Oil tank piping requirements sketch Guide to Oil Tank Gauges

  • OIL TANK GAUGES - CONTENTS: How to find, read & test the oil tank gauge - how much oil is in the heating oil storage tank? What are the different types of oil tank gauges and indicators of oil level?Types of oil tank gauges to measure how much oil is in the oil tank; Special gauges for buried oil tanks - underground tanks - tell how much oil is in the tank without having to use a dipstick; Heating oil tank gauge accuracy, inspection, installation, defects, repair guide;
  • POST a QUESTION or READ FAQs about oil tank gauges: buy, install, repair, replace, read, or troubleshoot residential and light commercial oil storage tank gauges

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How much oil is in the oil storage tank? Heating oil tank gauge installation, reading, testing, repair guide: how much oil is in the heating oil tank? How accurate is the oil tank gauge? This article describes how to find, read, and test the oil gauge on a home heating oil tank.

If your oil fired heating boiler, warm air furnace, or water heater has stopped working, one of the first things to check is whether or not you've run out of fuel. 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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How to Find, Read, and Test an Oil Tank Fuel Level Gauge

Heating oil tank gauge (C) Daniel FriedmanOil tank gauges are pretty simple to find, recognize, and read. If your heating oil tank is above ground outdoors or indoors, look on top of the tank for a device similar to the one in the photos shown on this page.

If the heating oil tank has been enclosed for cosmetic or other reasons, it may be necessary to make an access door that can be opened to give a view of the oil tank gauge.

If the heating oil tank is inaccessible above ground or buried, remote oil level gauges are available. Installing a remote-reading oil tank gauge permits reading of the oil tank level from an readout device inside the building.

[Click to enlarge any image]

Article Contents

How does an oil tank gauge work?

A float assembly inside the oil tank moves up and down along with the level of oil inside of the oil tank.

As the float assembly moves up or down it pushes a metal rod upwards (oil level in the tank is going up) or lets the metal rod fall down (oil level in the tank is dropping).

On top of the metal rod is an indicator, such as the red plastic disk in our photo at left.

The red plastic disk forms a line inside the oil tank gauge, showing the level of oil in the tank.

In this photo of an oil tank gauge the red disk is sitting above 3/4 - showing that the heating oil level in this oil tank is more than 3/4 full.

How do we know that the oil tank gauge is working?

Well it's easier than you might think. On most oil tank gauges, the plastic tube that covers the actual moving gauge parts is just screwed into the cast iron base that holds the gauge assembly. Once in a while when we've wondered if our oil tank was really empty, or when an owner has reported that the oil gauge seems to "stick" we've done this simple test.

Old oil tank gauge (C) Daniel FriedmanUnscrew the plastic cover by hand. Don't grab it with Vise Grips™ or you'll probably break the plastic. The gauge cover turns counter-clockwise to remove it.

If you did break the oil tank gauge cover it's not a catastrophe - the heating system will still work, but you should replace it before your next oil delivery because a broken or missing oil tank gauge cover could lead to a costly oil spill during an oil delivery.

Now that the cover over the oil tank gauge has been removed and set aside (where it won't roll under the oil tank and get lost), and presuming your tank gauge is not already sitting at the bottom of its range of travel (empty), just press the top of the gauge indicator rod downwards slowly and gently.

You will feel a little resistance because you're pushing a rod and float down into the heating oil inside tank. When you have pushed the indicator partly or all the way down, release it.

You should see the tank gauge rise back to about where it was before.

This tells you that the hinged mechanism and float are still in place and that they are moving without obstruction.

If the gauge is broken, lost, or damaged, the entire assembly can be replaced by your heating oil technician.

Remember that a heating oil tank gauge is not lab-grade equipment. It is not precise to the quart, probably not even to the gallon.

We have made a video of the procedure for testing an oil tank gauge and will post it here soon.

What else goes wrong with heating oil tank gauges?

