Tomcat combining fuel tanks

joechiro30 · Posted: Wed Apr 18, 2018 12:13 am Post subject: Tomcat combining fuel tanks

I have a Tomcat 2006 and we want to be able to convert our fuel lines so that we can utilize either gas tanks. Currently each engine has its own gas tanks but I would like to be able to siphon the fuel lines so that one engine could utilize both gas tanks. The purpose for doing this is to be able to use both gas tanks if one engine fails the other engine can use both gas tanks. Also to be able to balance the boat by utilizing one gas tank. I put more fuel in the port gas tank because the over all weight is heavier on the starboard side with the water tank and sewage all on the starboard side.
Has anyone made these changes to your boat and have any tips or advice to do this project.
Thanks

thataway · Posted: Wed Apr 18, 2018 9:27 am Post subject:

Basically takes a "T" off each tank, a few feet of hose and a two way valve--such as in the C Dory 22's, to select tank "P" or "S". The connections can be made up at the fuel filter, so that the only extra tubing is under the transom or aft seat.

If you want to pump gas from one tank to the other, then a two way valve on the intake and output of a Walbro ignition protected fuel pump.

It can be very complicated or very simple. I would go with the first choice.

rogerbum · Posted: Thu Apr 19, 2018 10:25 pm Post subject: Re: Tomcat combining fuel tanks

joechiro30 · Posted: Fri Apr 20, 2018 1:20 am Post subject:

Thanks for the diagram roger. What do you need the valves for each tank?

joechiro30 · Posted: Fri Apr 20, 2018 1:21 am Post subject:

Also I believe that our 2006 tomcat has the 130 gallon tank
Is
That correct?

Dreamer · Posted: Fri Apr 20, 2018 11:02 am Post subject:

Joe, Our 2006 TC-255 had two 75 gallon tanks.

rogerbum · Posted: Fri Apr 20, 2018 11:39 am Post subject:

pwsuser · Posted: Sat Apr 21, 2018 11:01 am Post subject: Tomcat combining fuel tanks

Hi, I have a 2006 Tomcat and I combined my tanks the way it showed in the diagram. I did a quick job and my combining valve was not always easy to find so I redid it. This time I used just two T valves and mounted them on the fuel filters so I could reach them. With just two valves when you run normally from one tank to one motor the gas runs across the top of the T valve and the bottom valve is closed. To run say both motors from the starboard tank then the starboard T valve will have gas coming from the tank into the top left portion of the T valve and running to the motor out the top right portion of the T valve, like when you run with one motor on each tank, but now the bottom portion of the T valve must also be open and this crosses over to run the port motor. So all three holes in the T valve need to be open. The issue is that I could not find a T valve with three holes, so I bought 2 with two holes, took them apart and drilled a third hole. Now it works fine and I only have two valves to find and switch. Hope this wasn't too confusing.

Dave

Robert H. Wilkinson · Posted: Sun Apr 22, 2018 10:05 am Post subject:

With an electric fuel pump - no problem, but for anybody with mechanical fuel pumps it can be problematic if you run one tank dry. My Campion had twin tanks with a switch and a mechanical pump. If I ran 1 tank out it required a LOT of cranking to get the mechanical pump primed from the second tank. Excessive cranking can lead to a number of problems. I eventually installed an electric pump in line solely for the purpose of priming. In the event of a mechanical pump failure I could have re-plumbed the electric to by pass the mechanical pump. Gas should not be pumped through a defective mechanical pump. If the diaphragm is compromised you can end up pumping gas into the engine crankcase(diluting oil).

Regards, Rob

PS. This experience pertains to an older inboard. Smaller outboards may not have this problem esp. if it includes a priming bulb in line.

PSS. All switches need to be clearly marked and easily accessed. You always need to be 100% sure where you are drawing gas from at any given time. Sometimes in rough weather you may run your tank empty quicker than expected and need to get re started as quick as possible. Rough weather and a low tank can also stir up crud and suck it into your filters.