Dual oil tanks took less oil than expected

somersny

We have two 275-gallon oil tanks in our basement. Gauge is on the 2nd tank. On Monday, gauge was a hair under 1/2 full, so ordered 250 gallons of heating oil. Delivery received today and receipt identifies only 140 gallons delivered but gauge is now back to full tank.

Any ideas as to what could cause the discrepancy?

EBEBRATT-Ed

Even though the tanks hold 275 gallons some air space is always in the top. The vent whistle in the tank sticks down in the tank so when the whistle stops sounding the oil man shuts the oil off.

A single 2 75 you usually get about 230 in it. With your twinned with one vent I would guess the most oil you have is about 500 gallons total. This is normal. Plus the oil is pumped into the tank at high velocity this causes foam until it settles.

I am assuming your burner line connects to both tanks equalizing across the bottom

somersny

Thank you - that's helpful. I was unfamiliar with the details you mentioned. In the past, my estimations of how much oil the tanks would take based on the gauge were not nearly as far off as they were today when I assumed about 250 gallons but ended up with about 60% of that so was concerned that there may be an issue with the level of oil between the tanks not being comparable.

STEVEusaPA

It's possible the first tank was already almost full, and the tanks aren't equalizing. Although piped correctly (yours is not) that is a legal set up, I'd rather have 2 fills, teed vent, two gauges.
And it appears you have a leak on the cross over union to boot.

somersny

There's no leak, thankfully. That tray of kitty litter was there when I bought the property 3 years ago but I never bothered to move it and it's dry showing no sign of oil.

EdTheHeaterMan

There is a possibility that tank #1 (the tank with the fill pipe) is not draining equally. If a valve is closed at the bottom, if the bottom outlet is plugged with sludge or if the valve has failed (Fir-o-matic handle loose) then tank # 1 will stay full and only tank #2 will feed the burner. This may be a problem that will continue until the summer when you can allow tank #2 to go empty. Then you can use a transfer pump to move the oil from #1 to #2 in order to check the bottom valve of #1 tank.

Right now, you need the heat, and there is no place to put the oil from #1 tank to do a service call on it.

somersny

About 2 1/2 years ago, the pump on our furnace was malfunctioning and we were getting a burning smell from the vents. (The pump that moves the oil from the line into the furnace - I don't recall the specific name of the pump.) Before the technician diagnosed that the pump was beginning to fail, he used a CO2 canister to attempt to blow out the line leading from the tanks in the event the line was clogged and not feeding enough oil to the furnace. That said, if the tanks are not draining equally, possible that asking a technician to again blow out the line could be a first step?

EdTheHeaterMan

somersny said:

About 2 1/2 years ago, the pump on our furnace was malfunctioning and we were getting a burning smell from the vents. (The pump that moves the oil from the line into the furnace - I don't recall the specific name of the pump.) Before the technician diagnosed that the pump was beginning to fail, he used a CO2 canister to attempt to blow out the line leading from the tanks in the event the line was clogged and not feeding enough oil to the furnace. That said, if the tanks are not draining equally, possible that asking a technician to again blow out the line could be a first step?

That may be one option. I personally am not a fan of CO2 blow out gun for oil line service. I prefer a push pull hand pump where you can feel the pressure change with each pump. Building up pressure and final release of blockage. But that is just me! (and @STEVEusaPA also, I believe)

When I was taught about blocked fuel lines back in the 1970's the service manager taught me the CO2 method. I used it for several years, until I purchased the hand pump for another reason. After that I never opened the CO2 blow out kit ever again. It is still in my garage with some 35+ year old CO2 cartridges collecting dust.

somersny

Thanks - very helpful.