Replacing an oil tank gauge
A float gauge is a cheap part that fails in boring ways: the float sticks, the vial fogs over, the disc drops off and reads empty forever. Swapping a plain one is a small job. Two things decide whether it stays a small job, and both are settled before anyone picks up a wrench: whether the gauge matches your tank's depth, and whether you have a plain gauge at all or a combination unit built into the vent line.
First, make sure it is actually the gauge
A gauge that has not moved in weeks of heating is not a lucky tank, it is a stuck float. But a gauge reading oddly is not always broken, so spend two minutes before you spend money: take a stick reading and convert it on the chart for your tank. If the stick and the gauge disagree, believe the stick. The four ways these gauges lie, and how each one looks, are in reading an oil tank gauge.
Worth knowing before you order a part: sometimes only the clear vial is cloudy or cracked and the mechanism underneath is fine. Vials are sold on their own for exactly that reason, and they are the usual casualty on an outdoor tank, where the plastic breaks down in the weather until you cannot read the disc through it. A vial costs less than the whole assembly and is a much smaller job, because nothing comes out of the tank.
A combination gauge and vent alarm is a different job entirely
On plenty of tanks the gauge and the vent alarm are one combination unit, and that single detail decides whether you are looking at a twenty minute swap or an afternoon of pipe work. Establish which you have before you order anything.
The other half of the rule matters just as much: a combination unit is replaced with another combination unit. Put a plain gauge in that spot and the tank has lost its vent alarm, the whistle that tells the driver when to stop. A careful driver who hears nothing will refuse to fill the tank. An unlucky one will not, and that is how tanks get overfilled.
Match the gauge to your tank's depth
This is the part people get wrong when ordering online. A float gauge is built for a particular tank depth, because the arm has to reach the bottom of the tank and swing through the whole range. A gauge sized for an upright tank in a tank lying on its side will not read correctly, and may not physically work at all.
The number you need is your tank's stick depth, which is the same number the charts on this site are built around:
| Tank | Depth the gauge must cover | Chart |
|---|---|---|
| 275 gallon vertical | 44″ | 275 gallon vertical oil tank chart |
| 275 gallon horizontal | 27″ | 275 gallon horizontal oil tank chart |
| 330 gallon vertical | 44″ | 330 gallon vertical oil tank chart |
| 330 gallon horizontal | 27″ | 330 gallon horizontal oil tank chart |
Depth is the vertical distance the oil occupies, which is what both the stick and the float arm travel. The standard upright 275 and 330 are 44 inches deep; the same tanks laid flat are 27. Listings for the common vertical gauges are usually written as written for tanks 42 to 44 inches deep.
The second number is the thread. These gauges are sold in 1.5 inch and 2 inch male NPT, and the tapping on your tank decides which one you need. Pull the old gauge or look at what is written on it before ordering, rather than guessing from a photo.
Which gauge for which tank
| Tank | Depth | Gauge |
|---|---|---|
| Upright 275 or 330 (steel oval) | 44″ | Beckett 14504 King gauge, built for 42 to 44 inches, with both a 1.5 and a 2 inch thread (Beckett vertical gauge on Amazon) |
| 275 or 330 lying on its side | 27″ | Beckett horizontal gauge (OEM 4503). The 42 to 44 inch vertical part is the wrong gauge here (Beckett horizontal gauge on Amazon) |
| Roth 400L / DWT400L (110 gallon) | sealed tank | Roth sealed fuel oil tank gauge, part 2335003411 |
| Roth 620L and 1000L / 1000LH (165 and 275 gallon) | sealed tank | Roth sealed fuel oil tank gauge, part 2335001863 |
| Roth 1500L / DWT1500L (400 gallon) | sealed tank | Roth sealed fuel oil tank gauge, part 2335000191 |
For the common steel oval the choice really is just upright or on its side, and the depth decides it. Roth tanks are their own world: their gauges are sealed-tank parts with Roth part numbers and are not interchangeable with the steel-tank gauges above.
