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Heating oil storage tank level gauge accuracy & precision:
How to get an accurate reading of just much oil is in the oil storage tank. How accurate is the oil tank gauge? How should you read an oil tank gauge? Where to get a highly accurate oil tank gauge.
This article series describes how to find, read, and test the oil gauge on a home heating oil tank. If your oil tank is above ground indoors or outside it should have a fuel level gauge installed similar to the one shown in our photo.
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A heating oil tank gauge does a fine job of telling you the oil level in the oil storage tank: oil is near the top, 3/4 full, 1/2 full, or just 1/4 full or nearly empty. Sketch at left showing the location oil tank gauge and of places to watch for oil tank leaks is courtesy of Carson Dunlop Associates.
[Click to enlarge any image]
"Full" in this case just means the level of oil in the tank, not an accurate read of the number of gallons of heating oil remaining.
Oil tank gauges are not accurate in reading the quantity of oil in a tank in gallons or liters. But then neither is the gas gauge in your car - and for the same reason. The tank shape.
What's inaccurate about all oil tank gauges is that because most oil tanks are not square but round or oval, knowing the height of oil in the tank does not tell us very accurately just how much oil is in the tank except at three points:
Scully produces the "Golden Gallon Gauge" that can provide an accurate readout of the level of oil in indoor our outdoor oil storage tanks, including buried oil tanks.
Scully gauges are a double float that communicates to an oil tank level gauge that can be read in inches, gallons, imperial gallons, or liters.
The Scully oil tank float gauge fits oil tank tapped openings of 1 1/2" or 2" diameter (NPT), and can handle oil tanks up to 60" in tank depth (from gauge mount to tank bottom).
Scully's product literature indicates that this is the most accurate oil tank gauge of its type.
Contact the Scully Signal Company.
When we bought our house, our (oval 275 gal) tank had a reading of about 7/8 (halfway between F and 3/4) and our oil company estimated this to be 190 gals, which would be closer to 2/3 than 7/8 and certainly below 3/4, which it was not. We used this oil from the time we bought it, through the end of last year's heating season until the end of this September.
At this point, we had about 1/8 of a tank. We received a fill-up, which was for 203 gallons and put us at full. It would reason that with an oval tank, the round parts at the top and bottom (round parts) would hold less oil per vertical inch than the middle (straight parts).
That being said, it seems like the top 1/8 and bottom 1/8 combined hold about 150 gallons, or half a tank's worth. Other than this, our oil gauge seems to be reading fine, in that it went from full to half over the course of late September to today (middle of December). I just got a fill up and my tank was reading almost exactly at 1/2, but it was only 100 gallons to fill it.
Is this normal? Is the gauge reading relatively accurately? Does a 275 gallon tank actually hold 275 gallons? - RJ
I have 2 275 gallon oil tanks. I had 150 gallons of oil delivered when the gauge showed I had just less than an 1/8th of oil in the tank. After the 150 gallons was put in the gauge went just above 1/8th. How is that possible? 150 gallons represents 1/4th of the tank and the tank already had oil in it? - Carl 6/20/2012
(Oct 2, 2014) jen said:
I have two 275 connected tanks with one gauge. My gauge read 3/8 so I ordered 275 gallons. The driver was only able to fill to 183 gallons and told me my tanks were full. I understand that although my tanks read 275 gallons, it is actually 260 which goes into each of them. Since the reading was at 3/8, I should have easily been able to hold the 275 (137.5 in each). I believe I may have a blockage but my oil company does not feel as such. Thoughts??
RJ, there are a few sources of confusion about just how much oil a particular oil tank holds, how much is in it at any given moment, and about just how near to capacity the oil company fills the oil storage tank during delivery.
Maybe so, Carl. Consider that especially when filling the lower section (or top section) of an ovate oil tank, the gauge, which moves linearly, can't accurately reflect the actual tank amount. The gauge is accurate only at 3 points: empty, half empty, and full.
When filling two 275g oil tanks simultaneously, you got 75 gallons into each tank. If the tanks were actually nearly empty, you've filled 1/4 of one 275-g oil tank (75/275 = 0.27) but since there are 2 tanks, you've got to divide that again by 2, so you've filled just about 1/8 of each tank - which is what the oil gauge is reflecting.
In this photo of an oil tank gauge (above) the red disk is sitting above 3/4 - showing that the heating oil level in this oil tank is more than 3/4 full. For readers who have asked "Do I read the oil level at the top, center, or bottom of the red disc?"
I have to say that the gauge is nowhere near accurate enough to be read with that precision, particularly with round or oval oil storage tanks. Unless your oil tank gauge has been calibrated with care and is measuring oil in a rectangular oil tank, the gauge is only close to accurate at empty, half-full, and completely full levels.
