Fuel injection fuel line return fitting options

Looking for some opinions/guidance. I think I have it sorted out but I just wanted to run it by the experts real quick.

I have a 1985 Baja Sunsport 190 with a built 305. I've only had the boat a few months so most of my boating time has been spent fixing shoddy workmanship and lack of maintenance.

The previous owner has fitted the boat with Mallory Marine fuel injection. It runs and runs good but there are a lot of issues that need addressed for safety etc.

In order to run the fuel injection return line to the tank he has fabricated some kind of T-fitting that he spliced into the fuel tank vent line. It works but I know it's not correct and more importantly it has a tendancy to leak a slight bit of fuel during use. Big time no-go. I've attached some pictures of the wonderful work just as a reference.

Just so happens my fuel gauge sending unit is leaking and needs replaced as well. While searching the internet I found a sending unit that also includes a return line fitting. I'm pretty much set on buying this unit but I wanted to make sure there weren't any other options out there before I bought this one.

Here's what I'm looking at (disclaimer , I did not see this for sale on iboats or I would be linking to it)
http://www.amazon.com/Moeller-Marine-Electric-Sending-Diesel/dp/B000MTI15U

Re: Fuel injection fuel line return fitting options

Man that's ugly... in more ways than 1.

Remove the fitting in pic 1 that the fuel line hose barb is attached to. (prolly best to remove the barb first. Then instal a brass female T fitting that's at least 3/8ths. Put your original barb on 1 end, a new 3/8ths fuel line barb on the other end, and you'll be good to go. Make sure you don't use teflon tape on the fittings and double clamp all the fuel lines.

Re: Fuel injection fuel line return fitting options

I had to go through something similar when I converted my boat to EFI.

The only proper way to do it is plumb a return line into the tank.

Here's what you should do.

#1. Drain the tank. You can use you're fuel pump to do it, if you're careful. (don't be a dumb-***, no sparks, and have a fire extinguisher on hand)


#2. Un-modify you're vent. What he's got going on there is going to create a LOT of fumes and hydrocarbon emission out you're vent. It will likely make the boat stink like gas fumes, as well as create a fire hazard.


#3. drill and tap the top of you're tank with an NPT fitting.

#4. Use a 90 degree NPT barb fitting for the return. DO NOT USE TEFLON TAPE. the company that makes loctite makes a great thread selant that works well with fuel.


then you're going to have to come up with a way of cleaning all the metal filings out of the tank from drilling it.

The other option is to go with a returnless EFI system, but this requires more specific parts (pump, fuel pressure regulator)

also remember, EFI uses specific hose clamps. they have fine threaded machine screws, and look nothing like you're classic coolant "hose clamp"

the clamps shown in those pictures have no business being part of an EFI system, even on the return side that is considered to be low pressure.


For my EFI system, I had my local hydrolic hose shop fab up hoses with crimped fittings. Rated for 3000 PSI in situations with a lot of movement. The hoses were very inexpensive, and the end result is no worrying about any clamps. just NPT fittings and thread sealant all around.

Re: Fuel injection fuel line return fitting options

Yet another reason to buy a boat with a fuel injected Mercruiser or Volvo Penta engine. No return line to the fuel tank. They recirculate on the motor. Very slick.
Sorry you have a cobbled up system. I hope it works out for you. if you can't get it to work right, I'd suggest you try to copy what Mercruiser or VP uses, cause it works perfectly every day. And it's Coast Guard legal.

Re: Fuel injection fuel line return fitting options

Thanks for all the good suggestions and info.

Here are some of my thoughts...
I'm not looking to T into the vent line at all, I want to completely do away with that scenario.

Drilling and tapping the tank is an option..but it's an option I'd rather not explore if I can help it.

I think short of replicating the Merc/Volvo no return line setup I think I'm heading down the right road using the sending unit with the built in return line fitting... ??? Yes/no/maybe?

Speaking of the stock merc/volvo setup, does anyone have a picture handy of how that's configured?
And yeah I know.. that looks like (and is) a cobbled up mess. Surprisingly it runs well, very well actually. I'm all about doing things the correct and safe way so I just want to get this sorted out and move on to the next back yard engineered problem I need to fix

Re: Fuel injection fuel line return fitting options

I suspect a returnless system may not be possible in you're case.

You're fuel rail, fuel pump and fuel pressure regulator all have to be designed to work with a returnless system.

Most automotive systems ran a return until 2003-2005 ish... then went returnless.



And while you MAY be able to modify the system to work without the return, you're long term reliability may be compromised.

