Replacing an oil tank gauge

First, make sure it is actually the gauge

If the gauge has not moved in weeks of heating, the float is stuck. But a gauge reading oddly is not always broken, so spend two minutes on it before you order a part: 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.

Sometimes only the clear vial is cloudy or cracked and the mechanism underneath is fine. Vials are sold on their own for 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.

Everything below is about a float gauge on a steel tank. A sealed Roth, a wall-mounted pneumatic gauge and an ultrasonic monitor each take their own part, and which gauge fits which tank sorts those out by the tank rather than by the feature list.

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. A plain gauge is a twenty minute swap; a combination unit is an afternoon of pipe work. Establish which you have before you order anything.

A combination unit also has to be 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 no whistle will stop and refuse to fill the tank. One who fills it anyway can overfill it.

Match the gauge to your tank's depth

This is the part that goes 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:

Part numbers, depth ranges and thread sizes here are taken from the manufacturers' published listings and supply-house catalogues, not from hands-on testing. Catalogue numbers vary between sellers for the same part, so check the depth and the thread against your own tank before ordering.

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

The Amazon links above are affiliate links: as an Amazon Associate this site earns from qualifying purchases, 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. Getting any of the details below wrong turns 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 to clean up. 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. 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 you end up with either a broken gauge or one that never reads properly again.

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.

If you cannot manage both at once, there are field workarounds. 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.

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