  • Water leaks: On an outdoor oil tank the gauge may be damaged or simply not well sealed, permitting water to leak into the heating oil tank - a cause of oil tank leaks, rust, and more immediately, water in heating oil can lead to loss of heat. Our photo below shows an oil level gauge on an outdoor oil tank exposed to roof spillage.

Seeping oil leak at the filler pipe (C) Daniel Friedman

  • Oil tank leaks at pipe fittings: if the oil tank gauge cover is damaged heating oil may be forced out of the oil tank during the oil tank fill-up operation.

    During oil tank fill-up oil may also seep out of pipe fittings at the top of the oil tank. If oil tank leaks at these locations are severe the pipes need to be removed and the connection re-made with a top quality pipe sealing compound that is oil resistant.

    Our oil tank video posted at You Tube explains when, where, why, and how to stop an oil tank at this location.

    Other places to look for oil tank leaks are shown in our oil tank sketch below. OIL TANK LEAK ADVICE contains detailed advice about leaky oil tanks.

    If the oil tank leak at the top of an oil tank is minor seepage, you may want to avoid the trouble of disassembling and reassembling all of the pipe fittings. On the seeping oil tank fittings in our photograph, we left a rag tied around the leaky pipe. The leak was at the pipe fittings not the oil tank gauge.

    The amount of seepage was just an ounce or so during fill up - the rag stopped oil from running down the sides of the oil tank and stinking up the garage where the tank was located. Once a year the owner replaces the dirty rag with a clean one. Paint-on sealants or epoxy applied to a surface which has been thoroughly cleaned of oil residue might also work in this location if the leak is really a minor seep.

Plastic bottle stuck into top of heating oil tank used outdoors (C) D Friedman

  • Oil tank gauges may stop working: if the moving float arm parts become bent or simply disconnected inside the oil tank.

    If you cannot fish out the damaged parts for repair using a bent wire hook, your oil heating technician will probably leave the old gauge parts in the bottom of your oil tank and install a new gauge, hoping the new gauge float won't foul and jam up in the old parts on the tank bottom.

  • Lost or broken oil tank gauge vial: the plastic vial that provides the oil tank level markings against which the oil tank gauge float indicator is read can be broken or lost.

    Our home-repaired oil tank gauge photo [left] shows a homeowner attempt at replacing a missing oil tank gauge vial. We worry that the plastic bottle stuck into the oil tank top around the float gauge indicator is fragile, leaky, and risks water contamination in the oil tank.

Typically the oil tank gauge vial is a screw-in part obtainable from your oil heat service dealer or from online oil tank gauge parts suppliers. - thanks to reader GC for this comment. <

Missing oil filler caps (C) Daniel Friedman

Here is a gauge on an outdoor oil tank. The red button resting at the bottom of the plastic tube to left of the galvanized tank vent pipe shows that this oil tank is probably empty.

This is a poorly installed oil tank, exposed to roof runoff, freezing temperatures, improperly closed vent opening, and more.

Check to assure that the oil tank gauge is present, and that its protective cover is tight. Loose or broken oil tank gauges can cause spills during tank fill operations.






How to Find Out How Much Oil is in a Buried Oil Tank or an Above Ground Oil Storage Tank that is Missing its Gauge?

Probing a buried oil tank (C) Daniel FriedmanYour oil company can provide a stick, a folding rule, or even a string and weight that can be placed into an oil tank to locate the bottom of the tank and to determine the level of oil in the tank.

The depth of the oil in the tank is measured by marking the top of the tank on the stick or oil tank gauge, then placing the stick into the oil tank and withdrawing it. The oil level seen on the stick is compared with the distance from bottom of the stick (bottom of the oil tank) to top of the oil tank (which we marked on the stick).

In the old days people kept an oil tank stick that was already marked and calibrated to tell them how much oil was in their tank. Today if we use a folding measuring rule or a generic "stick" to "stick the oil tank" to check oil level, we need to know the volume and shape of the tank as well as the depth of oil on the stick in order to calculate the number of gallons in the oil tank accurately.

In the photo our client is discovering a surprise buried oil tank at a farm we were inspecting.


