Saddle Tanks Overflowing After Fueling

[ahoke]

Hi all,

Picked up a '72 C20 Custom Camper this summer with the two additional travel tanks added on either side of the bed. When I purchased the truck, the owner said he didn't use the cab tank because it smelled like gas when he did.
Essentially once I fill up, I'll drive it and park it and some time later one saddle tank or the other will overflow, leaving a slight puddle of gas on the ground. When parking I'll look underneath and there will be no sign of leaking but then coming out of the grocery store, for example, there will be the leak 20 mins later. Anyone have any similar issue? Curious if I just need to replace the 4 way brass tank selector valve or if it's more than that. Also I never fill the cab tank since the previous owner mentioned the fume issue. Initially I thought maybe the valve was bad and the fuel left in the cab tank was slipping back into the saddle tanks due to gravity and maybe it takes that long for the fuel to accumulate into the tank that I'm using.

If y'all suggest trying a new valve any suggestions on where to buy one? Seems like a marine part. I imagine it'll need to be 3/8 inch since it's a 350 sbc?

[Sheepdip]

Expansion

[Stocker]

My K20 also has twin saddle tanks. I have never experienced the problem you describe. Maybe your tanks are just being overfilled, and like Sheepdip said, expansion.
Maybe you can get lucky and catch it dripping, then you'd know where it's coming from.

If it is a bad valve, those are available. RV supply places should have them, and a Google search will definitely find them.

[Sheepdip]

That cab tank smell is very fixable. No telling how long any residual fuel has been in there but by removing the tank and cleaning it, replacing any evap/fuel line hoses a new sender/pickup tube and gasket you should be good as new.

[kwmech]

You didn't mention where the tanks are leaking. AND I would check into where or why the cab tank smells.

[PbFut]

In 1972 return lines were used in the fuel system. This circulated the unused pumped fuel back to the tanks to reduce vapor lock. Auxiliary tanks may or may not have been properly plumbed to receive the return fuel. The valve needs to be stacked so that the selector switches one circuit of supply and one circuit of return fuel in sync and directing to the correct tank. Often the return was not switched on aftermarket tanks and the return fuel simply went back to the main tank. So the owner had to always run the main tank low, then switch to Aux. Then back to main to finish using the returned fuel. It is possible the PO changed the return line to enter one of the aux tanks and you are over filling when using a different tank. Or the return lines got mixed up during a repair. Given you describe overfill after driving for a period of time, the above seems to line up.

[Dead Parrot]

Check for an "always on" connection between the tanks. Either a direct hose connection or a bad/leaky valve. Fuel can flow from the uphill side to the lower tank. If both are full, it doesn't take much fuel to overflow the lower one.

[GASoline71]

Could be as simple as an old cracked rubber fuel line. Check them all.

1971-72 also has an "EEC system" (Evaporative Emissions Control) that vented the tank through a series of tubes and though a charcoal canister, instead of venting out of the gas cap like 1970 and earlier. Not sure if that system would affect the extra tanks in the bed, but if faulty/clogged/rotten could be contributing to the "gas smell" in the cab.

Gary

Gary

[Fbks_Cruiser]

Not sure about C20, but my 72 K2500 (also 3/4 ton) never had any eec and the tank is vented through the cap. No return line. I'm pretty sure those pollution control measures got installed on the 3/4 ton later than the 1/2 ton trucks. So, given that, I would think overfill, or faulty selector valve that is letting fuel pass from one tank to the other. I would replace all of the rubber lines with new ethanol resistant ones and test the selector valve. As for the in-cab fuel smell, if your system is non-eec like mine, there is not much to check besides the sending unit and gasket. My tank did have a leak right where the filler neck joins the tank. As a temporary fix, I smeared JB Weld all around that joint and the bit of fuel smell I had when the tank was full is now gone. I don't feel too worried about the JB Weld patch as the tank is not under pressure and there is no stress at the joint. My "temporary" patch is going on 3 years now.

