“Our Hunter 34 has a 25-gallon fuel tank. We’d like to add a 20-gallon tank so we won’t have to carry jerry cans on deck. I estimate the two tanks will be about a foot apart. What is the best way to hook up the second tank so air can’t get in the fuel line? I’d like to avoid having to pump fuel from the new tank into the old one when it gets low. Unfortunately, there isn’t enough room to install one larger tank. “
— Bill Siegworth , Beloit, Wisconsin
Don Casey replies : All you have to do is tee a supply line from the new tank into the existing line running from the old tank. You’ll need to install fuel shut-off valves between the tee and both tanks so you can use fuel from one tank without draining or filling the other. If the old tank has a shut-off valve, locate the new tee fitting downstream of it. When you want to change from the old tank to the new one, just open the new tank’s shut-off valve and close the valve on the old tank. To switch back, close the new valve and open the old one.
You could combine the tee and valves in a two-tank valve with two inlets and one outlet, but I think it’s better to have separate valves for each tank. Whatever arrangement you choose, plumbing the new tank will require breaking open the fuel-supply line, which will introduce air into the system. That means you’ll probably have to bleed the engine to make sure it will start. But once the new tank is filled, and as long as the fuel level doesn’t drop below the bottom of the pick-up tube, you shouldn’t have any problems with unwanted air getting into the system.