The following photo is from your site and is just like mine. It has a disc in a tube like the one below and red marks on tube as shown. The disc is like a checker. And I was wondering if you read the top edge or bottom of checker. - Cliff by email 12/5/2012
Now that you sent us our own photo and an email query I understand the question better.
I apologize that my answer may not be very satisfying, but to be safest, I would read from the bottom of the plastic disc. That's because the object is to avoid running out of oil and suffering the consequences of lost heat. In general I call the oil company immediately if the tank shows 1/4 full or less.
On a 250g oil storage tank on most residential heating installations in typically cold winter weather I figure if the oil company cannot make an oil delivery a day or two we're still safe.
Having taken a few of these gauges apart I can assure you that they are certainly not precise. Not only is there play (or even bends) in the float mechanism that drives the oil tank gauge, but worse, because the oil storage tank is typically ovate in cross section, the ONLY chances that the gauge even MIGHT be precisely accurate are in three positions: Full, half-full, and Empty.
Watch out: as we get near the bottom of the oil tank, because of that ovate shape, the oil level falls more rapidly than while we're using oil from a tank filled around mid-way.
Watch out: for oil storage tanks whose fuel lines are taken off of the top of the oil tank, the installer almost never places the oil pick-up line all the way at the bottom of the tank. Typically the line is kept a several inches or even more above the tank bottom in order to avoid picking up sludge or water that might be sent to (and foul) the oil burner.
For this reason, we never use the very last bit of oil in the storage tank. This means that for practical purposes (actually being able to draw oil from the tank) that last 1/4 or 1/8 of an oil tank level showing on the oil tank gauge may in fact be very close to TANK EMPTY.
Does the gauge in the attached photo read 1/4 tank or 5/16? I guess the main question is, "Do I read from the top of the marker or the bottom?" - T.G. 1/6/2014
[Click to enlarge any image]
Generally we read the center of the plastic disc against the scale. I know this sounds like begging the question, but oil gauges are just not that precise.
Watch out. You are risking a more fundamental error. The oil tank gauge is not accurate anywhere near the range of precision of your question unless your oil tank is a cube or rectangle rather than the oval cross section most often installed.
Search InspectAPedia for Oil tank gauge accuracy for details and for the math used to calculate oil tank volume for oval tanks.
At 1/4 tank remaining and especially if the oil lines exit at the top of the tank (meaning the tank is never fully emptied anyway) its time to call for an oil delivery.
2018/01/21 Jamie Hall said:
I have just filled my tank two weeks ago. It’s now at less han 1/8 of a tank. I rarely keep it past 68 and off on warmer days. It takes over 300.00 and it’s only been two weeks!!! Coukd the gauge be broken?
2018/01/27 (Mod) said:
First let's check for a stuck oil tank gauge - some gauges have a removable plastic cover that lets you press the level indicator down or pull it gently up to assure it's not jammed. Of course the time to check the gauge would be right after the tank has been filled.
Oil delivery temperature will not explain ANY significant differences in the oil tank fuel level.
2018/01/25 Long Island said:
Perhaps you oil company is cheating you. If they deliver the oil warm it seems full on the gauge but will drop the level when it cools. A lot of oil company’s don’t provide the correct oil they say they give. One way for the oil company to offer cheap pricing. They simply don’t give you all the oil.
Continue reading at OIL TANK GAUGES - home, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see GAUGES ON HEATING EQUIPMENT
Or see HEATING OIL USAGE RATE to compare oil tank gauge readings with oil consumption rates.
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The plastic cover that covers (shows the 1/8 markings) the gauge of my oil tank broke/cracked.
Do you know where I can get a replacement? - Robert Muller
I have got a Worcester Camray 5 which is located in the garden. I had an indoor plug in oil level indicator but it has gone missing - where can I get a replacement one please. - Karen Gallant 6/27/12
The plastic part that covers your oil tank gauge is called the gauge vial. You can get one from a local oil heating equipment parts supplier or online. At oil storage tank gauge vials [above in this article] we have added photos and details. - Reader G.C. [Thanks GC] .
Karen the Worcester Camray 5 is a discontinued oil fired heating boiler. I don't know about the oil level indicator you cite - but if it is a device mounted on your oil piping or oil tank, I would imagine your oil heat service company can install a generic replacement.
Question on a fuel oil tank gauge: 275 gallon outside, vertical, 8 years old, in good repair. Sees Maryland winters.
