February 28, 2021

How Accurate is My Fuel Tank Gauge?

If you read our previous blog on reading your oil tank gauge, you already know how to properly read it and the signs to look for to in the event that it needs to be replaced. If you haven’t read the blog yet, you can access it here.

Since heating oil tanks have remained relatively unchanged for decades, so have the gauges inside of them. Unless you’ve installed a different type of gauge, the odds are that your home heating oil tank has a float gauge used to measure the amount of oil left inside.

How does a Float Gauge work?

A float gauge is a very simple mechanism that has a plastic site at the top with a disc that indicates the oil level in the tank which is attached to an articulating arm with a hinge in the middle. The other end of the arm is attached to a float. When the oil level lowers, the float lowers, and in turn, lowers the gauge in the site glass.

How accurate is my Float Gauge?

Float gauges are not a precise tool therefore they are not very accurate in their measurements. One main reason is that float gauges go bad over time. After years of sitting in heating oil, the float builds up sludge over time. This can actually cause the float gauge to get stuck. If the gauge rotates in the tank the arm can get stuck against the side of the oil tank and the level on the gauge site won’t change no matter what the oil level is.

Float gauges also don’t take the geometry of the tank into consideration. The float gauge’s job is to simply raise and lower with the level of oil in the tank, but it doesn’t consider the curvature of the tank. The middle of the oil tank has fairly straight walls, meaning there is much more oil in that part of the tank than at the top or bottom where the walls are more curved. You may have noticed that the oil level lowers faster at the top quarter of the tank and the bottom quarter of the tank. So, if you have less than a ¼ tank of oil, your usage is faster than it is when you go from ½ to ¼ due to the tank curvature.

Is there a way to get a better gauge of my oil usage?

The easiest way to prevent running out of heating oil is to sign up for automatic delivery with your heating oil provider. They will track your usage compared to the average daily temperature and figure out exactly when to schedule your oil deliveries, so you don’t have to worry about running out.

Another option is a Smart Oil Gauge. It uses an ultrasonic sensor to detect your oil level vs. a float. Using the geometry of the tank, it can determine how many gallons of oil are left in your tank vs. just an approximate level. It doesn’t come into contact with the oil, so it doesn’t build up sludge. You can also track additional data:

  • Current oil usage (gallons per hour and gallons per day)
  • Days until you will be at 1/4 tank
  • Days to 1/8 tank
  • Total gallons used (per day, week, month, or year)
  • How much home heating oil can be delivered to your oil tank

It’s a neat alternative to the traditional float, and most homeowners can install it themselves and track the data on a cell phone app.

Regardless of what oil tank level measuring tool you use, it’s important to understand how fast you use your home’s heating oil and make sure that you don’t run out.

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