You're fuel pump is likely designed to have continuous flow through it, if you go returnless, it will be pushing up against the regulator, and the only FLOW through it will be what the motor actually uses.

You're fuel rail is most likely not that complicated of a design, and most likely does not take into consideration temperature and air bubble issues.

A fuel rail is naturally cooled by the fuel circulating through it. If you go returnless, you loose that cooling effect, and run the risk of vaporlock.


So my advise is, unless you're system was deigned from the ground out to be returnless, don't try to modify it. there is a REASON auto makes used the return for 25+ years.

Re: Fuel injection fuel line return fitting options

Couple of problems here that I see.

#1. Drain the tank. You can use you're fuel pump to do it, if you're careful. (don't be a dumb-***, no sparks, and have a fire extinguisher on hand)

Click to expand...

Not necessary. An empty tank is all fumes and will blow up faster than a full or 3/4 full tank. Yes, be careful and no sparks.

#3. drill and tap the top of you're tank with an NPT fitting.

Click to expand...

Don't even think about that. First of all, most tanks are only 1/8" thick aluminum at most. Not enough to tap with pipe thread.

Don't do anything yet, I will explain how I have safely made return lines for diesel using safe methods. Just give me s bit to put it together.
I really don't think trying to copy what Merc and Volvo did is a good idea without really knowing how your system really works, and as far as I know, there isn't anyone on this forum that uses that EFI system.

Re: Fuel injection fuel line return fitting options

My tank IS 1/8 alum, and was drilled and tapped from the factory for the pickup.

I drilled and tapped mine for the return.

Re: Fuel injection fuel line return fitting options

No no... I'm not talking about putting a T in the vent line. The vent line should go back to nothing more than a hose that connects to a through hull tank vent fitting.

I'm talking about putting a T inplace of the existing 90 degree tank fitting that you have. Have a look at this...

http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053

You need to get one that's 3/8ths ID, and the appropriate fittings match up to the tanks thread if it doesn't fit directly. The important thing is that any/all fittings must be at least 3/8ths ID, and the fuel line barbs must be 3/8ths ID. You can't go any smaller.
The fuel return line will just dump into the existing fuel supply at the tank fitting.

Re: Fuel injection fuel line return fitting options

Ok, here we go.
1st, get a fuel sender gasket or 2. You WILL need one at least.

Get a piece of 3/8" or even 1/2" thick aluminum at least a 1/4" wider than the gaskets outside diameter, and long enough to clamp to something (6" or 8" ) later on.
Now, get a holesaw that has the inside of the holesaw the same size as the gasket. (or at least real close. a little oversized is better than undersized.
Using the hole saw, drill about 1/2 to 2/3 of the way through the aluminum (all the way through with the pilot bit.
Now, use the gasket as a template and drill some pilot holes for the mounting screws around the OD of the aluminum disc. Then drill out the center hole and tap for a 1/4 NPT fitting.
Next, finish drilling with the hole saw so yu have the almost completed disc.
Put the aluminum disc on the tank where you want the return to be. Stay as far from the pickup as possible to prevent bubbles from being a problem.
Drill the pilot holes from the disc to the tank. I use a few of the same sized drill bits. Drill one hole, stick a drill bit through the disc and into the tank. Drill another on the opposite side use another drill bit to stick in that hole. Now drill the rest of the holes.
Now it's time for the accurate part. Drill those small pilot holes in the disk to the same size as the OD of an 8-32 tap (USE A DRILL PRESS AND MAKE THEM STRAIGHT)

Drill the tap drill size in the holes in the tank. Use the disc to keep your tap straing up and down and tap the 8/32 threads in the tank.
Use a 1/32" larger bit in your drill press and enlarge the hols around the outside of the disc.
Back to the tank, drill a 5/16 to 3/8" hole in center of the hole circle so the fuel can get to the tank.
Install your fitting, with gasket, and use some sealer on the threads of the screws and tighten down the disc to the tank. Do not overtighten, or you will rip the threads out of the screw holes.

To keep shavings from getting into the tank, use some grease on the end of the drill bit. Take your time and clean it often and put on new grease.

The gaskets and the method works for gas fuel tank senders, will work for home made return lines as well.

Haven't typed this much in a long time, hand hurts. Hope this makes sense. If not ask.

Re: Fuel injection fuel line return fitting options

JustJason said:

I'm talking about putting a T inplace of the existing 90 degree tank fitting that you have. Have a look at this...

Click to expand...

To be honest I can't see how that's a good idea. Having the return line plumbed to dump right back into the main supply line that is being pumped out of the tank by the electric fuel pump. I could see some serious issues there, especically if the fuel pump decides to start siphoning off the return line rather than the tank.

