The K&N E-0644 is a washable, oiled-cotton drop-in replacement for the engine air filter in the 6.7L V8 diesel of Ford Super Duty trucks. The manufacturer describes layered, oiled cotton media engineered to improve airflow and capture contaminants, and designed to provide an increase in horsepower. It is built to fit into your existing factory air box, so no intake tube changes are needed. The manufacturer lists a No-Hassle Lifetime Limited warranty and filtration efficiency of up to 99%. Because the element is cleaned and re-oiled rather than replaced, it suits owners who want a lower long-term cost than repeatedly buying disposable OE-style filters.
Fitment is the first thing to verify. The manufacturer's catalog pages list the filter for 2017 through 2019 Super Duty trucks with the 6.7L V8 diesel, but other manufacturer-hosted pages show only 2017 and 2018, so confirm your model year before ordering. Performance claims are where opinions diverge. Owners on user forums are split: some report that it filters plenty good enough, while others argue that the turbo in these engines requires great filtering. Buy this filter for reusability and easy maintenance, not for guaranteed power gains.
The manufacturer's installation sheet states that the stock foam will not be used with the K&N filter. It also notes that K&N offers a replacement foam block (Part# 85-2003), for purchase separately. Owners on user forums debate whether the block is necessary, with some saying it mainly dampens intake noise.
Coverage is listed differently across manufacturer pages, with some showing 2017–2018 only. Confirm your truck's model year and engine with the manufacturer before ordering.
The filter is designed to be washed and re-oiled. The manufacturer's re-oiling amount is 8.3 oz (246 ml). Owners on user forums commonly advise rinsing gently from the inside with a slow stream of water, and some warn that improper cleaning causes problems.
Per the manufacturer's installation sheet, the job is a basic air box service with no modifications. Unclip the four clips and lift the air box lid to gain access to the air filter. Remove the dirty filter, then install the K&N filter by locating the features on the top of the air filter with the features on the air box base. Position the lid's inner flange into the filter's opening. Once positioned, push down to close the air box lid. Make sure the lid closes fully, because the manufacturer warns that the filter may not seal otherwise. Finally, the sheet recommends applying the K&N stop decal to indicate a reusable filter. Gotcha: diesel models have a foam block glued to the stock filter, so decide whether to buy the optional replacement block before you start.