Last spring, my oil supplier left a note that the standard float gauge did not work. In summer, I removed and cleaned the plastic dial cover with Mineral Spirits and a bottle brush
It was heavily coated inside, almost opaque, a bright red hardened gum. Then gently pushed the float down into a full tank, cycled this slowly several times full range, and it worked for almost a season. Now with the last fill up, it again is stuck on empty. Is there a gum in No 2 FO? Does it splash up and glue the float mechanism? How often does the gauge need maintenance? Mr. R.L. Hails Sr. P.E. 2/25/2012
Oil tank gauges often work reliably for decades and do not require maintenance. On occasion if a gauge stops working it's possible to free up stuck parts by simply moving the gauge operating parts a bit. If that doesn't work, replace the gauge.
I have a float gage (319 gallon indoor oval tank), the tank went empty and was filled with 200 gallons however the gage did not return to show approximately 3/4 full. Is it because there is liquid sitting on top of the float gage? If so, is there a way to correct this so the tank reads accurately? - Ian 8/7/12
The float arm may be bent or the gauge sticking. You should be able to carefully disassemble, remove from tank, un-bend, un-stick moving parts (or replace them).
If your oil tank gauge looks like the one at the top of this page, try first unscrewing the plastic cover and press down gently on the gauge top indicator - the whole assembly will move and you're pushing the tank float and arm up and down inside the tank - sometimes this will free up the assembly without further ado.
Oil won't be delivered unless the tank gives out a whistle, please explain since I'm new at this. and what can I do. Thanks. - Felix S 11/12/12
The oil tank whistle is a device at the top of the oil tank that emits a sound that lets the oil delivery truck driver know when the tank is full. It has nothing to do with the transfer of oil from the oil tank to the heating oil burner.
(Dec 20, 2012) Joe said:
I recently bought a forclosed home that was built in 1957 with oil heat. The house is a 1700 sq feet brick ranck home. The oil was at 5/8 full when I moved in. I have been working on it for 4 hours a day at 60 degrees. I turn it down to 50 degrees when I leave. In one week I checked the gage and it was at 3/8s of a tank. I cant imagine it sucking that much oil. It is really bothering me how unbelievable ineffecient it is. Does anyone have any advise?
(Jan 1, 2013) Darlene said:
I had 1/2 oil in my tank,I then got 100gal and the gauge stayed at 1/2,so I went and got a new gauge and it seems to stay at 3/4. It does not more?
(Jan 1, 2013) Karen said:
Our oil tank has just gone a sliver below the 1/4 mark. Our landlord has always told us never to let this happen. Due to the holidays and financial difficulty, we cannot get oil for 3-4 days from today(12/31). Is something terrible going to happen? Im very worried. This is the first time in 10 years this has ever happened. Any thoughts?
(Jan 4, 2013) todd said:
joe, your furnace is working harder to get to 60 from 50 than say from 56 to 60 ,leave it a higher setting than 50 or try smaller lncrements
(Jan 4, 2013) todd said:
Darlene… as stated above gauges are not 100% correct 3/4 is the safe fill level,in 10 years as a oil truck driver a gauge that reads 1/2 will take only 100 gallons, your tank is at max capacity
(Jan 4, 2013) todd said:
Karen you can put 5 to 10 gallons of diesel fuel to last 1 or 2 days (20 to 40 dollars)
(Jan 4, 2013) Stan said:
My oil tank was half full and yesterday I had it filled to the max. This morning the gauge reads empty?
(Jan 4, 2013) todd said:
Stan check for leaks then check for sticking gauge
(Feb 26, 2013) Robin A said:
I have a 275 G tank without a TLI. The 1.5" vent line has a capped end that I stick a stick in to see what the level of oil is. The top of the capped nipple is about 10" above the top of the tank. Can I just stick a TLI in this hole? I have found a couple examples that I think will work such as the Krueger Sentry Galvanized Direct Reading Gauge. It indicates it has a "tank depth" of 6" and I'm not sure what that means. I also found a similar gauge that has a "tank depth" of 10" - not sure what that means either. Can you help? Thanks!
Most likely the oil tank fuel level gauges you describe, when they refer to a "tank depth of 10" " are saying that the gauge can measure oil level in a tank at depths anywhere *between* 10" and a deeper level, typicalliy 144".
You need room above the tank to insert the new gauge and you'll be all set.
There are various LED and other electronic oil tank fuel level gauges that permit remote reading of the level of oil in the tank, but all of them require some sort of sensor or float inside the tank where the oil level will be monitored.
Krueger, the company you mentioned, provides an "LED at a Glance" LED Clamp-on device that will convert the position of the float gauge indicator into an electronic signal of oil level that can then be read by a remote display - that feature may not be one you need.
