I thought I would share my experience with changing the tensioners on my 2008 FX4. It has 147,000kms and 2 new Ford tensioners with crusher washers were installed (dealer order, packaging showed parts made in Italy). After reviewing multiple posts I decided to pre-tension in oil bath and then use vice to force some of the oil tension out to install. For the left passenger side I used a 27 mm socket. The original came out with no tension on the spring. Install easy and torqued to 47 ft lbs. The right top of the engine tensioner was much harder to get out and in. Had to remove TB, thermostat housing top, and temp sensor. The 27 mm socket would not fit, it was slightly hitting the intake manifold (probably could have fit if I had ground down the socket? but I didn't, it would have been a very tight fit) so I used the 27 mm wrench and loosened by hand. The original came out easy, tensioned and hard. Getting the new pre-tensioned one in was Difficult even after the vice loosening trick - I had to push down with a wooden dowel on the tensioner while hand threading. Once started it was a matter of hand and wrench tightening. PROBLEM; the crush washer kept falling down into the threads and binding. I had to hold it out of way with screw driver while threading. Used a couple of wraps of teflon tape around the washer before tightening down with wrench. No leaks on both tensioners upon warm-up. HOWEVER, upon test driving the engine made a sputtering noisy rattle for about 1/2 a block. Scared the **** out of me!! Shut her down, checked the engine (no visible leaks) and started back up... after about 20 seconds the engine noise stopped and no further problems...back to normal... what happened??!! After talking to my retired mechanic neighbor he said it was due to the pre-oiling of the tensioners causing a short term "hydraulic lock" preventing a delay in oil entering the tensioner under higher pressure. Supposedly a common occurrence if pre-oiled (?) and the reason why the tensioners should be installed DRY! What does everyone think about that? All-in-all the engine is working fine now and hopefully for another 150,000kms.

 

For all the threads I've read about the tensioners, the emphasis was always on avoiding cross threading.
Having to giggle about with a screwdriver and adding teflon tape makes that sound true.

Please describe how you applied the tape.
a) Did you go around the entire threaded body?
b) Did you just apply tape to hold the gasket in place?
c) Did you just wad some tape around the washer itself as you would to bulk up a loose ring on your finger?

Per-filling with oil rarely came up THAT I CAN RECALL.
Sounds like any air in the system has to be displaced by oil.
If I ever do this job on my 4.0 SOHC, I may partially fill the new tensioner with oil but I will crank the engine using the "clear flooded engine" method in order to drive the oil pump to fill the tensioners WITHOUT starting the engine.
I suppose installing them dry means one would just have to crank the engine longer.
Ask you neighbor about my idea.

 

Every time I replaced the tensioners, I did not pretension them. I had no problem getting them threaded in. The first time, I didn't use the "clear flooded engine" to get oil to the tensioners. The second time I did use the "clear flooded engine" to get oil to the tensioners. Both times I had no problem with rattling. Everything worked as it should.

My rear tensioner did not have a crush washer from the factory, and I reused the front one. I did put a very thin film of silicone on the rear one to help seal it. It worked and I had no leaks. The second time I replaced the tensioners I did a complete cam timing chain system rebuild and tried to order two new crush washers, but they were on National back order, and I could not get them. I again reused the front one and a thin film of silicone on the rear. That worked well again, and I am at over 305K miles with no leaks or rattles.

It is important to be careful about using silicone because the port that supplies the tensioner is near the sealing surface and getting anything in the tensioner could cause the tensioner to not work properly. Using that Teflon tape may have caused you rattling problem. A piece of it could have gotten into the intake port and/or the tensioner and interfered with the flow of oil. With Teflon taped being thin and compressive it may have eventually gotten pushed through the tensioner and allowed it to function properly again.