The Amazon links above are affiliate links: this site may earn a commission at no extra cost to you, and it does not change which gauge is right for your tank. Roth gauges are ordered by part number through a Roth dealer or a supply house rather than from Amazon.
What the job actually involves
This is the plain gauge, threaded into its own tapping, and not the combination unit above. The work itself is short. The care is all in the details, and every one of them is a way to turn a twenty minute job into a weeping tapping or a ruined new part.
- The tank is full of oil vapor. Pulling a gauge means opening a tapping on a tank holding fuel. No flame, no smoking, and ventilate the space.
- Run the float the long way down the tank. The arm wants to swing along the tank's long axis where it has room, clear of the ends. Keep it away from the fill in particular: oil coming in on a delivery lands hard enough to twist or break a float sitting underneath it. A float that fouls on anything reads wrong from day one.
- Hand-start the threads. Cross-threading a gauge into a tank tapping is easy and unforgiving. It should turn freely by hand before any wrench touches it.
- Use a pipe dope rated for oil. Pro Dope and Gasoila are the usual choices, and any oil-rated dope does the job. The wrong sealant weeps, and a weeping tapping on top of an oil tank is a slow mess that is far harder to fix than it was to prevent. This is the steel-tank rule: a Roth sealed gauge seals on an O-ring instead and takes no dope or tape at all.
- Do not overtighten. Many of these bodies are plastic.
Getting the float in without wrecking it
This is the step that ruins new gauges, and it is the one worth reading twice. The float has to go into the tank held all the way up. Let it hang down while you turn the gauge in and it catches the side of the tank and twists, and what comes out of that is either a broken gauge or one that never reads properly again. A gauge damaged this way is damaged on the way in, before it has measured anything.
The clean way is two-handed: take the vial off the top of the gauge, hold the level indicator up with one hand, and work the pipe wrench with the other. That keeps the arm raised through the whole turn.
There are field workarounds for when you cannot manage both at once. Some people wedge a piece of cardboard against the indicator to hold it up. Others put a rubber band on the arm to keep it raised and let the oil break the band down on its own once the gauge is seated. Neither is as good as simply holding it, but both beat letting the float swing free while you turn.
Common questions
How do I know what size gauge to buy?
Two numbers: your tank's depth and the thread. An upright 275 or 330 is 44 inches deep, and the same tank lying flat is 27, so the two take different gauges. The thread is 1.5 inch or 2 inch male NPT depending on the tapping. Check the old gauge before ordering, and use the depth table above to confirm which tank you actually have.
My gauge and my vent alarm look like one part. Can I still replace it?
It can be replaced, but it is not the same job and it is not a straight unscrew. A combination unit is built into the vent line, so getting at it means dismantling the vent pipe from the outside in and putting the run back together afterwards. It also has to be replaced with another combination unit, because a plain gauge in that position leaves the tank with no vent alarm and no overfill protection during a delivery. This is the swap to hand to your oil company.
Can I replace the gauge with oil in the tank?
It is done that way routinely, since the gauge sits above the oil. The thing that matters is not the oil level, it is the float: it has to be held all the way up as the gauge goes in, whatever is in the tank. Let it hang and it catches the side of the tank and twists, which breaks the gauge or leaves it reading wrong forever. Take the vial off and hold the indicator up with one hand while you turn the wrench with the other.
Only the clear vial is cloudy. Do I need the whole gauge?
Usually not. Vials are sold separately, and on an outdoor tank they are the part that goes first: the plastic breaks down in the weather until you cannot read the disc through it. A new vial costs less than the whole assembly and does not involve opening a tapping at all, so check what your gauge takes before buying the full unit.
Is a gauge worth replacing at all, or should I go electronic?
A float gauge is the cheap, no-power, nothing-to-configure option and it is what most tanks have. If what you actually want is the level on your phone, that is a different product with its own limits and requirements, covered in WiFi and smart oil tank gauges.
Related
- Reading an oil tank gauge (and the four ways it lies)
- The oil tank whistle (vent alarm)
- WiFi and smart oil tank gauges
- How to stick an oil tank
- All tank charts
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