After discovering rust dust all over my serpentine belt and pulleys, I initially suspected the belt tensioner was the cause. It turned out the real cause was the common problem of the ac
clutch disintegrating but I only realized that once I removed the belt and could see down there more clearly.
In any case, when checking the belt motion while running, there was a lot of wobbling and I was also able to easily depress the belt which was enough to rotate the tensioner. So I elected to change the tensioner and belt at the same time.
At 104k or so, I was right at the mileage to change the belt. However given the fact that my Taurus has done plenty of short trips it has more hours on it than the mileage suggests, and it would have made sense to have changed the belt at the 10 year mark instead of almost 15 years and to have also checked the tensioner at the same time. Having a poorly performing belt and tensioner puts pressure on the other pulleys and in turn what they run. Repairing those other items is ultimately much more expensive. Additionally, a properly performing belt and tensioner means that overall performance improves. Most noticeably my alternator output is significantly up.
Having said that, for the 2004 Duratec, changing the belt tensioner is a bit of the pain so I thought I'd share how I did this.
What you'll need
1) Belt removal tool. I rented from autozone. A 90 day rental gives one plenty of time if you subsequently find other pulleys need to be changed.
The harbor freight version is less than $20 and will be even cheaper with a 20% coupon, so you may be tempted to own one.
2) Dayco 89281 tensioner or Motorcraft BT60. The Motorcraft is made by Dayco. My removed Ford one has Dayco stamped on it. I also used the Dayco because I got a good deal on a kit with both the belt and tensioner. The design of all other brands appears to have the benefit of a more convenient socket to place your belt tension tool into but they are also beefier and come with a new longer looking bolt. Being beefier would normally be a benefit, and the Gates one has a limited lifetime warranty, but given the limited space to get the tensioner in, I opted to not take a chance with a beefier tensioner and a likely longer bolt.
1) See attached removal instructions!
2) The instructions are somewhat incomplete and oversimplify the challenges of working in that tight area. If you have other tools eg ratcheting and / or offset wrenches, you might not have as many challenges as me.
a) Step 3: After removing the retaining nut, which is near the firewall, I wasn't able to move the top (low pressure) ac
hose out of the way despite what the instructions say. There is a bolt holding (the bracket that holds) the AC
Receiver Drier / Accumulator that needs to be loosened to allow the top ac
hose to move. This bolt and bracket are below the plastic bracket on the coolant reservoir that places and holds the coolant reservoir in the body. In order to access the bolt holding the Drier / Accumulator, remove the two bolts that hold the coolant reservoir in place, lift the coolant reservoir out a little and move it over an inch or so.
The top ac
hose in it's natural position is directly opposite the 10mm tensioner bolt and gets in the way of it's removal and replacement. When you need to get your socket or wrench onto the bolt especially during replacement, wedge something under the top ac
hose to hold it out of the way of the bolt. I struggled a lot on replacement before I thought of this simple idea.
b) Step 5: Because space is limited and the bolt is recessed, the serpentine belt tool with a socket can help you access and loosen the belt tensioner bolt. A thin enough ratcheting wrench would be helpful here. If an offset one fits then even better to get on the bolt in the first place.
c) Step 6: Replacement is not the same as Removal! The instructions call for placing the bottom (high pressure) ac
hose on top of the tensioner when removing. When replacing, it was impossible for me to hold the bottom ac
hose above the tensioner while simultaneously getting the tensioner back in. There was simply too much downward pressure. I ended up putting the bottom ac
hose back in it's regular position and it became far easier to hand thread the tensioner into position with no downward pressure on it. At this point, both the frame and bottom ac
hose are in the way of getting a socket on the tensioner bolt and there were a lot of turns to go with very little space to work in. I used a 10mm crowfoot wrench and rotated it with my fingertips of both hands to get the bolt in as far as possible. This saved a lot of time but the bottom ac
hose will remain in the way of getting a socket on the bolt. However, there will be enough space to again lift the bottom ac
hose up to put it on top of the tensioner. Then you can wedge up the top ac
hose to create the space needed for a socket on the serpentine belt tool or possibly an offset wrench to get the tensioner bolt fully tightened.
To give an idea of how tight the space is, once the bolt was in, I couldn't get a 1/4 inch drive torque wrench and socket onto the bolt to set it to the specified torque.
Although this job was a huge pain, I'm glad to have done it. Driving feels smoother and quieter, my alternator output is up and it's good to know there is no undue stress on the other pulleys and the components running off them. It also made me aware of the need to check both the belt and tensioner on other vehicles.
Hope this is helpful to someone.