OK, replaced both sensors last night. FYI (most of you probably already know this...I'm learning as I go...) the reason there are 2 sensors: one feeds to the computer (called the Coolant Temperature Switch) and the other goes to the temp gauge (called the ECT sensor or 'sending unit'). From the dealer the parts were like $22 and $40, from Auto Zone they were $14 and $31. There was a distinct "pop" when you get the new sensors pushed into place as the o-rings fit into their seals...a good sign. Hooked everything back up and pumped up the pressure test rig...all good.
Finished reassembly and started up the truck for a test drive. All good. Looks like this is the "correct" way to fix the problem of leaking ECT sensors.
OK, now that the job's done here's a couple of notes from my lessons learned:
1. After finishing the job, I don't think it was really necessary to replace the old sensors to fix the leak. As long as you can find the right sized O-ring to fit, I think that would have worked fine.
2. It's easy to notice once you have the new sensors to compare with how much the old sensor seals had compressed...I tried to take a picture but was lousy quality on my iPhone under low light (see below). Notice the difference in ring width between the new sensor (on the left) and the old sensor...no wonder it wasn't holding a seal!
3. You don't have to remove the intake manifold to complete this job, but it does make it a lot easier to access everything. I removed the manifold so I could see back to all the rest of the block while I pumped up the pressure test kit to look for leaks in other places, and took the opportunity to replace gaskets and clean the top of the block. It is possible, however, to replace the lower T-stat housing and sensors with the intake manifold in place.
4. Be very careful when removing the spring retainer clips around the sensors...they can fall down into some unbelievably small cracks if you lose hold of them! Thank god for extendable magnets and a good LED flashlight...
Hope this helps for anyone else trying to do this replacement.
