Petrometer gauges: how to read, pump, and fix them
If your oil gauge hangs on the basement wall with a little plunger on top and a red liquid column behind glass, you have a Petro-Meter style remote gauge. They are the standard way to read a tank you cannot see, especially buried tanks, and they are nearly all original equipment from decades ago, still working.
How it works
The gauge is a simple air pressure instrument with no electronics. Pressing the plunger on top (the aerator) pumps air down a quarter inch copper line to an air bell mounted about 2 inches above the bottom of the tank. The deeper the oil above that bell, the more pressure it takes to push air out of it, and that back pressure lifts the red indicating liquid up the sight column. The height of the red column reads in inches of oil on the scale, and inches convert to gallons with the chart for your tank.
Petro-Meter Corporation, the company behind the 1329 series, is a Long Island manufacturer (Lindenhurst, NY) and still sells parts for gauges installed generations ago.
This is one of five devices people call an oil tank gauge, and the only one that reads a tank you cannot reach. For how it compares with a float gauge, a Roth sealed gauge and an ultrasonic monitor, see oil tank gauge types.
How to read it
- Open the aerator if it is screwed down: turn counterclockwise until the plunger pops up.
- Pump in steady strokes. The red column climbs with each stroke and then stops rising. That stopping point is your reading. After service work on the line it can take around 25 strokes to purge the system; day to day it takes only a few.
- Read inches at the top of the red column. The gauge measures inches of oil, period. Convert to gallons with the chart for your tank size: 550 underground, fiberglass ball, 275 vertical, or any other on the charts page.
- A healthy gauge holds the reading. The column should sit at the level it reached, not bleed back down while you watch.
What each misbehavior means
| Symptom | What it means |
|---|---|
| Column keeps climbing past the known level with every pump | Blocked transmission line, air bell, or tank vent. The line needs to be blown clear with compressed air, a service-visit job. |
| Reading will not hold after pumping | An air leak somewhere between the gauge and the air bell, most often a union or the elbow fitting at the gauge that has worked loose over the years. |
| Reading bounces up and down within a few inches | A low spot in the tubing has trapped condensate or oil, and the air burps through it. The line needs blowing out, and ideally the trap rerouted. |
| Always off by the same number of inches | The air bell is not sitting at its standard 2 inches off the tank bottom, or the tank is pitched. The scale can be shifted to agree with a stick reading; after that, trust inches plus your chart, not the scale's printed gallons. |
| Plunger feels dead, no resistance | The aerator's internal seal is worn. The aerator is a replaceable screw-in part; the gauge does not need to be replaced for this. |
Causes per the Petro-Meter 1329 service bulletin, restated in plain language.
Maintenance, and where homeowners should stop
- Verify against a stick reading once a season where the tank allows it.
- Keep the aerator's small vent hole clear; a clogged vent keeps the column from dropping when it should.
- If the red liquid level is low or dirty, stop there. The indicating liquid (Red-X) is acetylene tetrabromide, a hazardous chemical: the manufacturer's own bulletin warns the vapor may be fatal if inhaled and that it corrodes drains. Topping off, cleaning, and refilling belong to your service company.
Common questions
Do I have to pump it every time I want a reading?
Yes, a few strokes. Pumping purges the line and pushes the column up to the live level; between readings the system slowly relaxes. The column should not collapse while you watch right after pumping, though. That points to an air leak.
The gallons printed on the scale do not match my deliveries.
The scale's gallon figures assume one specific tank under the gauge, and after decades of tank swaps they often disagree. Read the gauge in inches and convert with the chart for your actual tank. If the inches match a stick reading, the gauge is doing its job and the printed gallons are what is off.
My gauge is on the basement wall but the tank is buried outside. Is that normal?
That is the whole point of this gauge: the quarter inch tubing can run a long way, so the indicator lives somewhere convenient while the air bell sits in the buried tank. It is the standard setup for underground tanks alongside sticking the fill pipe.
Can I still get parts for a fifty year old gauge?
Usually yes. The design has barely changed, the aerator is a standard screw-in replacement part, and the manufacturer still operates on Long Island. A service tech can rebuild most of them in one visit.
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