We know the fuel system on a modern common rail diesel is sophisticated, but the filtration on the Duramax is lacking. We are always looking for better filtration to keep these engines running optimally. Therefore, we put a 2-micron CAT filter on the stock filter head and have had great results; however, the CAT filter lacks water separation. So unless you are running a lift pump with a water separator, it is not advised to run the CAT filter. We have found an option for you that has better filtration and water separation. Donaldson fuel filters are a 3-micron fuel and water separator filter combo. It is 99% efficient at 3 microns and flows 90gph. It also features a built-in water drain on the bottom of the filter. Additionally, the Donaldson #553203 filter has a larger particulate capacity than the CAT filter, so we have taken our CAT filter adapter and substituted the underperforming CAT filter for the superior Donaldson filter.

Now we would like to explain the installation process of the filter head with the Donaldson filter. It is important to note that the spacer is required to ensure proper fitment with this filter.

Install Instructions

• This is the o-ring that comes with the filter adapter that is needed for the CAT filter; however, it will have to be removed for the Donaldson filter to seal correctly.
  
• The o-ring on the left is included with all Donaldson filters, and the o-ring on the right is the removed o-ring from the CAT adapter.
  
• Install the o-ring on the adapter.
  
• Start by removing the air intake tube to gain access to the filter head assembly.
  
• Next, loosen up the 12mm bolts that hold the filter head to the engine.
  
• Remove one bolt at a time and install the new longer hardware included with the spacer kit.
  
• Now install the spacer by sliding it over the new mounting hardware and tighten the bolts down.
  
• Furthermore, install the filter adapter to the filter head. When installing, lubricate the o-ring on the adapter with fuel and make sure the o-ring is seated properly. The o-ring should be seated in the groove of the adapter.
  
• Next, install the new Donaldson filter onto the adapter. Make sure to use some fuel or oil to properly seal the filter to the adapter. Once the new filter is installed, crack the bleeder screw on the filter head and pump the primer button. When fuel begins to leak from the bleeder screw, tighten the screw back up and pump the primer until it is stiff. Lastly, reinstall the intake onto the turbo mouthpiece and connect the MAF plug back in. Reinstall the inner fender and start the truck. If the truck starts and dies, just repump the primer and try again.