Primer pump - need fitting type/size - PeachParts Mercedes-Benz Forum

deezulmark · #1 07-11-2008, 11:48 AM

Have a '85 300TD. Looking at the fitting that comes off the fuel primer pump. Anybody know the official type and size of this fitting? Looks like it takes a 22mm wrench. It has a hose barb, I think 1/4", for the short line to the fuel filter. I need to find the same fitting with a 3/8" barb if possible for some mods I'm doing.

Thanks! PM me or reply to the tread.

Mark

whunter · #2 07-11-2008, 12:10 PM

Confused by your question/possible MOD.

The current pump and fitting passes many times maximum fuel capacity of the injection pump.
This is part of why there is a fuel return line to the diesel tank.

Diesel911 · #3 07-11-2008, 12:33 PM

I replaced my plastic line comming from that fitting with a rubber hose and it was 1/4" just as you said. The barb in not attatched to the 22mm part it is a seperate fitting that has angled sides and seals somewhat lik your injector lines (and is about about 5/8 inch in diameter). If you want to turn this into a 3/8" barb you will need to make one or have some one else make one for you.
If your goal is to be able to increase the flow by using a larger hose you will need to look down inside at the fitting comming out of the fuel supply pump with the 22mm connector removed. You will see that due to the fact that that fitting helps hold and guide the supply pump outlet valve there is a restriction down there. I think putting a bigger hose will not help due to the restricion down inside of the supply pump itself.

If you just have to have a 3/8 hose barb down their- drill out a 3/8 hose barb to fit over the metal part of the origional barb and glue it to that barb with JB weld or another good quality epoxy. But do it so that the 22mm nut will still rotate.
Please comment back to me.

deezulmark · #4 07-11-2008, 01:16 PM

Thanks for the replies. Sounds like it's a custom fitting that would be hard to find.

I guess I will just install a double-ended barb at the filter end of the the hose to adapt to 3/8". I'm installing the Elsbett VO kit and they route the output of the primer to their heat exchanger before going back to the filter. The input to the heat exchanger is 3/8". They also install a 5/16" line from the fuel tank to help the more viscous VO to flow better until it gets to the heat exchanger. So I figured I should try to keep the diameter larger until I got to the heat exchanger.

Maybe I shouldn't worry about that small restriction in the warmth of the engine compartment. Or maybe I should put the heat exchanger before the primer pump... The input to the pump seems to be 5/16, as is the output of the heat exchanger.

Mark

Diesel911 · #5 07-11-2008, 05:01 PM

Yes, 5/16 hose fits fine on the inlet side of the fuel supply pump.
Besides the restriction inside of the supply pump outlet the return line that comes out from the valve on the Fuel Injection Pump also has aprox. 1/4 inch I.D. hose. I also replaced that one with 1/4 rubber hose. So it is restricted on both ends at the supply pump and at the valve end to 1/4 inch.