Every 15-17,500. You should drain the HFCM every oil change. Lower one can be fun. Drain HFCM [6mm allen key, you'll see the drain plug], put plug back in. A little dab of grease on that small o ring and threads helps ensure it comes out next time. Do not over-tighten. Remove cap and filter. You will see an index tab on the inside of the new filter. Insert new filter into housing, and while pushing in spin filter and you will eventually feel it seat. Then install new O ring on cap, then cap. You will lose about 1 pint or so of diesel. Have a drain pan handy. Its not bad after you've done it once or twice. Top one is simple swap. After changing cycle key on and off 3 times and thats it. Primes itself. Oh, BTW, its a good idea to wear something you don't mind getting messed up. Have fun.
