Running starboard engine off port fuel/water sep?

[duped]

Hi, I have an idea that I was trying to gain some professional opinion on before attempting. I have a boat with twin 5.7l carbureted Mercruisers. My power steering is on starboard engine only, leaving me forced to troll only on that engine to keep my hydraulic steering system happy. (Unfortunately seastar specs I must use PS with this ram.)

I have hit dead ends on fitting a second PS pump to the port engine, the logistics of that is beyond my capabilities.

I have two side mounted 75 gallon tanks which each feed their respective engine ONLY. I understand there are fuel selector valves available that this boat unfortunately didn't come with, but we're talking a lot of plumbing there. Truly, all I really want is to run the STB engine off the port tank. I DONT need run the port off of STB or run both off one. When trolling, I run the port tank lower and have to refill it twice as often, and it would be great to balance the tanks.

Anyway, I know the factory fuel/water separators have two inlets and two outlets per engine. Is there anything wrong with my wacky idea of installing another fitting into the 2nd outlet of the port engine's filter housing to feed the STB engine? I'm thinking install a quality shut off valve right after the new fitting that I will turn off whenever the port engine is running (so I'm not running both engines on one 3/8" line), and then install another shut off at the line coming into the STB filter from the STB tank and be done? Anyone ever try this, or should I just suck it up, buy the selector and re-plumb everything?

 

[NHGuy]

Yes you can do that but you'd better plumb it right and use sealer, (not tape) on the fittings. If you forget and run both engines off the one feed you could get a lean condition at higher loads... Which if allowed to continue can break stuff in the engines. So you'd be better with a set of fuel selectors.

 

[duped]

Thanks for the input, I'm always hesitant to mess with anything fuel related and will ensure whatever I do is done safely. I just figured doing what I suggested would result in a few less fuel lines running around. With the selectors I'd need two valves to do it correctly, for a total of 6 lines. This keeps it to a minimum.

The other thought that has come to me is just running two lines between the two separators and have them pull fuel from any tank at any time. Not sure if they would naturally balance out this way, or if I'd have airlock or fuel starvation problems?

I'm not familiar on how other vessels with twin gas engines balance the tanks if they don't have selector valves. I know with diesels you're permitted to have a balance hose at the bottom of the tanks, but that isn't legal, let alone possible for my boat.

 

[achris]

Merc used to do a thing called a 'Priority Valve Kit' to run a single steering system with 2 engine each with a PS pump. Unfortunately hasn't been made for years... That doesn't help you, but this may. As well as the problem of only one engine with the pump so when you're trolling you can only run the starboard engine, if you have a starboard engine breakdown, you have no steering. Not a good look. Why not set up a PS pump on the port engine and run it though a manual 'changeover' valve? Very very simple thing to do. All you need is to put the pump on the port engine, and fit a 2 way crossover porting system. Remember that as these pumps are constant displacement you can't just close off the hoses, they need 'return to tank' valving.

The valving would work like this... When in 'Position 1' the 2 hoses (pressure and return) from the stbd pump would be routed to the ram and the hoses from port pump would be joined together (gets over the problem of constant displacement pumps). When in 'position 2' the hoses would be reversed, port pump hoses to the ram, stbd hoses to each other. You could make it a simple hand/manual changeover, or electric. Gets around the problem of uneven fuel burn, and allows for the engines to 'clock' similar hours. Also gives you an engine to come home on should one fail.

One last thing. You can't just 'common' the return lines. One pump would be overfilled, the other starved. You need to isolate and switch both hoses.

Any decent hydraulics shop should be able to help you with a valve body and electric solenoid.

Chris......