Using a Boat Fuel Tank Externally to Carb to run engine

slshearer

slshearer

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Jun 13, 2024
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Hello

Not sure anyone can help me but here it goes, I need to drain and dispose of both the main and reserve fuel that is 6 years old, I filled my tanks with fresh gas and added fuel conditioner before I put the unit into covered storage, I ran the RV 3 years ago and it started right up and ran fine for about 15 minutes. I was thinking of draining the tanks using the generator gas line unitil the tanks were empty which I understand will still have some fuel left in the tanks.

I am planning on running the engine temporariy using a boat style portable gas tank that holds 6 gallons and has a return line as well as a supply line.

My Plan is to disconnect the main fuel line to the fure pump but will I damage the fuel pump if I run the engine with no gas line attached?

I plan to drain the tanks using a electric fuel pump at the generator gas line into several gas storage containers to dispose of the old gas,

Has anyone drained their tanks by this method and then addded fresh gas to the old? What was the experience...

Also on the carb I have been told to put some injector cleaner down the middle of the carb to remove any possible gum that may have developed, My thought was to do this as well as in the external fuel tank I plan to use to run the engine initially.

Your information is much appreciated and Thank you for you help!
Stewart
 
How far do you plan on driving on the boat tank? Does it have its own pump? You could potentially plumb the boat tank to the input of the mechanical fuel pump if you want to keep it connected.

The mechanical fuel pump is pretty simple--just a diaphragm that oscillates back and forth, and essentially check valves at the input and output. I woudn't think running it without gas for a while would be damaging. Maybe a long-term issue, but if you're just trying to move the coach across town or get to a gas station, I'd think it's a non-issue.

If you did decide to disconnect the input on the mechanical fuel pump, however, you could kill two birds with one stone. This gives you access to the line needed to drain both tanks, without leaving 1/4 tank of bad gas in each one. Diluting 1/4 tank of bad gas with 3/4 tank of good gas will probably leave you with a coach that runs OK, but I'd rather just get all the old stuff out.
 
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pvfjr said:
How far do you plan on driving on the boat tank? Does it have its own pump? You could potentially plumb the boat tank to the input of the mechanical fuel pump if you want to keep it connected.

The mechanical fuel pump is pretty simple--just a diaphragm that oscillates back and forth, and essentially check valves at the input and output. I woudn't think running it without gas for a while would be damaging. Maybe a long-term issue, but if you're just trying to move the coach across town or get to a gas station, I'd think it's a non-issue.

If you did decide to disconnect the input on the mechanical fuel pump, however, you could kill two birds with one stone. This gives you access to the line needed to drain both tanks, without leaving 1/4 tank of bad gas in each one. Diluting 1/4 tank of bad gas with 3/4 tank of good gas will probably leave you with a coach that runs OK, but I'd rather just get all the old stuff out.
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Hello, Thank you for your advise. The boat external gas tank I am going to use works on this principal

An external portable boat gas tank is a convenient way to store and transport fuel for your boat. Here's how it works:
  1. Positioning the Tank: Place the tank in a safe, convenient location outside the boat cabin, away from any sources of heat or flames.
  2. Connecting the Fuel Line: Attach one end of the fuel line to the tank and the other end to the fuel inlet on your boat's engine.
  3. Turning on the Vent: Most portable gas tanks have a vent to release excess air pressure. Turn on the vent to prevent pressure buildup1.
  4. Priming the Fuel Line: Squeeze the bulb on the fuel line to prime it, ensuring fuel flows smoothly.
  5. Starting the Engine: Start your boat's engine and let it idle for a few minutes to ensure proper fuel flow.
 
slshearer said:
Hello, Thank you for your advise. The boat external gas tank I am going to use works on this principal

An external portable boat gas tank is a convenient way to store and transport fuel for your boat. Here's how it works:
  1. Positioning the Tank: Place the tank in a safe, convenient location outside the boat cabin, away from any sources of heat or flames.
  2. Connecting the Fuel Line: Attach one end of the fuel line to the tank and the other end to the fuel inlet on your boat's engine.
  3. Turning on the Vent: Most portable gas tanks have a vent to release excess air pressure. Turn on the vent to prevent pressure buildup1.
  4. Priming the Fuel Line: Squeeze the bulb on the fuel line to prime it, ensuring fuel flows smoothly.
  5. Starting the Engine: Start your boat's engine and let it idle for a few minutes to ensure proper fuel flow.
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So it sounds like they're assuming either the engine has a pump, or it's a gravity-feed situation. The primer bulb is great for getting it started, but something needs to take over. If you mount it up high in the cab, you might get gravity to do the job. Lot's of folks have lashed boat tanks onto the front bumper, and it is nice to get the gasoline out of the cabin. Gravity won't do the trick in that case.

In either scenario, it would work well to run the boat tank to the input of the engine's mechanical fuel pump. Or, you could use the electric pump once you're done draining the tanks with it.
 
Most likely you are going to replace all the rubber gas hose anyway. Either find a convenient gas line end to disconnect and connect the electric pump to empty the tanks or just find a spot three four feet after the switching valve from front to rear tanks and just plumb up the electric pump there. I wouldn't mess with running the generator to get rid of the gas.

I drove a motor home 13 miles with a gas tank in front of passenger seat and installed the fuel pump to the underside of the hatch which was leaned up against the dash. A bit noisy but, I could keep an eye on the engine too.
 
