Portable fuel tank

[Paul and Judy]

I have to move my hunter 33.5 from the marina to a friends dock. My problem is my diesel tank is damaged and will not hold fuel. I would like to purchase a 3 gallon portable gas fuel tank and have the following questions:

Can I put diesel in a portable tank designed for gas temporarily

I know gas tanks do not have a return line and would it work ok if I added the existing return line currently feeding the damaged diesel tank.


Thanks is advance.

 

[dlochner]

Yes you can put diesel in a gasoline tank. Any traces of diesel left in the tank should not affect its use as a gasoline tank. Remember, that many small gas engines burn an oil gas mixture and diesel is somewhere between oil and gasoline in combustibility. A 3 gallon tank holds 384 ounces of fuel, with 4 ounces of diesel left in the tank, it would only be a 100:1 ratio.

How far do you have to motor the boat? How much fuel is pumped by the fuel pump? It might be best to modify the gas tank to accept a return fuel line. If the fuel pump puts out 1 gallon a minute, the tank will be empty before you get out of the slip. The return doesn't have to be fancy, just poke a hole in the top of the container and stick the hose in it. Just make sure it doesn't come out while the engine is running.

 

[Paul and Judy]

The engine is a 27 hp diesel and consumes about 1/2 a gallon per hour at 6-8 knots. The distance I need to go is about 2 miles, so I should be ok for fuel. Thanks for the quick response.

 

[kloudie1]

One "quick and dirty" would be to put a tee in the fuel supply line on the tank side of the hand pressure bulb so that overflow goes to engine or tank.. just be sure that all air is bled out before connecting the overflow to the tee..

 

[dlochner]

The engine is a 27 hp diesel and consumes about 1/2 a gallon per hour at 6-8 knots. The distance I need to go is about 2 miles, so I should be ok for fuel. Thanks for the quick response.

The key question is the flow rate for the fuel pump. While the engine only burns a half gallon an hour the flow rate for the pump may be as high as 20 or 30 gallons per hour. That's why the return needs to go back to the fuel tank. At 6 knots, that's a 20 minute or so trip. The engine will pump 6 to 10 gallons of fuel while only burning a quarter gallon.

 

[Paul and Judy]

Do you think three gallon tank will be big enough??

 

[dlochner]

For a 30 minute trip, 3 gallons will be big enough if the fuel return goes back to the tank that the fuel is being drawn from. If the return fuel goes elsewhere, then no it is not.

In order to get enough pressure to spray fuel into the cylinder through the fuel injectors, a high volume pump is used to create the pressure with a very tiny hole for the fuel to spray out into the cylinder. The excess fuel is then returned to the tank to be pumped out again. Think of a garden hose with a very tiny leak. There is a small stream of water that comes out and the rest goes out the end of the hose. Same principle, lots of volume and a tiny hole.

 

[Paul and Judy]

Thanks
Three gallons it will be

 

[jssailem]

Find a place on the boat to secure the tank and the fuel lines. Do not want them to tip over or pop out spraying diesel all over the place. One of those milk crate like baskets always works for me.

 

[SOCAL C50]

Yes, make sure return line goes to the same tank. Do let it run for awhile to make sure the return line is pumping fuel back into the temp. tank.

 

[Gunni]

Interesting concept. Seems like you would want a larger tank (5 gal, half full) and a vent. I would want it lashed above deck because diesel fumes below deck are not good.

 

[centerline]

The key question is the flow rate for the fuel pump. While the engine only burns a half gallon an hour the flow rate for the pump may be as high as 20 or 30 gallons per hour. That's why the return needs to go back to the fuel tank. At 6 knots, that's a 20 minute or so trip. The engine will pump 6 to 10 gallons of fuel while only burning a quarter gallon.

correct..... dont overlook the fact that it needs a return line. a person cant just cap the return line and think it will be ok for awhile because it wont. without the return line working, the injectors will stop injecting metered amounts of fuel into the engine and it will act like its out of fuel, only with a lot of smoke and possibly some damaging preignition.
the speed that the fuel is being drawn from the tank to the pump, and then returning back to the tank is about 2-3 gallons per minute... with a very small amount (about 6 teasp) being used by the engine in that minute..... so 3 gallons will be enough to make the trip as long as the return fuel can cycle back into the container where the fuel pick-up line is, to be sucked up again.... the diesel fuel just keeps going around in a circle thru the system, until it is eventually all used up at a rate of about 6-7 teaspoons per minute...

 

[heritage]

From www.yanmarhelp.com:
The total engine fuel flow, on a 3GM30 ( 27hp ) is not much greater than the engine fuel consumption as the return flow is low.

This is from a Yanmar tech several years ago and the link no longer works. The reason I was researching the ratio of fuel use to total fuel flow was I noticed that on my 2gm at idle I was getting only a couple of drops after several minutes of idling. Most engines do have a higher ratio. As I recall the Volvos were more like one gallon burned, two gallons returned.

 

[centerline]

From www.yanmarhelp.com:
The total engine fuel flow, on a 3GM30 ( 27hp ) is not much greater than the engine fuel consumption as the return flow is low.

This is from a Yanmar tech several years ago and the link no longer works. The reason I was researching the ratio of fuel use to total fuel flow was I noticed that on my 2gm at idle I was getting only a couple of drops after several minutes of idling. Most engines do have a higher ratio. As I recall the Volvos were more like one gallon burned, two gallons returned.

yes...
it really depends on the system design.. some do have a low return flow and some a much higher rate of flow... but no matter what the return rate is, it cannot be restricted from returning as freely as it wants to.

 

[Benny17441]

yes...
it really depends on the system design.. some do have a low return flow and some a much higher rate of flow... but no matter what the return rate is, it cannot be restricted from returning as freely as it wants to.

Yes, but if it is low flow it may not have to be returned to the same can. For temporary use a low flow return can be collected in perhaps a more conveniently located and smaller receptacle.

 

[dlochner]

Yes, but if it is low flow it may not have to be returned to the same can. For temporary use a low flow return can be collected in perhaps a more conveniently located and smaller receptacle.

This would work, but it is necessary to know what the return fuel flow is and have enough fuel in the tank to get where you're going. He's planning on going 2 miles, so at best he'll run the engine for about an hour or less and since the engine burns ¾ gallon an hour, a 2 or 3 gallon supply is all that is necessary if the fuel is returned to the tank.