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Old 10-12-2008, 12:43   #1
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Furnace fuel problems

My 41’ Morgan Classic has a Volvo forced air furnace in the engine room. It is a great asset in the winter here in Vancouver Island, particularly as I enjoy winter sailing.

Here’s the problem. It runs for a while, then shuts off, starved for fuel. If I start the engine and run it for five minutes the furnace will run again (for about an hour) It gets fuel from the engine side of one of my Racor filters (two in parallel). The little fuel pump in the furnace has to draw fuel out of the tank, through the filter and up to the furnace. I don’t believe it is powerful enough. After the furnace had died I removed the fitting on the fuel line that goes to the furnace and found no fuel in the line. The furnace seems to pull what fuel it can out of the fuel line that goes from the Racor to the engine, then shuts down.
I’m considering
- fitting where fuel line leaves tank so furnace won’t have to pull fuel down, through racor and back up etc. I imagine I would need an in line filter on that.
- fitting where return line goes into tank – but is this line always charged with fuel?

Suggestions? I have attached a diagram that my help.

PS - I really think the engine should have its own dedicated fuel line from the tank, but maybe that is not a big deal.
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File Type: doc Furnace.doc (36.5 KB, 103 views)
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Old 10-12-2008, 13:10   #2
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Some questions come to mind: Did the system as installed stop working, or has it never been reliable?

As drawn, the internal fuel pump on the furnace has to pull fuel uphill whan the fuel tank is less than full. It is quite possible that the internal pump is not rated for this. Do you have specifications on the furnace?

Does the furnace work when the fuel tank is full?

I would NOT use the fuel return line It will actually make no improvement in your situation, and in fact make things worse.

You might end up needing a booster pump to push fuel up to the level of the furnace, but the selection of that pump would depend on the specifications of the furnace for inlet pressure.

Bill
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Old 10-12-2008, 13:40   #3
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Furnace installed by PO. My 1st thought was to add fuel to tank. Problem persisted. Furnace works fine until, as near as I can gather, it uses fuel in lines - I think between racor and engine, then shuts down. Running engine charges fuel lines, furnace works.

i don't mave specs on furnace, boat is a couple of hours away.

My big concern is that where I tap into fuel line i am 'emptying' fuel line and could cause a air lock and yanmar won't start.
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Old 10-12-2008, 14:45   #4
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What fuel pump do you have on the furnace? Is the fuel pump part of the furnace or external. Some are push and some are pull. They both have limits to how much lift they can pull or push.
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Old 10-12-2008, 14:51   #5
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Try using a little day tank at same height as pump to feed furnace and see if that fixes problem
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Old 10-12-2008, 15:11   #6
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First, thanks for all the advice. This website is invaluable.

Thought of day tank, but then I have to fill it. May come to that as I am sure it would completly solve the problem.

Fuel pump is integral to furnace, and is pull type. Just can't pull from main tank, so furnace quits when 'easy' fuel is depleted. That's the fuel, I believe, in fuel line between racor and engine.
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Old 10-12-2008, 15:46   #7
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I dont know your heater. But mine is a Dickerson and has a low pressure pump. It also has a one way flow valve inside the pump. The first time I installed it I had it backward. so check the flow arrow. Also the engine fuel pump will pull a lot more fuel that the heater and may pull the fuel out of the heater supply line. Depending on where it is installed. On your flow chart could you add the fuel pumps for both the heater and engine. That may answer the question.
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Old 10-12-2008, 16:38   #8
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Added the fuel pump locations to the attachment.

I don't the the engine fuel pump is pulling the fuel from the furnace, as the furnace runs while the engine is running, and then afterwards for about an hour. Could it be that the little pump in the furnace is not powerful enought to draw fuel through the racor?
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Old 10-12-2008, 16:48   #9
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My heater is direct connected to the tank. It has an inline filter. Are you sure your heater is supposed to be connected through the Racor?
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Old 10-12-2008, 17:01   #10
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That's one of my questions! It was installed by the PO, and since he sailed the boat mostly in the Carribean he probably didn't use the furnace much.

Is your heater direct connected through a seperate fitting on the tank?
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Old 10-12-2008, 19:30   #11
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Quote:
Could it be that the little pump in the furnace is not powerful enought to draw fuel through the racor?
There has to be a fuel pump some place or the furnace would not work. There also has to be a fuel filter for the fuel to the furnace or it wouldn't stay working for long. It would be best to check the docs on the furnace for installation details. They should say what the limits are for the fuel line.

Being after the racor is not really a bad thing but I would have it with it's own filter not on the engine fuel line. These things only need about 75 - 200 microns filter and do not need the higher level of filtering the engine needs. It wouldn't hurt it but it's not required. The racor should not offer that much resistance. It could be the lift on the pump inside the furnace. You need to check the install manual.
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Old 10-12-2008, 19:57   #12
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Mine goes through the racor fine. If it has not been used a lot, I would pull the line at the heater and see if you can pull under suction with a syringe or pump out a couple of cups of fuel out, maybe sludge of something. Maybe you have a long electric wire run and the pump is not getting enough electricity.
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Old 10-12-2008, 20:37   #13
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Siren came with an Eberspracher from the factory 1976. It has a separate pickup in the tank and a small in line filter. It might just be that the Racor is to fine of filter for the small pump to pull. I am also dubious of the tee system ie: the potential to pull air into the yanmar from a furnace line/fitting failure...It of course would only happen at the worst possible time.
Jim
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Old 10-12-2008, 20:39   #14
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Thanks for all the input, I will b better prepared when I tackle the problem this weekend - weather forecast of -10C.
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Old 10-12-2008, 21:37   #15
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Quote:
Originally Posted by bytownboy View Post
That's one of my questions! It was installed by the PO, and since he sailed the boat mostly in the Carribean he probably didn't use the furnace much.

Is your heater direct connected through a seperate fitting on the tank?
Yeah, it has its own tank fitting.
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