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Bhart said:
Most likely you are going to replace all the rubber gas hose anyway. Either find a convenient gas line end to disconnect and connect the electric pump to empty the tanks or just find a spot three four feet after the switching valve from front to rear tanks and just plumb up the electric pump there. I wouldn't mess with running the generator to get rid of the gas.

I drove a motor home 13 miles with a gas tank in front of passenger seat and installed the fuel pump to the underside of the hatch which was leaned up against the dash. A bit noisy but, I could keep an eye on the engine too.
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Hello

Did you have a fuel pump or was it gravity fed? Did you disconnect the mechanical fuel pump? Thank you Stewart
 
I think you are making this more difficult that necessary. Disconnect the rubber gas hose between the front crossover frame and the input of the mechanical fuel pump. All gasoline in the line will flow backwards to the tank(s). Fill a 5 gallon can with gas and mount it in the right side of the front bumper. Bungee it in place. It takes about 6 feet of 5/16" or 3/8" gas line and connect it to the input side of the pump. Run the other end into the tank Use a cable tie ir small rubber bungee to keep the hose from falling out. You are good to go for about 45 miles. I have done this many times . The longest was about 665 miles from Mass. to Central indiana
 
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Ken B said:
I think you are making this more difficult that necessary. Disconnect the rubber gas hose between the front crossover frame and the input of the mechanical fuel pump. All gasoline in the line will flow backwards to the tank(s). Fill a 5 gallon can with gas and mount it in the right side of the front bumper. Bungee it in place. It takes about 6 feet of 5/16" or 3/8" gas line and connect it to the input side of the pump. Run the other end into the tank Use a cable tie ir small rubber bungee to keep the hose from falling out. You are good to go for about 45 miles. I have done this many times . The longest was about 665 miles from Mass. to Central indiana
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I've done this as well, for some reason mine had a second line returning fuel to the tanks. So it pumped my 5 gallons pretty quickly to the rear. Solution was to cut the second tubing and place that in the 5 gallon tank on the front bumper as well.

I drove it about 200 miles this way.
 
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The only thing wrong with this is you have to stop every 45 miles or so to change or refill the 5 gallon container.
 
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I would guess the fuel pump would hold no more than a quarter cup, or 0.015625 gallons. Realistically it's probably a lot less. Why do you ask?

Or is this a volume per stroke question pertaining to the internal design of the pump?

Or is it a flow rate question, inquiring how many gallons per hour it flows? That would depend on the engine RPM, unfortunately.
 
pvfjr said:
I would guess the fuel pump would hold no more than a quarter cup, or 0.015625 gallons. Realistically it's probably a lot less. Why do you ask?

Or is this a volume per stroke question pertaining to the internal design of the pump?

Or is it a flow rate question, inquiring how many gallons per hour it flows? That would depend on the engine RPM, unfortunately.
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Hi

I have a question: If I disconnect the fuel line from the carburetor and let the engine run, how much fuel will be pumped out if I run the engine for about 5 to 15 minutes? I plan to direct the old gas into an external gas canister for disposal, use an external gas tank to fuel the engine and drain the main fuel tank.

Thank you!
 
slshearer said:
Hi

I have a question: If I disconnect the fuel line from the carburetor and let the engine run, how much fuel will be pumped out if I run the engine for about 5 to 15 minutes? I plan to direct the old gas into an external gas canister for disposal, use an external gas tank to fuel the engine and drain the main fuel tank.

Thank you!
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I'm a little confused by this... Are you meaning to use the mechanical fuel pump to pump out gas from the tanks? It won't run very long with just the gas in the carb bowl. I would just use an electric pump to empty the tanks.
 
werewilfs said:
I'm a little confused by this... Are you meaning to use the mechanical fuel pump to pump out gas from the tanks? It won't run very long with just the gas in the carb bowl. I would just use an electric pump to empty the tanks.
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Hi, disconnect the fuel line at the carb and hookup an external electric pump and portable gas tank hooked up to the carb, run the engine at idle to allow the engines fuel pump to empty the fuel from main and spare gas tank to fuel gas cans. We may just run an electric fuel pump as you suggested, I just wanted to know what the rate of fuel the engines fuel pump volume would be. Thank you for your help.
 
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I drove one coach 2,000 miles and another 500 miles, both with a 12 gallon boat gas tank under the dinette. I used an electric pump as I didn’t trust the old mechsnical pump as both coaches had been sitting ten years. Stopped every 90-100 miles. Worked fine. I just drilled a hole in wood step and stuch fuel line through there and onto carb. I used fire sleeve over fuel line where it was on top of the engine. Ordered tank from Amazon and it was waiting when I went to get motorhome. Dont by Edelbrock electric pumps though, they are shite.
 
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AlphaFloor said:
I drove one coach 2,000 miles and another 500 miles, both with a 12 gallon boat gas tank under the dinette. I used an electric pump as I didn’t trust the old mechsnical pump as both coaches had been sitting ten years. Stopped every 90-100 miles. Worked fine. I just drilled a hole in wood step and stuch fuel line through there and onto carb. I used fire sleeve over fuel line where it was on top of the engine. Ordered tank from Amazon and it was waiting when I went to get motorhome. Dont by Edelbrock electric pumps though, they are shite.
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Hi Great to know!!! appreciate your help! Stewart
 
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