How to deal with a furnace with a need to bleed

Hi,
This is the second winter in my "new" house -- furnace is approx 15 years old. Runs on oil -- tank is outside in very cold climate, so oil is mixed with kerosene by fuel company. The furnace has an issue in that, as the oil volume in the tank decreases, air seems to sneak into the line. Last year this occurred reliably at 1/4 tank (according to the plastic gauge); this year it has begun to happen with as much as 1/3 tank remaining.
Generally, when I discover that the furnace has stopped running, I can bleed the line for approx. 10 seconds, see the pink oil sputter out air, turn to a richer black color, and close the line. The furnace kicks in and will often run for awhile again (possibly days, if necessary) until at some point air gets into the line again. I sense that as oil volume continues to decrease, the need to bleed becomes more frequent. The problem disappears when the next oil delivery fills up the tank.
This is a one line system. My furnace 'guy' says that a two line system will fix the problem, but he (working alone, and somewhat older) is uncomfortable doing the work in the extreme cold of winter (line runs through a low crawlspace; oil tank and furnace on opposite sides of house).
My questions are (a) is he right? (his price for installing a second line was quite reasonable) and (b) is there *anything* I can do this season to help? Waiting until the furnace stops (often in the middle of the night) to wake up to a cold house is inconvenient to say the least.
thanks! Aaron
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Aaron wrote:

I wonder if the kero mix is part of the problem? A 2-pipe system will likely solve it. What if you pulled the new copper line (even a temp route) and left the final hookup to him?
Jim
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Is the tank at the same level, or lower as the furnac, if so you have an air leak somewhere. Retighten all the fittings and see what happens. Greg
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