build pressure. If the value is one way OUT, then the tank could have a vacumm. RIGHT?

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daw_two
Germantown, TN

Links:
Sold last car --- 05/2012 1984 300D Light Ivory, Red interior
Cluster Needles Paint
New Old Stock (NOS) parts

Past:
3/2008 1986 300SDL "Coda"
04/2010 1965 190D(c) "Ben"
& many more

Yes, your car has a check valve, one way out. The file is too large to download, I can send another way, PM me.

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83 SD

84 CD

had a spring and rubber check valve. After one too many 'puffs and sucks' I crawled underneath and took it off. I could only slightly blow through and NOT suck through at all.

Not sure about the 123 but 124's are sort of bell shaped and have a small fitting to go into the hose. I "FIXED" the check valve with a small drill bit, put it all back in place and now I'm worried that somehow dust will find its way into the fuel. But, hey, at least the tank isn't huffing and puffing when I take the cap off now.

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1987 300D (230,000 mi on a #14 head-watching the temp gauge and keeping the ghost in the machine)
Raleigh NC - Home of deep fried sushi!

The car that has this problem now is a 126 (300SD). When I get the W123 back together I will get it in the shop and see if I can 'fix' it too
While I want the fuel clean I think I can trust the two filters, I don't generally drive much gravel or ford a lot of streams anyway

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Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

for the 124.128 the shop manual says if the system is operating properly there will be 50mbar pressure in the tank.Should the valve in the vent fail the valve in the fuel tank cap will release the pressure at 300mbar. I wouldnt go drilling holes in anything,that pressure is intended by design to be there. My $.02 Don

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Red Green "This is only temporary,Unless it works!"

97 E300D 157000 miles
87 300TD ?141k? miles

Thanx, I have come to this realization too. I see that the valve actually has a restriction each way (in & out) but for different pressures(and purposes). I think now that my low power at low and mid rpms is perhaps a by product of the air leak I have at the hand pump. (new one en route). we'll see

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Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

Thanx for the file.
I understand this much better now.

__________________
Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

oldiesel,

Thank You! I can see the vent valve in the RU schematics website(still can't
find some things in the FSM,no matter how hard I bang my thumb with a ball
peen hammer)

So, The engineers in Sindelfingen were setting up the system to relieve excess
fuel pressure two ways:Overpressure less than 300mb, but greater than 50mb
is relieved by the fuel tank vent line valve.Overpressure above 300mb is
relieved by the fuel tank cap (this would have been their catastrophic prevention fall-back if the valve in the vent line failed in the closed position).

Thinking about it, now that I understand,any sort of vacuum in the Tank would
fight the lift pump's job of delivering the fuel to the Injection Pump.
If the system is properly functioning, it cannot develop a vacuum in the tank...BUT will always tend to be slightly pressurized.

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'84 300SD sold
124.128

Normally no harm on our old diesels. Beware on a gas car though. If high enough the customer can complain of bad gas milage on a carbed car. Guess it just forces the needle off the seat. Seen it on older japanese cars when they were newer.

From a file sent by Toomany MBZ, I better understand that a little pressure is normal. As a side note I did get that old style (leaking air) primer pump replaced and the car is (I think) running much better now. It had been sucking air in the base of the old primer pump(no sealing washer)and I could see it percolating up the clear fuel line to the second filter.

__________________
Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR