Run Merc 3.0LX on external fuel tank

[MikeDobbs]

Hello all. Is it possible to run a Mercruiser 3.0lx engine on an external tank (like outboards run on)? I've had issues every season with my carb getting gummed up, and I'd like to eliminate the tank from the loop for troubleshooting and less hassle for now.
I just want to be sure this is safe to do, and will allow the engine to operate normally.

I'm thinking I'd just run the line out of the external tank to the inlet side of my inline fuel filter/water separator.

Thanks in advance.

I'm thinking of something like this: External Tank

 

[matt167]

It can’t have a primer bulb. But I think as long as you have the non permeable line below deck, you’ll be legal.

 

[MikeDobbs]

It can’t have a primer bulb. But I think as long as you have the non permeable line below deck, you’ll be legal.

Thanks for the response. This may be a stupid question, but if the line (and therefore tank) are below deck, wouldn't that allow fuel vapor to escape the tank below deck? Obviously the blower should pull that out, but I was thinking it should be located above deck in the open air.

 

[matt167]

The line inside of the bilge area needs to be the non permeable type. Yes the tank needs to be above deck

 

[cyclops222]

Do you put any type of fuel additives into your gas tank ? If yes. They can cause that type of problem. Do you put in more than 1 type / brand ?

 

[Chris1956]

Mike, run the fuel line from the separator to the tank. To be legal, you would need an antisiphon valve on the fuel tank, but those portables usually do not have them. A primer bulb is necessary, BTW.

Since this is only a test, I would not sweat the A-S valve. Do remember to plug the fuel pickup on the built in tank and run the blower before starting the motor.

 

[matt167]

Primer bulb isn’t any more necessary than with an inboard tank. The line will hold enough fuel to get it running. They are prohibited on inboard installations

 

[Chris1956]

If he has an electric fuel pump the primer bulb is unnecessary, however, if he has a mechanical fuel pump, a primer bulb will prime the pump and perhaps the carb, allowing the motor to start faster. Since this is for a test, vs conventional use, that could be an advantage.

 

[Scott Danforth]

If he has an electric fuel pump the primer bulb is unnecessary, however, if he has a mechanical fuel pump, a primer bulb will prime the pump and perhaps the carb, allowing the motor to start faster. Since this is for a test, vs conventional use, that could be an advantage.

still not legal on an I/O, and the mechanical pump will suck fuel over 22 feet. so not needed.

 

[MikeDobbs]

Do you put any type of fuel additives into your gas tank ? If yes. They can cause that type of problem. Do you put in more than 1 type / brand ?

I put Startron in with every tank to combat Ethanol Fuel (non-ethanol fuel is basically non-existent where I live). The boat was 20 years old when I got it, so I have no idea what may have been used before. I have not heard of Startron causing issues before- in your experience can that cause problems?

 

[MikeDobbs]

Mike, run the fuel line from the separator to the tank. To be legal, you would need an antisiphon valve on the fuel tank, but those portables usually do not have them. A primer bulb is necessary, BTW.

Since this is only a test, I would not sweat the A-S valve. Do remember to plug the fuel pickup on the built in tank and run the blower before starting the motor.

You're saying to just eliminate the fuel filter and run the tank directly to the fuel pump? I was thinking I should keep the fuel filter in the mix since I can't avoid Ethanol fuel here. I was planning to simple plug the fuel line coming from the tank to the filter- are you saying I need to access the fuel pickup and plug that directly? I have a mechanical filter on the block, so I figured I didn't need to mess with the tank other than plugging the fuel line at the filter.

My hope is to be able to run this setup for a few weeks with a new rebuilt carb to convince myself that it's worth the time/expense to try to replace the built in tank if that's what's causing the issues.

I was planning to leave the primer bulb in the mix to prime the line to the pump (mechanical), and also to prevent fuel draining back down the line into the tank.

 

[tank1949]

Hello all. Is it possible to run a Mercruiser 3.0lx engine on an external tank (like outboards run on)? I've had issues every season with my carb getting gummed up, and I'd like to eliminate the tank from the loop for troubleshooting and less hassle for now.
I just want to be sure this is safe to do, and will allow the engine to operate normally.

I'm thinking I'd just run the line out of the external tank to the inlet side of my inline fuel filter/water separator.

Thanks in advance.

I'm thinking of something like this: External Tank

UR tank may have been compromised or your hose vent is toast. UR water fuel separator should have an additional input and output hose barb connection (may have to install). I have fuel tank selector switches in mine in addition to the fuel separators.

 

[MikeDobbs]

UR tank may have been compromised or your hose vent is toast. UR water fuel separator should have an additional input and output hose barb connection (may have to install). I have fuel tank selector switches in mine in addition to the fuel separators.

Yes it does- I could use the extra input to plumb the separate tank, but I figured it was easier to just pull the existing line so I don't have to install a fuel selector switch

 

[Chris1956]

Mike, I think you should connect the aux tank to your water separator. Although ethanol fuel is not the devil alot think, it still benefits from a good filtering before use.