Antique gauge for buried oil tanks (C) Daniel Friedman

Some buried oil tank systems use an oil tank gauge that measures oil in the tank and gives a reading at a remote location such as indoors near the heating boiler - which is pretty convenient in nasty weather.

Our photo shows an antique gauge used with a buried oil tank. Modern remote oil tank gauges include sensors which provide an LED or an electronic indication of the level of oil in the buried or remote oil tank.

But roughly, the oil tank stick procedure can tell us if the tank is half full, 3/4 full, or nearly empty.





How accurate are oil tank gauges

Conventional float type oil storage tank gauges are not precise in reporting the quantity of oil remaining in the tank.

Oil tank parts schematic showing the gauge (C) Carson Dunlop AssociatesA 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.

"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:

  1. When oil is at the top of the tank we know the tank is full. If we know (or calculate) the tank size or volume we know how much oil we have. Usually the oil company already knows your oil tank size - just ask them.
  2. When heating oil is at the bottom of the tank we know we don't have a bit - accurate but troublesome.

    Watch out: even on an oil tank whose delivery piping is connected to the tank bottom, it is not normal and it's not a good idea to run all of the oil out of an oil storage tank; there are risks of drawing water or sludge into the heating equipment, causing malfunction.

    Furthermore, when oil delivery piping is taken out of the top of the oil tank, the pick-up end of that tubing is never extended all the way to the tank bottom, exactly to reduce the chances of picking up water or sludge.
  3. When heating oil is exactly in the middle of a square, round, or oval shaped oil tank we indeed have an accurate measurement at this point.

Accurate Oil Tank Float Gauges

Scully oil tank gaugeBelow we offer an example of a high-precision float gauge used for oil tanks.

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.

Reader Question: accuracy of oil tank gauges

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.

  • Often the oil tank delivery driver fills an oil tank until the tank whistle indicates that oil is really at the top of the oil storage tank. But not always. Depending on the oil tank age and type, as well as the condition of the tank whistle or alarm (audible or not), the heating oil delivery driver may stop filling the tank before it is completely to the tank top. When this happens, trying to relate the size of the oil delivery in gallons to the tank size can be a little confusing. In other words, "Full" on the gauge, or "full" when the delivery person stopped pumping oil in the tank may not be a completely full tank.
  • Because oil tanks are often oval or round in cross section, a conventional float type oil tank gauge is accurate only when the level of oil in the storage tank is exactly at the mid point. Given the radius of the tank top and bottom curve, it is of course possible to calculate tank contents more accurately, but that's beyond what's needed for most situations.
  • Oil tank gauges on residential oil tanks are not precisely accurate. Please take a look at "How accurate are oil tank gauges" (above in this article) for details.
  • Oil tank sizes used indoors (and sometimes outside) at residential properties are often referred to generically as a "275 gallon tank" but actual oil tank sizes vary. Some typical capacities include 200 gallons, 225 gallons, 250 gallons, 275 gallons, and 300 gallons of oil. Take a look at the label that should be welded or glued onto your oil tank - the actual tank capacity may be indicated there.

    It's reasonable to ask your oil company what size tank they think you have installed. They might be correct.

    Otherwise if you want to get a pretty accurate estimate of the tank size [excluding the volume occupied by the thickness of the oil tank steel or plastic shell] you'll need to measure the tank height, width, length, and curve radius and do a spread sheet calculation. [Or ask our friend Paul Galow who has prepared an Excel spreadsheet that provides this function.]

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.

How to Read Oil Stroage Tank Gauges Accurately

Reader Question: how do I read the oil tank gauge against the scale: from the top, center, or bottom of the plastic disc?

Missing oil filler caps (C) Daniel FriedmanI have an oil gauge just like the one in the 5th image above. Has a checker like indicator. Do you read the bottom/middle/top edge of indicator as to the amount of oil in tank? - Cliff 11/13/2012

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.

Reader Question: how do I read the oil tank gauge?

Oil tank gauge showing oil level marker (C) InspectApedia TG 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.



Continue reading at HEATING OIL USAGE RATE or select a topic from the More Reading links shown below.


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