hey folks,
how exactly does the dual tank setup work? Im assuming there's an output on both tanks that go to a switching valve? My friend who I bought the truck off of says the valve or switch doesn't work. Not sure which, but I don't know how to check it. I don't want to switch tanks either yet because I don't know whats in the front tank and if its still good. I fear running old fuel (that only god knows how long its been sitting there) through my engine.

On a side note, if I drain the front tank, fill it then get the switch or valve (whichever) to work, I need to prime the lines. I've heard of people doing this with a small electric fuel pump. Where can I get one cheap and is this a good idea?

Thanks AGAIN!
-Al Conforti

 

Al,

The tank selector valve is mounted inside the drivers side Frame somewhere around the drivers door. The selector switch should be to the left of your steering wheel.

Since the Diesels have return lines from the engine back to the tanks you should have two lines per tank running to the selector valve and then two lines (feed and return) running to the engine. There should be an electrical connector to the selector valve. With all the hoses and the electrical connections it probably is not the easiest thing to change. I know on my 91 the valve is actually located closer to the box and is hard to get to because it is sandwiched between the front tank and the frame. On the 93' the selector valve has easy access as it is located in the vicinity of the drivers side door.

Pulling the front tank is not a big deal if you don't mind struggling with a few rusted bolt that secure the tank guard and tank starps.

Check you tanks for rust. The rear tank on my 91 had rusted out because of mud that had collected between the tank and guard. I was able to save the front tank by coating it with some good rust paint.
If your diesel in your dead tank is more than a year or two old I would dispose of it, flush it with some new diesel and then fill with new.

Priming the lines is a good idea but usually not very practical. I would fire up the truck on the fuel in the filter and bleed air from the schraeder valve on the filter as it runs. If you don't catch all the air before it gets to the IP the truck might stall and then you are into a normal bleed procedure. Just don't crank your starter for too long to avoid burning it out.

If you got the money to spend. On my 91 I added an electric pump on a push button between the existing fuel pump and Fuel Filter. I just push the button whenever I change a filter until I get out all the air thru the Schraeder valve, sure saves my starter. On my 93 I got a manual fuel pump that came with the Racor Filter I installed; again this allows me to air free the entire fuel system before I start cranking.

Air freeing the lines helps.

 

You can buy a new valve at a parts house. I don't remember how much it cost. But they have a plug for wires and all you do is switch the fuel lines and unplug the old valve and plug in the knew one.

 

On an 85 the tank switch is on the right side of the heater control panel.

With the engine off and the key on, you can hear the valve switch. Check the electrical contacts on the valve if it does not switch.

 

Don’t forget to check your fuses, my father ran his van for 3 years on one tank. I went and bought a new valve to install for him and it still didn't work so I started checking wiring only to find a blown fuse. Put the old valve back in and it is still working.

 

The default tank is the front tank on my 91. I don't know if all models and years used the same valve but if the power is cut off to the selector switch or to the valve the valve opens to the front tank. It's possible that a shorted wire could keep the valve energized regardless of which position the switch was in. If the fuse isn't blown you might try disconnecting the wires from the switch and see if the valve switches to the front tank. Also, with the wires from the switch disconnected it should be easy to check the switch.