Are you going to clean your carb before you try this test?

Carbs usually get gummed up if you leave them full of fuel and don't use the boat. Is that what the scenario is?

 

[MikeDobbs]

Mike, I think you should connect the aux tank to your water separator. Although ethanol fuel is not the devil alot think, it still benefits from a good filtering before use.

Are you going to clean your carb before you try this test?

Carbs usually get gummed up if you leave them full of fuel and don't use the boat. Is that what the scenario is?

I do have a rebuilt carb I can put on before hooking up tan external tank. I haven't started the boat yet this season due to an injury, but am going to get her going this week.

The carb has been an ongoing issue- I've never made it through a season without having to replace/rebuild a carb. I've got a couple weeks before leaving for a trip and would like to get some use out of the boat. Considering two options at the moment:

1) Plumbing a second fuel filter/water separator and changing them more frequently in an attempt to keep gunk from reaching the carb

2) Plumbing the external tank as we've been discussing to eliminate the tank completely (for now)

 

[Scott06]

I do have a rebuilt carb I can put on before hooking up tan external tank. I haven't started the boat yet this season due to an injury, but am going to get her going this week.

The carb has been an ongoing issue- I've never made it through a season without having to replace/rebuild a carb. I've got a couple weeks before leaving for a trip and would like to get some use out of the boat. Considering two options at the moment:

1) Plumbing a second fuel filter/water separator and changing them more frequently in an attempt to keep gunk from reaching the carb

2) Plumbing the external tank as we've been discussing to eliminate the tank completely (for now)

Plumb the external tank into existing fuel filter (change the filter). before putting on the rebuilt carb purge fuel line from new tank to carb into a jar, make sure the fuel is clean.

Could also take a sample off fuel on on carb before you change fuel tanks by pumping into a jar see if there is crud in there. It sounds like either the carbs are not getting fully clean , or you are polluting a clean carb with contaminated fuel.

If you can run it on the external tank with no issues you know you have to remove the fuel from existing tank and clean it out.

 

[Chris1956]

A single water separator should be more than adequate to filter your fuel. A second one will restrict fuel flow and is unnecessary.
Your carb should not get gummed up that often. I rebuilt my MerCruiser carb once in the 10+ years I owned it, and I bought it used. Something is amiss, I would think.

Clean the carb, and try the external fuel tank. It also makes sense to pump the built-in tank dry and examine the fuel for dirt and water. Dirt can be filtered out, water and water+alcohol mix can be poured off. Water and water+alcohol will sink to the bottom of the tank, so siphon the bottom of the tank into a clear container so you can see the stuff. An oz or two of 2 cycle oil will color the fuel so you can see the water and water + alcohol easily.

 

[MikeDobbs]

Plumb the external tank into existing fuel filter (change the filter). before putting on the rebuilt carb purge fuel line from new tank to carb into a jar, make sure the fuel is clean.

Could also take a sample off fuel on on carb before you change fuel tanks by pumping into a jar see if there is crud in there. It sounds like either the carbs are not getting fully clean , or you are polluting a clean carb with contaminated fuel.

If you can run it on the external tank with no issues you know you have to remove the fuel from existing tank and clean it out.

That's my thinking exactly.

 

[MikeDobbs]

A single water separator should be more than adequate to filter your fuel. A second one will restrict fuel flow and is unnecessary.
Your carb should not get gummed up that often. I rebuilt my MerCruiser carb once in the 10+ years I owned it, and I bought it used. Something is amiss, I would think.

Clean the carb, and try the external fuel tank. It also makes sense to pump the built-in tank dry and examine the fuel for dirt and water. Dirt can be filtered out, water and water+alcohol mix can be poured off. Water and water+alcohol will sink to the bottom of the tank, so siphon the bottom of the tank into a clear container so you can see the stuff. An oz or two of 2 cycle oil will color the fuel so you can see the water and water + alcohol easily.

I just want to check I understand what you're saying. It sounds like you're saying I can basically clean/strain the fuel in the tank and put it back; but perhaps you're just suggesting siphoning some from the bottom of the tank to test and see how bad the contamination is?

Are you saying I can siphon the gas out of the onboard tank, strain it to remove any dirt/debris, then add a touch of 2 cycle to color the fuel, and allow to settle a bit. At that point I can siphon off water/alcohol from the bottom of the container (which should be clear), and when I get all of that out I should have good fuel left which I can return to the tank in the boat?

 

[MikeDobbs]

Plumb the external tank into existing fuel filter (change the filter). before putting on the rebuilt carb purge fuel line from new tank to carb into a jar, make sure the fuel is clean.

Could also take a sample off fuel on on carb before you change fuel tanks by pumping into a jar see if there is crud in there. It sounds like either the carbs are not getting fully clean , or you are polluting a clean carb with contaminated fuel.

If you can run it on the external tank with no issues you know you have to remove the fuel from existing tank and clean it out.

When you say "remove the fuel from existing tank and clean it out," do you mean clean out the fuel and return it to the tank, or do you mean clean out the tank?