All fluids age, regardless of use, and become increasingly acidic with time. So front and rear differentials, transfer case, transmission and filter, and power steering fluid. You might also consider a complete gravity bleed of the brake system, too.
- Transfer case; 50 ounces of Mercon LV
- Rear Differential: 75W-140
- Front Differential: 80W-90
- Transmission: Mercon LV
- Brake System: DOT3 (The system will gravity bleed just fine. It just takes time, patience, decent music, a couple beers, and some aquarium tubing.)
- Power Steering System: Mercon LV. Pull the reservoir's bottom hose with a catch can under it. It's simple. If you do this every other oil change you will never need to replace the PS pump.
You will find - if the previous owner did not make modifications - that neither differential has a drain. You can use a suction device and get as much as 95% of the old fluid out, or you can remove the differential covers. Be advised that Ford does not merely seal the covers, they bloody glue them down. Removal of the rear cover is challenging, and exceptionally challenging in the case of the front cover. because physical access is so limited. The transfer case DOES have a drain. Amazing.
The transmission deserves a thread of its own and there are several here. Suffice it to say that Ford opted to use a "diptoothpick" that is so close to the exhaust system that thousands of mechanics all over America must have burn scars on the backs of their hands. The fill procedure is a two-step method, with the final level made when the transmission is at full operating temperature. And that's where the burns come in. A glove with 4 or 5 layers of duct tape across the knuckles will help. You will probably still get burned, but not as severely and you'll heal faster. Read up on the two-step fill procedure and crawl under the truck and familiarize yourself with what it'll take to do this successfully before you decide to do it yourself. Lots of us do, but I promise it fails the fun test.
Check the air filter and replace as needed.
Check the cooling system, drain and replace coolant if it's dark in color: Motorcraft Orange prediluted, PN VC-3DIL-B.
Changing the spark plugs can also be challenging. A good selection of extensions, wobble extensions, a u-joint, and a real good quality spark plug boot tool is necessary. The combination of extensions is different for each plug, so some good 3D problem solving is the order of the day. The top 8 are easy as long as the coils are okay. The bottom 8 plugs must be accessed through the wheel wells. The front right plug is right in line with the shock tower and is the most difficult to get to.
