Oil Level Indicators

The Oil Level Indicator (OLI) was developed in response to the need of maintenance professionals to gauge the oil level inside large tanks, gearboxes and reservoirs. The OLI is a clear acrylic column with 1/2" NPT threads at each end. Red and green level marker stickers are included with the OLI to mark upper and lower limits, or to designate running oil level and idle oil level. Utilizing the drain port, operators can visually monitor the fluid level within reservoirs.

* Stainless steel fittings and breather cap sold separately.

Explore the oil level indicator


  • Stain-resistant acrylic

Recommended Temperature Range

  • -40˚F to 200˚F
  • -40˚C to 93˚C

Maximum Operating Pressure

  • 65 psi
  • 4.48 bar

Chemical Compatibility

  • All mineral and synthetic oils

Available Options

  • Lengths ranging from 3" to 15"
  • Stainless steel fittings
  • 2 micron breather cap (3" to 12" models)
  • Custom lengths available upon request
Part Number Description Overall Length Diameter of Acrylic
DC-OLI3 3" OLI - 1/2" MNPT X 1/2" MNPT 3 in / 7.62 cm 0.875 in / 2.223 cm
DC-OLI6 6" OLI - 1/2" MNPT X 1/2" MNPT 6 in / 15.24 cm 0.875 in / 2.223 cm
DC-OLI9 9" OLI - 1/2" MNPT X 1/2" MNPT 9 in / 22.86 cm 0.875 in / 2.223 cm
DC-OLI12 12" OLI - 1/2" MNPT X 1/2" MNPT 12 in / 30.48 cm 0.875 in / 2.223 cm
DC-OLI15 15" OLI - 1/2" MNPT X 1/2" MNPT 15 in / 38.10 cm 0.875 in / 2.223 cm



  • Pumps
  • Gearboxes
  • Storage Tanks

Why use an Oil Level Indicator instead of a vented sight gauge?

The old style vented sight towers are made of regular glass that is prone to breaking. The brass housing provides some protection, but creates the problem of low-to-no visibility of the oil color, quality and level. The OLI is made of strong cast acrylic that provides 360° of oil level viewing.

Which size Oil Level Indicator do I need?

Measure the distance from the drain port of your equipment to the top of the oil level. Once you determine this measurement, select the next longest available size of the OLI. It is recommended that you choose an OLI at least 1" taller than your actual oil level to avoid spilling caused by over-filling or underestimating the level of oil in your equipment.

I’m concerned about the Oil Level Indicator breaking. What can I do to prevent this? 

Install the OLI in a location that is protected from mobile equipment or other high-impact hazards. It is also recommended that users install a ball-valve between the drain port and the product being used. The ball-valve allows instantaneous shut-off of oil flow if necessary.

How is the Oil Level Indicator installed?

Use an elbow to install the OLI at the drain port. It can be installed with the optional breather at the top 1/2" NPT port. If you require a closed loop, the 1/2" NPT can be used as a connector port to feed back into the system. For units longer than 12", it is recommended that users install a support bracket for stability.

How can I clean/replace the Oil Level Indicator without having to drain the oil from my equipment?

Installing a ball-valve between your drain port and the OLI will allow users to shut-off the flow of oil in order to clean or replace the product.  Cleaning the products typically requires just soap and water. Cleaning agents should be avoided, as they can cause fogging, crazing and degradation of the optical quality of the acrylic. 

When should I replace my Oil Level Indicator?

The OLI will last for years, but different applications can shorten the life of the product.  Years of exposure to sunlight, extreme weather or caustic chemicals will degrade the acrylic over time. Watch for fogging, crazing (small cracks appearing on the surface of the acrylic) or oil weeping from bonded surfaces. These are signs that the product is in need of replacement. If installed outside and exposed to harsh conditions, the products should be replaced every 2-3 years. Indoor applications typically have a life-span of 3-5 years. It is highly recommended that you never use an OLI for more than 5 years without replacing it.