How To Diagnose A Failing Fuel Filter Housing

If you've got a Duramax diesel engine in your truck, you're probably familiar with changing the fuel filter. Occasionally a couple of other problems come up with the fuel filter housing.

In this diagnostic guide, you’ll learn how to recognize the most common signs of a leaking fuel filter housing. But first, we'll give a brief overview of how the Duramax fuel system works.

Duramax Fuel System Overview

Filter location

Image Credit: DieselWorldMag

From 2001 through 2016, Duramax powered vehicles had a fuel system that was different from most other diesel vehicles - they did not have a lift pump. Here's a brief description of the two types of fuel systems:

  • Conventional - Most diesel vehicles have both a lift pump and an injection pump. The lift pump moves fuel from the tank to the injection pump. The lift pump operates at relatively low pressure, approximately 30 to 60 psi. This creates positive pressure through the fuel lines and fuel filter. The injection pump then pressurizes the fuel to 30,000 psi or more before it enters the fuel injectors.
  • Duramax - The Duramax system does not have a lift pump. Instead, the injection pump sucks fuel from the tank. This creates a vacuum from the fuel tank through the fuel lines and fuel filter. Once the fuel reaches the injection pump, it is pressurized to the high pressures needed for the fuel injectors.

In most diesel engines, if the fuel filter housing leaks, fuel slowly seeps out. But, because there is suction at the Duramax fuel filter, when the housing leaks, air is sucked in.

How To Know When It’s Time To Check The Fuel Filter Housing

When the fuel filter starts to leak and allow air to enter, it causes some unique symptoms:

  • If the truck sits for a few days, it requires a lot of cranking to start.
  • The engine will start and then die.
  • If parked on an incline, the engine won't start unless it is manually primed.

If your truck is showing these signs, you probably have a leaking fuel filter assembly. But where is it leaking, and what caused that?

Why Is The Fuel Filter Leaking?

There are several places where the fuel filter assembly could leak:

The O-ring seals at the top and bottom of the filter can leak.

There are a few possible reasons why the fuel filter seals are leaking. They are usually related to something going wrong in the installation process. The fuel filter is usually installed from the bottom of the truck, and with poor lighting, it's easy to see how something could go wrong: Potential problems include:

  • The upper O-ring didn't seat correctly and was damaged as the filter was tightened.
  • The original upper O-ring was left in place, resulting in two O-rings being installed.
  • The original lower O-ring, at the Water in Fuel sensor, was re-used.

The Water in Fuel Sensor Failed

The Water in Fuel sensor is a plastic component that screws into the bottom of the filter. It can crack, especially when it gets older and brittle, allowing air to enter.

The Filter Head is Leaking

The filter head has several small seals. These are not replaced when changing the filter. As the truck ages, the seals can get dry and brittle, and then leak. The filter head can also crack, allowing air to enter.

How To Fix The Fuel Filter Housing

Fuel filter

If you think you've got a leak somewhere in your fuel filter assembly, the good news is that it is a pretty easy and inexpensive fix. Rather than troubleshoot to figure out exactly where the leak it, the simplest thing to do is replace the filter head, filter, and water in fuel sensor all at once. We stock all of those components. In fact, you can order a replacement OEM fuel filter housing from us at wholesale pricing. Do you have any questions about checking the fuel filter housing? You’re welcome to contact us!