Contact Krueger directly at
Krueger Sentry Gauge
1873 Siesta Lane
Green Bay, WI 54313
Telephone: USA 1-920-434-8860
(Sept 9, 2014) Rob R said:
the gauge vial on my tank is broken/missing. The sending unit is working perfectly so I am able to guestimate the gallons of fuel in my tank. I have searched for a replacement vial online but they all are threaded vials. Mu issue is that my gauge is held onto my tank with four small screws. You have a photo of the type that I have as the first picture under your " How do we know that the oil tank gauge is working?" paragraph. There are no threads on the gauge mounting hole. Can you provide any insight on how to replace this type of gauge or vial?
It may be most simple to replace the entire oil tank gauge assembly rather than waste a lot of time looking for an obsolete part. Krueger, mentioned below sells a variety of oil tank float gauges and tank bushings that will probably work fine for you.
Or use our email found at our CONTACT link and send me some sharp photos of your gauge and I'll see what I can find for it.
J. Ross Keys said:
If a supplier overfills a oil tank in the basement of a dwelling and the fill pipe is full, is it possible that the hydraulic head of the liquid above the gauge would leak oil? In other words if a plastic level gauge is installed correctly, what pressure rating are they designed to hold under manufacturing testing?
Definitely. Oil tank gauges, depending on the type and design, can leak if an oil storage tank is overfilled. I think that the leakage will be more severe during fill-up as the tank is being filled under pressure, applying greater oil pressure to the gauge and its seals than just that from the head of oil remaining in a fill pipe afterwards. Examples are in the article above.
(Oct 10, 2014) Anonymous said:
What kind of valve to use to prevent air bubbles in the fuel line
(Nov 26, 2014) Anonymous said:
we have two 275 gallon oil tanks. the furnace was not coming on, technician blew out the line, and after a while, some oil came in.
However, he said that the crossover line between the two tanks must be getting clogged, as the oil is not flowing freely from one tank to the other. He measured the front one, said it had 18 inches, the back one seems to be full or close to full. The way the tanks were installed it is almost impossible to reach the valves on the bottom of the back tank, the crossover line etc. He says they need to empty the tank, and turn them to both face front, so that a person could get to all the valves etc. Is this really the only way to go?
Good grief what a lot of trouble, and what a thoughtless original installation. Unfortunately when blowing out an oil line cannot adequately clear it, replacing the line is a typical solution, along with use of an oil additive to break up sludge, along with sludge removal from the tanks along with increased filtration at the oil burner to avoid clogging by the sludge released by the whole procedure.
It's just about impossible to install a new balancing line between the two tanks connected to tank bottoms without first emptying the tanks. If going to that much trouble (emptying tanks) I'd look at sludge removal at the same time, or even tank replacement if the tanks are quite old and rusted thin since much of the cost is in the labor.
An alternative MIGHT be to close off the clogged lines and install new, larger diameter oil lines coming off of the tank tops. But some clever piping may be needed to assure that both oil tanks are used when tapped from the top
(Jan 3, 2015) Anonymous said:
One solution that worked for me is to install an oil filter housing without filter in line before your oil filter. This is the lowest point and will gather all the sludge and water. This way the sludge comes to you. The only cost is the housing and a gasket. Techs refer to this method as a sludge pot. Hope this helps.
(Jan 28, 2015) Anonymous said:
oil tank vent alarm not working, what could be the cause?
Tank is not filled to the vent
The alarm is clogged or has lost a part
Insect clogging in the vent pipe
(Feb 13, 2015) Anonymous said:
I asked the oil man to fill my tank that read 1/8 tank. When he came he pumped 110 gal and it indicated full to delivery man. The guage read 1/2. They told me that foam formed when new oil was put into tank that caused it to indicate full and stop pumping. I've never heard of such a thing! Any comment?
What you describe is not something I've come across but it has been described as an effect that can occur if there is water contamination in the oil storage tank; during delivery the incoming oil, delivered fast and under pressure, can stir up water and form foam - this can also clog up the heating oil piping, filter, burner, and lead to loss of heat.
I'd ask the oil company to check oil tank water level, remove excess water, and go from there.
I'd also check - if you can - about just what was being delivered to you - if your oil tank didn't have much water in it before then water could have come in a bad delivery. I've seen this happen if the oil truck is filled from a depot tank that is low on oil, has water in that tank bottom (which is normal) and is itself stirred by a depot delivery while the oil truck is filling.
Experts have written about this
(Mar 2, 2015) Anonymous said:
what are the correct positon of the two ball
levers on top of outside oil tank
Sorry Anon you'll have to use our contact link found at page bottom to send me photos - I 've no idea what you're asking about;
Send me some sharp photos and we can comment more usefully.
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