Procedures for Troubleshooting coolant loss:
Determine if the belt, the tensioner, and the water pump pulley can sustain the load of the vdf (fan) at 100% duty cycle without slippage: Look at the water pump pulley. If you find where the belt rides to be no longer black, but shiny and polished, that means that the belt has been slipping and that replacement of the belt, tensioner, idler pulley, and water pump pulley are warranted.
If the degas bottle is leaking you will see a white residue as it dries. This white residue is from the coolant. There are 4 likely causes for this.
1. Leaks in the Degas bottle itself, weak cap or imperfections with sealing to bottle.
2. Leaks in the coolant recirculation system (when checking for leaks, check the radiator hoses, heater hoses, EGR hose, Degas bottle recirculation and vent hoses, and the coolant filter system if applicable. Also check for a leaking seal around the water pump, block drain plugs, etc.).
3. EGR cooler starting to leak. An EGR cooler leak can cause the Degas bottle to overpressure and blow coolant out the cap (venting). This is often times (but not always) accompanied by white smoke out the tailpipe, and coolant under the EGR valve when inspecting w/ the vehicle parked on a decline.
4. Leaking headgaskets, typically from overboost. Leaking headgaskets can cause the Degas bottle to overpressure and blow coolant out the cap (venting).
Make sure that the hoses, degas bottle, and water pump gasket, block drains, etc. do not show obvious signs of leaking. If you are confident you have a leak to the ground (external leak), and that you do not have an EGR cooler or head gasket leak, then do a degas bottle pressure test. This can force coolant out of the system to where you can hopefully see it. Pressure up the system to 16 psig and look for leaks. Before the test, mark the coolant level. If you have a noticeable loss of coolant that you can not determine where it went, then evacuate the cylinders (remove glow plugs and rotate engine) before cranking.
After driving the vehicle and getting it up to temp, park on a down slope (vehicle nose pointed down) and pull your EGR valve. Look for coolant under the valve in the intake. Maybe 25% of the EGR cooler leaks can be identified this way.
Look for evidence of white smoke in the exhaust, and try to determine from smell if it is coolant. Also, white smoke from fuel will tend to rise and dissipate, where white smoke from coolant will tend to linger close to the ground.
Check the Degas bottle for any imperfections or leaks. Sand (with an emery cloth) the top face of the degas bottle opening. Consider replacing the Degas bottle cap at this point (part # 9C3Z-8101-B). They are cheap. I recommend the OEM cap. It is a reliable component for the most part. If at any time the Degas bottle cap has relieved, Ford states that the spring could be weakened and it should be replaced.
Next, let the engine cool down (you want a cold system to do this test). Apply vacuum to the cooling system with the coolant at minimum level or 1/2 inch below minimum. Vacuum type cooling system fillers work well for this. Try Snap-on RADKITPLUSA 078-00592 or similar. You can also use an Actron CP7830 vacuum hand pump - get a good rubber stopper for plugging the degas bottle cap opening. A #9 rubber stopper will work just fine. You can tee into the hose that goes to the Degas bottle from the intake and apply at least 25" of Hg vacuum to the system. Let it sit like that. If the vacuum does not hold over 15 minutes (preferably 20 min) you then need to pull the EGR cooler and check it for pressure and vacuum - out of the vehicle. If you change the EGR cooler, change the oil cooler at the same time and flush the system thoroughly.
It is possible to force coolant into a cylinder and cause a hydrolock by adding pressure to the degas bottle IF you have a significant EGR cooler or head gasket leak. For this reason the vacuum leak test is recommended to be done first. If the vacuum test above shows a leak, then it is time to do pressure and vacuum leak tests on the EGR cooler after removing it from the vehicle. If you decide to do the pressure test next, then be sure to evacuate the cylinders before operating the vehicle. Where a pressure test makes absolute sense to do (it is in the TSB) is when you are confident you have an external leak (hose, radiator, etc).
My next suggestion (assuming the cold vacuum test passes) for diagnosis is this: Get yourself a good pressure tester (I understand that Autozone sells a kit that works well) and tee into the smaller lines going into the degas bottle from the intake, do not remove the cap. Pressure up the system, record the release pressure of the cap, and look for leaks in the degas bottle itself and around the cap. If you have any leaks at the cap before it reaches 16 psi, AGAIN check the bottle for imperfections and verify that the top face of the degas bottle opening is flat and smooth. You may be tempted to do this pressure test first, but remember, there is a small chance that a pressurization of the degas bottle could force coolant into a cylinder if you have a significant leak in the EGR cooler already. Even a new cap has a slight potential of being bad. If the cap leaks at 14 psig or below, replace it again with a new cap and repeat this test.
Keep the pressure testing system mentioned above installed on your system and make sure your coolant level is at minimum. Loosen the cap on your Degas bottle and leave it loose (one round on the threads is good). Drive it until it gets up to temperature. Pull over and tighten your Degas bottle cap. Begin driving and CAREFULLY perform some WOT runs, getting the engine to maximum boost, but DO NOT EXCEED 28 PSIG boost (for those that might have a stuck turbo or are tuned and not studded). If the Degas bottle pressure varies widely, responding to engine throttle (ie quickly fluctuating between min and max) there is a good chance your EGR cooler is shot, especially if you see some white tailpipe smoke that may smell like coolant. Basically this test will tell you that something is leaking into the system to pressure it up. With the coolant already at operating temperature, there should be nothing that will generate a pressure in the degas bottle vent space.
If the EGR cooler is good (or you have just replaced it) and you have seen pressure swings in the degas bottle as tested in the previous two tests, then it is likely that you have a leak in the head gasket(s).
When replacing the headgaskets have the turbo taken apart and checked. The unison ring will typically be worn where the actuator runs. Fix the turbo as required.
If you want to use aftermarket parts the BulletProofDiesel parts are good. The BPD EGR cooler is very durable and has a good reputation. The BPD air cooled oil cooler is great also, just expensive. Anytime you have a failed EGR cooler, you should seriously consider replacing the oil cooler. At a minimum - be sure your ECT/EOT deltas are 15 degrees F or less at WOT (fully warmed engine).
If you don't have the means to diagnose this yourself, take it to a dealership/repair shop you feel comfortable with and have them test it.
FYI - The Lisle LIS20300 pressure/vacuum gauge will work (I believe it only goes to 14 or 15 psig though). O'Reilley's sells it.
Also - OTC 5613 Vacuum / Pressure Gauge Kit (0-15 psig)
Mityvac sells a 0-30 psig gauge and also does vacuum. It would be ideal: MVA6181
Lastly: KD Tools (0-15 psig) Model# KDS2521 and Actron CP7802 (0-15 psig)
DIY Cooling System Pressure Test Write-up.