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Old 08-28-2017, 11:23 AM   #1
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2 Tanks 1 engine fuel feed question

I have two diesel fuel tanks feeding one engine through a series of valves (Picture attached) that enable me to feed and return the fuel to the engine from either tank, using one of two filters. My question is: Can I feed and return from both tanks at the same time? The reason I ask is that the fuel gauge on one tank is unreliable. It's an 1983 boat and I think the float is waterlogged and there is a beam less than 1" over it with no room to remove the mechanism. Using a weight (1 oz. sinker) & string, I can check the fuel level on that tank by removing a plug on top of that tank. The other tank does not have any extra fittings so I have to rely on it's gauge, which seems to be accurate??? If I feed & return from both tanks, I can always be fairly sure where the fuel level is on both. The engine is a Volvo TAMD40B, cruised at between 16 & 2000 RPM WOT is 3400 RPM.
Does anyone have experience with this situation?

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Old 08-28-2017, 11:27 AM   #2
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You can draw and return to both tanks at the same time. However, it doesn't mean that each tank will draw the same amount. If you full both tank full and draw and return to both, it is possible that the return will be equal but the draw won't be. In this situation depending on how much fuel your engine returns, you can over fill your tank and spill diesel out your vent.

If you can't get at the sender, it would be good to eventually get some other way to check fuel levels. You can look at a Tank Tender as one option. I would also seriously consider adding sight tubes to the tank if you can get at the sides of the tanks.
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Old 08-28-2017, 11:38 AM   #3
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You can draw and return to both tanks at the same time. However, it doesn't mean that each tank will draw the same amount. If you full both tank full and draw and return to both, it is possible that the return will be equal but the draw won't be. In this situation depending on how much fuel your engine returns, you can over fill your tank and spill diesel out your vent.

If you can't get at the sender, it would be good to eventually get some other way to check fuel levels. You can look at a Tank Tender as one option. I would also seriously consider adding sight tubes to the tank if you can get at the sides of the tanks.
Both tanks (100 Gals. ea.) are about 3/4 full now. I know the port is, checked with a string. I would love to add sight tubes, I can get at the sides, but I would have to empty the tanks to do that or to add any fitting. What is a tank tender? Do you have to have a hole in the tank to add it?
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Old 08-28-2017, 11:40 AM   #4
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Fuel management with your system shouldn't be too difficult. Your TAMD40 has a modest fuel pump, so the refilling that occurs from the return line is slow. Just get in the habit of always setting the return to the tank that is in use. Change tanks (for both feed and return) whenever the trim gets noticeably off level.

I wouldn't trust leaving the return on both tanks, as there is never a guarantee that pulling from both will evenly deplete your tanks, nor is there any guarantee a return will be truly balanced.
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Old 08-28-2017, 11:44 AM   #5
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Would be good to see your valve arrangement, you can attach by scrolling down on this page near to the bottom and click on Manage Attachments, a box will open on the left side click on manage attachments/go to your picture (be sure it's not to big-(you may have to down size first) click on open then wait for it to upload then click on attach,

Back to your question, if both of your tanks are connected at any point in the system to the engine through a valve or tee piece or what ever then they will equalize (may take a little time-minutes) and if equalized then it makes no difference what tank your return line goes to as over a few minutes will again equalize,

The rule is if using port tank the return must be to the port tank and vica-versa

The return on 90% of diesels is a minimal issue( some Like GM'S pass as much as they use -some times more-) so on these applications it's more critical to be sure which tank is being returned to

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Old 08-28-2017, 11:50 AM   #6
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I neglected to say assuming both your tanks are the same installed height /size
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Old 08-28-2017, 11:52 AM   #7
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Would be good to see your valve arrangement, you can attach by scrolling down on this page near to the bottom and click on Manage Attachments, a box will open on the left side click on manage attachments/go to your picture (be sure it's not to big-(you may have to down size first) click on open then wait for it to upload then click on attach,

Back to your question, if both of your tanks are connected at any point in the system to the engine through a valve or tee piece or what ever then they will equalize (may take a little time-minutes) and if equalized then it makes no difference what tank your return line goes to as over a few minutes will again equalize,

The rule is if using port tank the return must be to the port tank and vica-versa

The return on 90% of diesels is a minimal issue( some Like GM'S pass as much as they use -some times more-) so on these applications it's more critical to be sure which tank is being returned to

Cheers Steve
Thank you all for your comments. Picture of valves is now on my first post. Port tank has red tape, Stbd. green. The return comes up to the top in-between the red & green Valves.
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Old 08-28-2017, 11:54 AM   #8
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I have a single engine with two tanks. For a while I ran with both valved in so in theory the tanks should draw down equally. This worked fine until it did not!! Stalled the engine and found one tank bone dry and the other nearly full. Something to do with a air pocket in the return line favoring one tank vs the other.

So now I run on one tank, then run on the other, but not both.

Fortunately I can dipstick my tanks so I reliably know the levels.

Only way to reliably share tanks is if you have a cross tie line tapped into the BOTTOM of the tanks. And even that has issues that can screw up vessel trim.

