94 SC2 CTS replacement saga

At 172,000 I just had to replace the Coolant Temperature Sensor again. The usual symptoms. Temp Light on, check engine light on. The first time I had to change it was at 158,000 miles. So that one didn't last too long. An odd thing happened though as I tried to install the new one this time. I couldn't get it started in the threaded hole it goes in. Comparing it to the old one the old one was tapered a lot more. So I took a file to it and gave the first few threads a little taper. Now it went in ok. But then after starting the car it was much worse right away. Measuring the resistance of the new one after I took it out measured

0 ohms (a short). Not very good. This one was from autozone. So then I went to NAPA and got another one. This one also needed the file treatment to get it to go in. But now after starting theup car and letting it warm and and all it worked perfectly! Two weeks now so it must have fixed it. Sadly though when I went to look for the Autozone unit to return it I remembered that something fell out down toward the ground from the perch I put my tools on near the radiator. Sure enough it was the Autozone CTS. I never did find it! (I have a gravel driveway so its hard to find little things.

I had been trying to decide whether my problem was a thermostat or temperature sensor. I bought the Autotap scan tool which works with a program I run on my laptop. If you get it on sale, is about $100. This can read live data and showed CTS at 140F, which agreed with a thermometer applied to the heater core hose. Failed thermostat it was then. Autozone warranties its parts but I don't think that after you modify it, they would exchange it. With two sensors that were requiring filing to fit, one might think that the hole to which the sensor mounts should be re-tapped. I have an inexpensive set of metric taps and dies from Harbor Freight. They tend to be somewhat brittle so am always very gentle with them. Few things worse than breaking off a tap in the hole. (we do have a 'tap zapper' in our machine shop).

I too have a gravel driveway and use a sheet of 3/4" exterior plywood under my work area. Gives a decent footing for the floor jack to slide on. I also use a large sheet of cardboard around my work area. Nice to side on when creeping under the car... and it makes it much easier to find dropped tools and parts. The plywood stays put but the cardboard stays in the shed along with the ramps and jack stands when not being used.