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  #16  
Old 02-27-2009, 09:37 AM
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I am sure there is a vent, which will relieve vacuum or pressure. I'm not certain where the vent is located. Usually it's a tube/hose on the bottom of the tank. Odd that all 3 of your diesels have the same problem. Can you describe what happens when you have a full tank and you open the filler cap? Does fuel get pushed out of there?
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Originally Posted by LuckyEddie View Post
Are you sure?? I have three of them 84 300sd, 85 300sd, and 84 300cd and they all keep pressure in the tank even for days. There is a check valve on the side of the tank but I thought that it was to keep from having a vacuum. It is aggravating at times when the pressure will bust a return line and leak for several days if the tank is half full.

Where is the little sucker and how do I fix it??

Thanks for pointing that out I thought that they were like that.
Robert
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  #17  
Old 02-27-2009, 10:00 AM
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95 e300d

My tank also holds pressure. The vent is primarily for relieving vacuum, but it will release with enough pressure. However, it takes a lot of pressure before the valve activates, still its less than the tank cap obviously.
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  #18  
Old 02-27-2009, 10:02 AM
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Quote:
Originally Posted by LuckyEddie View Post

Where is the little sucker and how do I fix it??
On the SD, the vent is in the driver's side rear fenderwell. It's a tube that gets clogged with debris..........you'll need some piano wire to clear it.
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  #19  
Old 02-27-2009, 10:33 AM
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Interesting. So the vent on these diesels IS a check valve to let air in the tank only? Why is there so much pressure in Roberts cars, to the point of popping a return hose? Where is the pressure coming from? While driving, i'd think the vacuum created from fuel usage is greater than whatever pressure is created from fuel being returned to tank?

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Originally Posted by connerm View Post
My tank also holds pressure. The vent is primarily for relieving vacuum, but it will release with enough pressure. However, it takes a lot of pressure before the valve activates, still its less than the tank cap obviously.
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  #20  
Old 02-27-2009, 12:14 PM
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Question

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Originally Posted by funola View Post
Interesting. So the vent on these diesels IS a check valve to let air in the tank only? Why is there so much pressure in Roberts cars, to the point of popping a return hose? Where is the pressure coming from? While driving, i'd think the vacuum created from fuel usage is greater than whatever pressure is created from fuel being returned to tank?

I would have thought that if the vent was plugged up the tank would have a vacuum in it but it has about 2- 3 psi (WAG) and they all seem to be the same. More when fuel is low, more room for air? Has anyone else noticed this?? I just opened a tank that had been sitting for two weeks and it still had pressure in it. Is there a vapor recovery system on these? Vapor recovery was mandated in the early seventies but what about a diesel?? I will try to find the vent in the passenger well and see if it is clear. I read somewhere that there was a check valve on something under there.

I got the picture from another thread. Is this the check valve? and the line to be cleaned out?? In both directions or just to the tank.


Another wild thought that I would like to run buy you guys ----

If you reverse the return and suction lines in the engine bay will the returning warm fuel, forced back through the strainer, clean the strainer enough to get a sick car home? Remember that it will run out of fuel at about half a tank (level of return pipe in tank).
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tips on changing fuel filter?-vent.jpg  

Last edited by LuckyEddie; 02-27-2009 at 12:25 PM.
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  #21  
Old 03-01-2009, 12:25 PM
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I just checked my two Dodge diesels and both of them keep some pressure in their tanks also so it might be just a normal part of the fuel vapor recovery system.
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  #22  
Old 03-01-2009, 02:05 PM
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Under the car's tank there are 3 rubber hoses, a supply, return, and vent hose. When the vent hose for the tank is plugged, and you open the fuel cap to put more fuel in the tank, you hear a "whoosh" and you need to replace the vent hose under the car. IIRC, if this is hose plugged enough it will cause fuel starvation issues.
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  #23  
Old 03-01-2009, 04:27 PM
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Thanks I will look as soon as the weather will let me. What part do I need to replace?? What plugs up in the system??

Thanks
Robert


Quote:
Originally Posted by derburger View Post
Under the car's tank there are 3 rubber hoses, a supply, return, and vent hose. When the vent hose for the tank is plugged, and you open the fuel cap to put more fuel in the tank, you hear a "whoosh" and you need to replace the vent hose under the car. IIRC, if this is hose plugged enough it will cause fuel starvation issues.
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  #24  
Old 03-01-2009, 05:50 PM
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I just changed my filters, and it's a 22mm on mine.
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