How To Drain Water From Bobcat Doosan Tier 4 Fuel Filter

Maintaining the health and performance of your Bobcat Doosan Tier 4 engine starts with one of the simplest yet most essential tasks: draining water from your fuel filter’s water separator. Allowing water to accumulate in the fuel system can dramatically reduce engine efficiency and eventually damage expensive fuel system components. Fortunately, draining the water is quick, clean, and easy, and performing this small job weekly can save you from major repairs down the line.

In this guide, we break down how a Bobcat fuel filter works, why water collects in the separator, and how to correctly drain it to keep your machine running at peak performance.

Overview of How a Fuel Filter and Water Separator Works

Before covering the simple steps involved in draining your fuel filter’s water, it helps to understand what your fuel filter actually does. Modern Bobcat Tier 4 engines use an advanced multi-stage filtration system designed to protect the engine from contaminants, especially contaminated fuel and water.

Why Water Needs to Be Removed: Diesel fuel naturally attracts moisture. Over time, condensation forms inside the tank, allowing water droplets to mix with your fuel supply. If that water reaches the injectors or high-pressure fuel pump, it can cause corrosion, misfiring, power loss, stalling, or permanent system damage.

How the Fuel Filter Captures Water: Bobcat fuel filters use a proprietary paper material, engineered to separate fuel from water during the intake flow. As diesel moves downward through the filter, the material forces water to drop to the bottom of the housing, where it sits safely in the separator bowl until drained.

This system prevents water from ever reaching the injectors or pump, but only if you consistently drain it before the collection level gets too high.

Step by Step Guide: How to Drain Water from a Fuel Filter

Although Bobcat machines vary slightly by model, the overall process remains the same. Below is the recommended method for safely draining water from your fuel separator.

Step 1: Turn Off the Engine

Always begin with your machine completely turned off. Draining the separator while the engine is running may pull air into the fuel system or create unnecessary pressure.

Step 2: Locate the Fuel Filter and Fuel Drain Knob

Open the rear engine compartment to access the fuel filter. On most Bobcat Tier 4 machines, the fuel filter will feature a white or tan drain knob at the base. 

There are two filter styles:

1. Standard Filter Without Sight Bowl: Requires you to estimate when it's time to drain the separator
2. Filter With Clear Separator Bowl and Drain Valve: Allows you to visually check water levels and know exactly when draining is required.

Regardless of which one your machine has, the draining procedure is the same.

Step 3: Unscrew and Drain Knob & Allow Water to Flow Out

Place a small container or shop towel underneath the filter.

Gently turn the drain knob counterclockwise until water begins flowing from the bottom of the filter.

You’ll typically see water discharge first, followed by diesel fuel.

Once the fuel appears clean and free of bubbles, the separator is fully drained.

Step 4: Tighten the Fuel Knob and Close the Compartment. All Done!

Once the water has been fully drained from the fuel filter, screw the fuel knob back and properly close your vehicle’s rear compartment. Close the rear compartment, and your machine is ready to go.

Maintenance Tip: Drain Weekly for Best Results 

Even if your filter includes a clear bowl that shows water levels, many technicians recommend draining the separator once every week. The process takes less than a minute and prevents costly downtime.

In another one of our guides called 'when it’s time to replace your fuel filter', we recommended changing the fuel filter every 12 months or every 500 operating hours, whichever comes first. 

There you have it! We hope this guide was quick and easy. If you’re in the market for new parts for your Bobcat or Kubota, check out our catalog. We also carry the complete fuel system kits and are constantly adding new parts to our inventory.

The information provided in this article is for general guidance only. Always refer to your machine’s manual or consult a qualified mechanic before performing any maintenance or repairs.