THE PORTAL HUB - Pinzgauers, Haflingers, Volvo 303s and more!

Has happened twice in last month. When I get to 1/2 tank indicated the truck stalls out. Otherwise the truck is running fine. If I add gas to the fuel tank at this point it still will not start until I prime the fuel line on the gas tank side of the fuel filter with a separate gas can and hose.

Is there a submerged fuel pump in the gas tank in addition to the mechanical pump on the engine?

Thanks,
Sam ('71 710K)

P.S. The gas gauge is working fine i.e. 1/2 indicated is 1/2 actual.

BTW, I rebuilt the fuel pump on the engine about 3 years ago with a new kit.

Look for cracked supply hose or loose hose fit on suction side. Also you can pull the fuel sender out and look directly at the pick up for debris.
I used a different gas can the other day and now I have a oil cap or additive cap gasket in my tank , it has gotten sucked to the pickup twice now Guess I'll have to get it out before the next road trip on Sunday.

If the truck had sat for an extended period of time, your pick up tube might have rusted and developed a pin hole at roughly half a tank. This would mean that the truck sat with half a tank of fuel. This is a minorly common issue with Unimogs.

Is the supply hose rubber? And is this the hose going from the fuel filter to the gas tank? How do I access the fuel sender?

Sorry for all the questions. I appreciate your time.

Fuel line is rubber until it attaches to the feed pipe at the tank.
Pull the seats and engine cover to check all the lines. Also check any hoses and connections to gas fired(BN4)heaters.
Pulling the sender is easy. The access panel is in front of the right forward rear seat. Remove the 4 screws and the plate. You are now looking at the top of the sender, tie a string or secure the sender wire with a pair of hemostats(locking type), now remove the wire, pull the 5 screws from the sender and lift it out slowly so it drains into the tank, not on it. Now you can see all the way to the fuel pick up

Jim,

That reminds me...thank you for giving me the fuel can spout. The fuel gauge is not accurate on the 712. I ran out of gas in the middle of nowhere. I was able to pour in the extra five liters from the jerry can, which got me to town no problem.

Between the two pinzies, I have a very long shopping list going! First is a good set of tires for the 712, then I can at least pass inspection.

-Evan

I would suspect a hole or problem at the fuel pick up line ~ pull the systen as stated by others, fix and carry on!

Its a series of tubes... like the internet.

Thanks Jim for the detailed instructions and to the others for your suggestions. I leafed thru my repair manual and was not able to find a section addressing this . I'll let you know what I find.

Thanks Jim for the detailed instructions and to the others for your suggestions. I leafed thru my repair manual and was not able to find a section addressing this . I'll let you know what I find.

Jim, I have a 710K and can't seem to find the 4-screw access panel you refer to. Is the access panel accessed from the rear seating area or the front. I removed the small dog house over the gasoline fill tube are but do not see the sending unit.

Thanks,

Duh! Found the access panel. I'm going in!!!

Jim,

The sender is out and yes I can see what i think is my pick up tube (slanting from the top front of the tank to the bottom back of the tank) but I can not reach it or work on it thru that small access hole (sending unit hole). Do I need to drop my tank to gain access to the pick up tube to analyze (repair) it?

Thanks

Ok, here is the way to check the tube without removing it: Pull the drain plug and the tank end is exposed. Plug it with a finger tip and either use a vacuum pump on the other end or low air pressure, or your mouth to charge pressure or suck and see if it leaks down. If it does not leak, replace the fuel lines to the pump(filter included) and block off the heater fuel supply hose. Also check for gas smell in the oil (bad pump diaphram).
That should get you there!