Which is fuel out and which is fuel return 1985 300SD tank - PeachParts Mercedes-Benz Forum

coachgeo · #1 01-17-2009, 07:04 PM

I did not even know where to start to search for this answer. My appolgies for that.

If anyone has an idea on what key word(s) to search by I'll be happy to.

What Im trying to get answered is... when laying on your back under a 300SD... which fuel line is which? It appears the fuel lines go up from under the car into the tank area on the passenger side.

What line is it on the driver side that goes up into tank/trunk area. Looks to be a valve (or filter?) on it. Im guessing a vacuum line (though its rather large for that) for something like maybe the automtatic antena?

Im not getting fuel to the engine. I have manually (mouth) sucked on the fuel line till I was blue in the face (thru an electric pump) and I get little to nothing. Pump turned on.. (not primed well) cant seem to pump anything up either.

Want to know what line to pull back there and blow thru to see if the tank screen is clogged. Might put an electric pusher pump back there too for a while and by pass an aging OEM lift lift/primer pump. Any cautions/concerns with that idea?

coachgeo · #2 01-17-2009, 07:29 PM

Been searching.

Found a post that said the line I thought might be a vacuum line, IS the fuel out line. I sorta thought so at first but I pulled it apart and no fuel came rushing out. Nothing came out. So either the tank is empty (but showing over a quater) or the screen is completely blocked, or thats not the fuel line.

So which is it

here is thw two pics with the blog. Blog is about replacing tank strainer in an 87SD

Blog says the pic with one fuel lines is fuel out with strainer above it in the tank

Other photo of Two lines going into the tank it says is return and Vent. But on mine the two line side (passenger side) has both lines plumbed. Unfortunately Im just little to big to crawl under the car and follow the lines.

here is the whole blog address

http://biodieselbob.blogspot.com/2008_07_01_archive.html

pics are about half way down the page.

coachgeo · #3 01-17-2009, 08:24 PM

tried searching skinnerbox and it seems not to be working for the 123 or the 126 models

pop & blow · #4 01-17-2009, 09:10 PM

well the one with the cigar hose is the return line, the other line is the fuel pressure line, you could blow from front to back and see if that clears your problem. , you do have a vent line at the tank one return line and one fuel line. if it,s not pulling fuel from the tank the screen is stoped up at the fuel line in the tank

coachgeo · #5 01-17-2009, 09:45 PM

Quote:

Originally Posted by pop & blow

well the one with the cigar hose is the return line, the other line is the fuel pressure line, you could blow from front to back and see if that clears your problem. , you do have a vent line at the tank one return line and one fuel line. if it,s not pulling fuel from the tank the screen is stoped up at the fuel line in the tank

sorry, thought I was clear in my question. I am asking about the FUEL TANK. Fuel lines at the rear, on the bottom deck of of the car.... where they go up into the fuel tank.

Under the hood I am well aware of which is the return and which is the fuel feed line.

Thanks for trying.

Palangi · #6 01-17-2009, 09:50 PM

If it's the same as a 123, the line with the threaded fitting is the fuel feed line, and the one fastened with just a hose clamp is the return line. The feed line should be threaded into the strainer, which is, I think, about a 46 mm hex.

coachgeo · #7 01-17-2009, 09:57 PM

UPDATE

Got pictures to work.

Thanks Palangi, I will clean things up back there and look closer to see if one has a threaded feed line. I do not recall seeing one. Both looked to be hose with clamp style. In fact all three (two on one side and third on the other) looked to be hose and clamp style.

Palangi · #8 01-17-2009, 10:02 PM

Quote:

Originally Posted by coachgeo

UPDATE

Got pictures to work.

Thanks Palangi, I will clean things up back there and look closer to see if one has a threaded feed line. I do not recall seeing one. Both looked to be hose with clamp style. In fact all three (two on one side and third on the other) looked to be hose and clamp style.

It could be that some shade tree has replaced the original feed hose (which was a hose with a crimped-on threaded fitting) with a piece of bulk hose secured by a hose clamp. Regardless, the one that goes into the big hex part would be the fuel feed line.

coachgeo · #9 01-17-2009, 10:34 PM

is the hex typically covered by a rubber boot or anything or is it exposed? Like the pics above I do have the one line side.. w/a rubber boot. But there is also a small plastic piece there in the fuel line. It could be a tiny inline right angle fuel filter but is sure looks real small for that.

And you know..... now that I think about it.... that line may well be a fitted line. I payed attention to the little dodad filter/vacuum valve looking thing that is put inline with it. It had hose clamps, while the line going up to the rubber boot... hmmmmm.... it might well have been a fitted line.

will find out tommoror. Car is a 20 min. walk from where Im at.

Yet Im still confused. All three lines are plumbed to steel lines. If one is a vent.... wouldnt it ... vent like the one in the photo.

Palangi · #10 01-17-2009, 10:40 PM

I have never been under a 126, but on a 123 the 46 mm hex fuel strainer is not covered up. It is exposed where you can get a socket on it after you remove the threaded fitting. I don't remember the size of the threaded hose fitting, probably about 14 to 17 mm.

coachgeo · #11 01-17-2009, 11:10 PM

so anyone else? Someone who knows the look of the fuel lines at the tank on the 85 300SD, got more info to share?

look forward to your responce. My searches are running dry. Really sad to see the Skinnerbox no longer working.

coachgeo · #12 01-17-2009, 11:57 PM

ok.... did some more searching.

for 1985 300SD the enclosed picture is the fuel tank VENT. This is apparently the single line on the drivers side. This is the gizmo whatumacallit I mentioned earlier. After some reading and google pic searches I came across this. Made me curious so I searched further by searching parts catalog.

Another thread points out that this is plumbed to steel line that heads over by the rear wheel suspension somewhere where it then vents to atmosphere.

coachgeo · #13 01-18-2009, 01:50 PM

0k I'm out at the car w/lap top and cellular net service. Got car up on jackstands.

Will report back to see what folk say and to add updates

coachgeo · #14 01-18-2009, 04:56 PM

85 SD is nothing like 87

Thank you to those that pointed out that the fuel out would be the one that is out of fuel strainer, and of course.. reminder what the fuel strainer one would look like.

mainly though..... it was out of fuel. retistered 1/4 tank but bone dry.

suspected that cause I had manually sucked the fuel line up at the engine enough to pull up fuel. Check valve was in place so I could breath between.

opened fuel cap and got a wush.... so I new I had sucked good thus nothing must be in the tank.

When I pulled the line from bottom of the tank

sure enough... no fuel.

Put some in (brought a 5 gal can along) and pulled line. Whala.. fuel.

There was a suspect hand primer pump and or lift pump issue soo I had an electric on hand with me.

Installed it right by the tank. Used it to prime the system.

Car.... with a jump... started and is still running. No unusual leaks.

Success.

Palangi · #15 01-18-2009, 06:34 PM

Good show! You got it running, and you didn't get a diesel bath in the process!