Don S,
Your method looks like a valid course of action but it sure seems like a lot of work when I could just buy the sender I linked to above that already has a return line fitting on it. It's not really that expensive all things considered.

If you look closely at the sending unit I'm looking at buying you can see that it has a return line fitting already made into it

Re: Fuel injection fuel line return fitting options

That is fine too.
I must admit though, I never seen one with a return fitting before.

Re: Fuel injection fuel line return fitting options

To be honest I can't see how that's a good idea. Having the return line plumbed to dump right back into the main supply line that is being pumped out of the tank by the electric fuel pump.

Click to expand...

Which pump would that be? There are mechanical lift pumps (and some electric) as well mounted on the engine, but there's no pressure pumps inside of boat gas tanks. Nadda, nil, not in a million years are there pumps inside of fuel tanks.

My method works just fine as long as you don't have an air leak in the system, especially in the return side. If you do the pump is going to suck bubbles and you'll have all sorts of problems with the EFI system.

Honestly I didn't even notice the link you posted the first time. I"ve never seen that product before, with the return fitting, but it looks like that product will work just fine too.

Just make sure your tank vents are clear. Get in the habit of checking them every once in a while.

Re: Fuel injection fuel line return fitting options

Don S said:

I must admit though, I never seen one with a return fitting before.

Click to expand...

Me either. I found it by accident today while shopping for a new sending unit. Almost makes me wonder if the leaky sending unit wasn't a huge blessing in disguise

Re: Fuel injection fuel line return fitting options

Don S said:

That is fine too.
I must admit though, I never seen one with a return fitting before.

Click to expand...

Me either, That is a pretty cool idea, looks clean and safe to me.

Re: Fuel injection fuel line return fitting options

JustJason said:

Which pump would that be? There are mechanical lift pumps (and some electric) as well mounted on the engine, but there's no pressure pumps inside of boat gas tanks. Nadda, nil, not in a million years are there pumps inside of fuel tanks.

Click to expand...

Wasn't implying that there was a pump in the tank

I'm referring to the electric pump I have that is mounted on the opposite side of the bilge.

I still say that's going to cause problems. On one hand the pump is supposed to be lifting/siphoning/however you want to say it.. the fuel from the tank. Now we're adding another line coming from the fuel rail return. I can't see how that would be good.

Re: Fuel injection fuel line return fitting options

but there's no pressure pumps inside of boat gas tanks. Nadda, nil, not in a million years are there pumps inside of fuel tanks.]

Jason just so you know, Mastercraft boats has been putting the fuel pump in the fuel tank for a few years now, I forget how long but it been some time now.

All the Mastercraft service dealers hate them from what i have heard, Also it is vary important that you do not run the boat out of fuel or you will be buying a new fuel pump every time you do they say.

Click to expand...

Re: Fuel injection fuel line return fitting options

Interesting BT... I Admit i've never seen that either. I've never worked on Mastercrafts and whatever/Indmar/PCM??? they are using for engines though. I'm more of a Merc guy and a Mercury/JRude/Yamaha OB guy. That's 99%of what I work on.

I take my quote back then.... But I will still say in 99% of boats there are no fuel pumps inside of the tank

Re: Fuel injection fuel line return fitting options

A regular EFI system will have vaporlock issues if you recirculate the fuel that way. the fuel would just go around in a big loop from the fuel rail to the pump through the filter,etc... the heat from the pump as well as the ambient heat from the engine would heat the fuel to the point of it turning to vapor, and you would have vaporlock. As soon as you shut the boat down for 20 minutes or so and go to restart it, you will regret setting it up that way.

That fuel sender with return looks like a perfect solution to you're problem.


When I added my return though, it was rather painless. Mind you, I had my tank out of my boat.

Just make sure if you're using NPT fittings and fuel to use the proper sealant.

Re: Fuel injection fuel line return fitting options

mylesm260 said:

A regular EFI system will have vaporlock issues if you recirculate the fuel that way. the fuel would just go around in a big loop from the fuel rail to the pump through the filter,etc... the heat from the pump as well as the ambient heat from the engine would heat the fuel to the point of it turning to vapor, and you would have vaporlock. As soon as you shut the boat down for 20 minutes or so and go to restart it, you will regret setting it up that way.

Click to expand...

That's basically what I was trying to say

While we're on the subject. What exactly are the standards for hard lines and flexible lines. I'd like to have custom high pressure hoses with crimped fittings made up for the entire system so I can just be done with it.
I remember reading somewhere about specific Coast Guard regulations on fuel lines.