An oil tank holds a supply of fuel oil for a boiler, furnace or water heater. Most above-ground oil tanks have a tank level gauge on top, while many buried tanks have an outdoor level indicator near the building. A homemade manual gauge is implemented to check the oil level in a tank that does not have a level indicator. Oil company customers monitor the tank level to keep track of the oil supply and know when to call for fuel delivery. Check the oil level in your tank regularly to ensure a constant supply of fuel.
Locate the tank level indicator. The tank level gauge is a clear plastic tube with typical tank measurements to mark the oil level at "Full, 3/4, 1/2, 1/4 and Empty." Look on top of an above-ground oil tank. Search the grounds near any buried oil tanks.
Read the tank level displayed by the gauge. A red or black level indicator will cross the level marks on the gauge. Discern the approximate oil level based on the location of the indicator, where an indicator level between the 1/2 and 1/4 marks shows approximately 3/8 of a tank.
Estimate the fuel level in a tank that does not have a gauge. Open the top valve cap by twisting it counterclockwise. Insert a 5- to 6-foot straight stick, or a cord with a weight at the end, and drop it straight down until it stops against the tank bottom. Mark the stick or string at the tank top and remove it from the tank. Look at the wet level of the string or stick and the mark showing the tank top. Estimate the oil level in the tank by differentiating between the length of the tank top mark and the length wet by oil. If the oil mark covers half the stick, or string, the tank is about half full.
Request a measuring stick from your oil company. Measuring sticks were commonly used before floating gauges were implemented. Many oil companies deliver fuel regularly without customer requests. The company may consider average use, or meter the tank level with electronic remote sensors. Ask your oil supplier if fuel deliveries are made regularly, or on request.