Priming Pumps and (not vs.) Cross Connects

[racclarkson@gmail.com]

There has been a good deal of posting on the value of having a fuel priming pump onboard for filter changes. It's a good idea. In a posting, I suggested an alternative that I use which is cross connecting the motors (1271's) from secondary filter to secondary filter with a fuel line installed overhead and a ball valve. This is why that's a good idea.

I was headed for week's cruise from SC to FL last week (1983 55C). Knowing I wanted fresh fuel in my reserve (forward) tank and having room in main (aft) tank, I selected the supply from the fwd and return to aft. Being a senior citizen, I ran the fwd tank dry starving both engines--a stupid math error. The port motor died on me. I was able to cut the starboard motor just before it stalled. I dropped my hook which held perfectly and commenced to studying the situation. I spun off my port secondary and it had very little fuel left in it. I filled a replacement unit from my priming fuel can and proceeded to learn that Murphy was with me. My replacement secondary's were of the wrong thread pattern--turns out it wouldn't have mattered. Put the old filter back on.

I switched both motors to the aft tank, but the port refused to make any power and stalled repeatedly. The starboard motor sputtered and regained prime then power. No such luck with the port side. With the starboard running normally, I opened the cross connect valve and the port motor cranked and regained normal ops after a bit of sputtering. Gotta love those low-tech Detroits.

So, I planned to cautiosly limp along to my planned first night's stay and pick-up some good replacements. Well, I ran the rest of the day working up to full cruise with the port feeding off the starboard motor--fuel pressure at 1750 rpm was north of 40 psi which is my norm. No filters were to be found at my first stop (Sat. afternoon). Thus, I changed plans to run ICW from Pt. Royal to Brunswick instead of outside because of no spare secondary's. Again, ran entire day cross connected as per normal. I did drain and replace Racors before getting underway which were somewhat gunked up.

Found several spares in Brunswick, and also found line clogged before primary and secondary filters. Disassembled and blew lines clear plus used shop vac and air to pull trash out of fwd tank pick-up and close cross connect valve. Decided to not replace secondary and run and see--a short run by sea to Fernadina. Vac gauges showed no indication of further restriction--a good day. Nevertheless, I changed secondary's. No need to make a mess and pre-fill. Just spin it on, start opposite motor and open cross connect valve for 30 seconds. Reversed process and it's all history but with a happy ending. Plus, found out fwd tank is pretty clean (bone dry) and now has 100% new fuel.

So, a priming pump is a good idea as it has been said. A cross connect is also a good idea that allowed me to continue my trip. Had I lost power in the ocean, as opposed to a sound, the good idea would have instantly become a great idea.

Moral of the story: Don't draw and return to different tanks. Install a cross connection in case senior citizenry cancels the first rule. Besides, I would have probably forgotten where I stowed the priming pump anyway. Robert

[saltshaker]

This is why I like to burn down the reserve tank when I'm getting ready to fuel up. Don't blame it on age. I did that once and was in my early 30's. Now if I want to transfer fuel I'll do it in the slip or set a timer with a very conservative estimate of when to switch back to normal.

[dar636]

Hi, have you a diagram of the cross connect plumbing? I've currently only single racors for each engine and am planning to install dual filters this winter with pressure gauges. Adding a cross connect at the same time would be easy.

Thanks-

[Cricket]

This is what we have for fuel priming, 2 engines and 3 tanks. Turn supply fuel valve to off of engine that needs Racor filled/primed and also the return valve of other engine (running) to off position, this will fill the filter. The valves are 5 port. We also put in a polishing system with a manifold to be able to pick up and return fuel to any of the tanks with an outlet in the ER just in case the jug etc needs to be filled. Added pickups and returns to each tank for the polishing set up, has come in pretty handy a few times.

[racclarkson@gmail.com]

To dar636,

I can take a pic in a couple of days when I get back to boat. My spin on secondary filters housings have a extra outlets that are normally plugged. We just removed the plugged outlets and put in male pipe fittings (both ends) and had two hoses made up. Both hoses go from filter housings and meet at a convenient spot and connect to the valve. Another plug was removed to accommodate fuel pressure gauge. Pretty straight forward stuff. Remember to never use teflon tape with fuel connections.

[racclarkson@gmail.com]

As promised, here are a couple of pics. As you can see, this is a pretty straightforward modification.

IMG_6975.jpgIMG_6976.JPG

[jim rosenthal]

So, if I understand this right, you use the fuel return from the running engine to prime the engine that has lost prime?

I think most priming pump installations are permanent; some fuel filter systems also come with a hand priming bulb installed on them. (Seaboard Marine) which work surprisingly well. I have one on my home generator set which is a NL843, I think it is. 16kW.

[rsmith]

Not a bad idea. The secondary is after the fuel pump so your running both engines off the one pump. Most people don't understand the fuel system. When you lose fuel pressure due to an empty tank or not shutting off the supply while doing a filter change the system gets air bound. Since the secondary is on the pressure side of the engine fuel pump you need to loosen the secondary while cranking the engine to purge the air. Just filling the filter won't clear the lines. This is why I don't like the spin on filters. I've ran my tanks dry many times on long runs to make sure I've used all the fuel available. 90% of the time you can just pull the throttles back when it sputters and change tanks with no problem. I NEVER EVER RUN BOTH ENGINES OFF THE SAME TANK!!!
That said if you look at the tank pickups usually one engine feed is at the forward end of the tank the other is at the aft. If you use the engine that utilizes the forward pickup when the boat comes off the plane the fuel rushes forward and keeps the engine running.

[tonytrakovich]

So, if I understand this right, you use the fuel return from the running engine to prime the engine that has lost prime?

I think most priming pump installations are permanent; some fuel filter systems also come with a hand priming bulb installed on them. (Seaboard Marine) which work surprisingly well. I have one on my home generator set which is a NL843, I think it is. 16kW.

Looks to me like he is using the Pressure side of the fuel supply line on the first engine to pressurize the and prime the secondary on the second engine. This is after the fuel pump on the second engine. Does this mean the fuel pump on the second engine is running dry for some amount of time? Is that good for it?

[racclarkson@gmail.com]

This is not return fuel. The fuel comes from other engine's secondary (before it is sent to injectors). This works at speed because of the large volume of fuel Detroits pump. Set up as it is, the fuel in the disabled engine flows both ways from it's secondary under 40 psi and lubricates it's fuel pump on one side and feeds injectors the other way. 12 hours of crossover ops prove the point.