Oil furnace problem, no oil mystery

CordWrangler said:

Well, I went to HF and got the MightVac 8000 and then stopped at Lowes to get fittings. I took the vacuum pump into Lowes and they were helpful in getting the right fittings for my copper pipe. So tomorrow I will give it a test and see what happens. So will this take quite a few "pumps" to see if I can get fuel in the attic. Just trying to get an idea of what to expect.
CW

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It'll probably take a good amount of time, 60 feet is a long distance even at 3/8.

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CordWrangler said:

Question about MityVac. They have about 12 different models. Which model would be best for my situation and testing? Also, PepBoys and AutoZone don't seem to have it on their website. Where else have people bought a MityVac?
Thanks,
CW

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No..not really.
Attach the hose. Start pumping. You will show negative pressure (vacuum) on the gauge. Loosen the nipple and your pressure will go to almost zero...then close it and start pumping to build vacuum again.

The beauty of it is that you will see the air coming up and you will see bubbles coming up through the clear tube and oil dumping into the small container. You know when the air is out and you know if you are loosing vacuum indicating something else is up.

This is the one I have. Has held up for years.

https://www.amazon.com/dp/B00265M9SS/?tag=hearthamazon-20

Could you take the bleeder screw out of your pump and attach the mity vac there?

IIRC the MityVac is capable of something like 25" vacuum...that should be plenty to lift heating oil 8'...now it will take some pumping for sure...a 3/8 line holds ~5.3 cubic inches of fuel per foot. Again, IIRC the MityVac is something like 1 cubic inch per stroke...so a little math puts you at 318 strokes to pull fuel through that 60' line...now, that would be in a perfect world...but I'm saying it will probably take a lot more than that.
Did the gauge ever show any vacuum building? It should have, if not you definitely have a leak.
Did you ever try pressurizing the tank?

If I'm calculating this correctly, it should only take ~7" vacuum to lift that oil 8'...

CordWrangler said:

There is no valve at the tank. It is pulling out the top. I have done maintenance on this furnace for 12 years. Each year that I change the filter, nozzle and screen I would lose prime . Every time when I was done, I would bleed the system and the pump would pull fuel from the tank very quickly. Never been a problem until now.

Here is a picture of the suction and return tubes from inside the tank.

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Having the "in tank" suction and return lines even is old school, but I don't like it. It's good when the system is running, but during the purge sometimes air bubbles return go right back into the supply. I used to make the return an inch shorter than the supply pickup.

Re the "can't re-establish prime", is the new tube bigger than the old tube? Sometimes going larger seems like a good idea, but during the prime the pump has to work harder with a bigger line and that could be the difference. Also, since the old 60' tube had lots of staples or kinks, you may not have been draining back as much as you think and almost lost zero prime.
Have you tried pre-filling the filter cup with oil? The pump is much better at pushing than pulling. Sometimes the oil in the filter cup is grabbed by the pump and pushed down the return, causing much better vacuum on the supply line.
Can you describe in some detail the prior successful methods to prime and bleed the system in the prior 12 years?

I know you must have gotten it resolved by now. Please let us know how the problem was resolved. Even if it was done by a pro.

Needs the bypass plug installed in the pump