Simplest to just run on one, at end of day switch to the other.
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Old 08-28-2017, 11:58 AM   #9
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Quote:
Originally Posted by 1Sailor View Post
Both tanks (100 Gals. ea.) are about 3/4 full now. I know the port is, checked with a string. I would love to add sight tubes, I can get at the sides, but I would have to empty the tanks to do that or to add any fitting. What is a tank tender? Do you have to have a hole in the tank to add it?
Hart Systems - Home

You do have to add a small hole in the top of the tank to add it.

Now I am curious, the company President is named Ron Hart. When I was a kid we sailed with a Ron Hart. We had a San Juan 24 at the time and Ron and his wife had an Erickson 27. Hart Systems Inc, is located in Gig Harbor now but I believe was in Lakewood before then, which is where the Ron Hart that I knew lived back in they day....

Likely just a coincidence.
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Old 08-28-2017, 11:58 AM   #10
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I neglected to say assuming both your tanks are the same installed height /size
Both tanks are the same size & same height, but the feed & return come up to or a little higher than the height of the top of the tanks & feed & return on the top of the tanks.
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Old 08-28-2017, 12:08 PM   #11
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The levels of each tank can be read with an infrared temperature gun. The fuel will be either warmer or cooler (season) than the head space above the fuel. Or install sight tubes.
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Old 08-28-2017, 12:52 PM   #12
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As to accuracy of fuel guages, I have none, so no comment. I fill when my hour meters tell me to, knowing my per hour consumption.
I had a pair of TMD40s originally, used about 2 GPH per engine. I fill after 50 to 75 hrs, so usually see a small difference between the tanks, as one also feeds the genset and the other also feeds the diesel stove. One or other may get more use between fills.
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Old 08-28-2017, 05:56 PM   #13
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As to accuracy of fuel guages, I have none, so no comment. I fill when my hour meters tell me to, knowing my per hour consumption.
I had a pair of TMD40s originally, used about 2 GPH per engine. I fill after 50 to 75 hrs, so usually see a small difference between the tanks, as one also feeds the genset and the other also feeds the diesel stove. One or other may get more use between fills.

Thank you all for your helpful inputs.http://www.trawlerforum.com/forums/i...lies/smile.gif

I Have an infrared temp meter & I'll try that. & I will watch the hour meter & mark down the hours when I fill full to winterize. I also figure about 2 GPH +-. I'll know better after I fill a couple of times. Also I have the string with the sinker for the port tank. The string & sinker also tells me that the fuel in the tank is clean & no sludge on the sinker when I bring it up.
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Old 08-28-2017, 07:51 PM   #14
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Yes you can run from both tanks. That's how my last boat was. At the end of a days run, if a slight list was noted, I would adjust the return valve so it wouldn't return quite as much to the heavy tank. After some experience, you will learn how to have the valves set. Previously it was adjusted by partly closing one supply valve and keeping the return valves wide open. I preferred adjusting it with the return.
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Old 08-28-2017, 08:26 PM   #15
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Have a single engine and four fuel tanks of about 79 gallons each. Tanks are located port and starboard. Take fuel from one tank at a time and return to same. Switch tanks about every eight hours to keep on an even keel. Have a gauge that measures fuel in individual tanks. Works for me, and haven't run out of fuel yet.
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Old 08-28-2017, 10:07 PM   #16
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I have the same setup as you-2-100 gal tanks-one TAMD40B engine. Except I have one Racor fuel filter. One fuel gauge on starboard tank. I run on both tanks and return to both tanks. No problems after a couple of years. Always within a couple of gals. per tank at fill up. Boat stays level.
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Old 08-29-2017, 07:15 AM   #17
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To simplify the system a fuel valve that select a tank and return fuel to the selected tank is not expensive.

A simple log can equalize the hours on each tank .

And keeping track of gallons installed at fuel stops will show if one engine is more thirsty than the other.
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Old 08-29-2017, 07:49 AM   #18
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Quote:
Originally Posted by 1Sailor View Post
I have two diesel fuel tanks feeding one engine through a series of valves (Picture attached) that enable me to feed and return the fuel to the engine from either tank, using one of two filters. My question is: Can I feed and return from both tanks at the same time? The reason I ask is that the fuel gauge on one tank is unreliable. It's an 1983 boat and I think the float is waterlogged and there is a beam less than 1" over it with no room to remove the mechanism. Using a weight (1 oz. sinker) & string, I can check the fuel level on that tank by removing a plug on top of that tank. The other tank does not have any extra fittings so I have to rely on it's gauge, which seems to be accurate??? If I feed & return from both tanks, I can always be fairly sure where the fuel level is on both. The engine is a Volvo TAMD40B, cruised at between 16 & 2000 RPM WOT is 3400 RPM.
Does anyone have experience with this situation?

I'm having trouble attaching a photo. I can e-mail one to anyone who wants to see it.
Hi

Or new measuring sensors for surface mounting in the tank
Products - Gobius

If your Volvo is 160hp version is consumption about WOT 9,2 gal/hour and cruise 2000rmp about 5,2 gal/hour (botom clean and right sitze propel)

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Old 08-29-2017, 08:49 AM   #19
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I have single engine and two 50gal tanks same height.

I always run off one tank and return to same. I do have installed pipe plugs on top of each tank. I dip w wood stick to check amount of fuel. At 1gph I know very close to how much I burn from a tank. Switch as needed for port/stbd trim.
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