[PbFut]

Tank venting and return fuel is different. 72 C20, C30 and above did not have tank vents, even in Calif. They had cap vents but all had return fuel ports. Both saddles are at same level and main tank's bottom is higher than the two aux, but is not used as per OP. Possible fuel from return is only flowing only back to main (common for aftermarket setups) Then down to the aux tanks. If the hoses have been messed with by PO who did not understand the correct paths or it's an aftermarket set up that did not switch the returns. I am assuming OP has identified the leak is coming from a overfill situation and running out the cap.
As far as valves. You can by electric actuated valves that will switch both supply and return as well as send correct sender unit info to the gauge. The electric valve will only switch between 2 tanks. If you want to switch 3 tanks, you will need two units. I have mine set up with two valves to control 3 tanks. The fuel gauge is always in sync with the correct tank and the return line and supply lines also always in sync. No guessing or checking to see I have the gauge switch and floor valve selector correctly sync'd and no overfill issues. The electric valves are about the same price the brass manual valves but it takes a bit of electrical knowledge to find the correct rotary switch and wire it correctly. When you are done, you have a factory look and feel of the electric gauge selector on the dash and no floor valve and a correctly working fuel select system..

[57taskforce]

Originally Posted by Fbks_Cruiser

Not sure about C20, but my 72 K2500 (also 3/4 ton) never had any eec and the tank is vented through the cap. No return line. I'm pretty sure those pollution control measures got installed on the 3/4 ton later than the 1/2 ton trucks. So, given that, I would think overfill, or faulty selector valve that is letting fuel pass from one tank to the other. I would replace all of the rubber lines with new ethanol resistant ones and test the selector valve. As for the in-cab fuel smell, if your system is non-eec like mine, there is not much to check besides the sending unit and gasket. My tank did have a leak right where the filler neck joins the tank. As a temporary fix, I smeared JB Weld all around that joint and the bit of fuel smell I had when the tank was full is now gone. I don't feel too worried about the JB Weld patch as the tank is not under pressure and there is no stress at the joint. My "temporary" patch is going on 3 years now.

This EEC is a 1/2 ton thing for the most part in 72. Higher GVW trucks weren’t required to have the charcoal canister and the other stuff that goes with it.

[BROWN 70]

I have a 70 GMC and it has Colorado leisure products saddle tanks. haven't had over flow problems but I don't fill them all the way up. good luck, BROWN 70

[Getter-Done]

All great suggestions above.

I have also seen the tanks have a hole rubbed in them on the top at the bed rails.

The bed rails rub a hole in the tanks after all these years.

They would have to be full to the top to leak there,
Or be park on a slope.

[71CHEVYSHORTBED402]

Originally Posted by ahoke

Hi all,

Picked up a '72 C20 Custom Camper this summer with the two additional travel tanks added on either side of the bed. When I purchased the truck, the owner said he didn't use the cab tank because it smelled like gas when he did.
Essentially once I fill up, I'll drive it and park it and some time later one saddle tank or the other will overflow, leaving a slight puddle of gas on the ground. When parking I'll look underneath and there will be no sign of leaking but then coming out of the grocery store, for example, there will be the leak 20 mins later. Anyone have any similar issue? Curious if I just need to replace the 4 way brass tank selector valve or if it's more than that. Also I never fill the cab tank since the previous owner mentioned the fume issue. Initially I thought maybe the valve was bad and the fuel left in the cab tank was slipping back into the saddle tanks due to gravity and maybe it takes that long for the fuel to accumulate into the tank that I'm using.

If y'all suggest trying a new valve any suggestions on where to buy one? Seems like a marine part. I imagine it'll need to be 3/8 inch since it's a 350 sbc?

I don't believe your valve is the problem, serves as a selector, that's it, though been wrong before, often That is unless it's seal(s) are no good, hmm. Doesn't seem likely.

Beyond expansion, don't fill em up then. That said, your tanks would be well rusted by now without care, IMO. Could need new hoses instead, due a replacement by now for sure.

The reason the interior tank stinks is most likely bad hose(s), which may include to the canister, the canister itself, the sender and/or sender seal; perhaps unlikely a fuel/vapor separator. That stuff is easy to fix with the seat out. If never done before it's due. You can pull the tank as well, check for rust and clean. Do that problem solved.

[Steeveedee]

As for stench, I've had locking gas caps, and when the seal goes bad after not many years, they leak. Did away with a locking cap, and all is good. The non-locking caps have a different type of gasket and don't leak as much.