2001 Chevy Impala Livid about Dex-Cool!

Yes there are many antifreezes out there that are ok for GM. I've seen them orange, clear, and green.
For them to refuse to work on it is naive.

About the sensor problem,
i don't believe that you had 2 bad sensors.
I either suspect the connection pigtail for the sensor.
Or
heaven for bid, the radiator is clogged up.

I suspect my news is not good, but lets start by clearing up some issues. All car engines are cooled with a mixture of 50 percent antifreeze and 50 percent water. That mixture is referred to as the "coolant". Up here in Wisconsin where it gets WAY below 32 degrees in winter, we need antifreeze in the coolant so the water won't freeze and crack the engine. YOU need antifreeze for the additives in it. That includes anti-corrosive agents and water pump lubricant. For your needs, the 50 / 50 ratio is relatively unimportant. That's why adding just water to the reservoir is perfectly acceptable. Up here, if we have to add on a regular basis, we might add just water one time, but then we would add straight antifreeze the next time to get the ratio back to where it should be.

The next issue is your observation that there's no coolant in the engine oil. Your entire story points to a leaking cylinder head gasket, and that shows up in one of up to about five ways. One of those is coolant leaking into the oil, but that is by far the least common symptom. Out of a hundred leaking head gaskets, perhaps two or three will include coolant in the oil. What is more common is to find a white, milky substance under the bottom of the "Oil" cap. That is usually caused by excessive short-trip driving where the condensed moisture in the oil settles on the cap because that is the coolest part of the engine. That alone will not cause a problem. The cure is to get out on the highway once a week for a good 20 - 30-mile run.

The additional clue is you've observed the need to add coolant on a regular basis. It has to be going somewhere. If it was leaking into the oil, the oil level would be going up.

The most common way a cylinder head gasket leaks is to leak coolant into one of the cylinders where it gets burned and goes out the tail pipe. When that gets bad enough, you'll see white smoke coming out of the tail pipe, and that can get real bad. When the leak is smaller, you won't see that white smoke, but you will continually lose coolant.

The next concern is the puddle under the front of the car. A head gasket can leak that way too, but the liquid should be red or green, not clear. A better suspect is that is clear water from the air conditioning system. The comfort comes from it condensing out the humidity in the air. That water collects in a drain pan in the dash, then runs out a rubber hose and onto the ground, just to the left of the right tire. That water is normal and desirable. The problem is there are also heater hoses in the same area, but those have coolant going through them, so if one of them is leaking, the puddle will be a color, not clear.

There's two tests to verify a head gasket is leaking. One is to use a special chemical tester at the reservoir to check for the presence of combustion gases, (exhaust gas), in the coolant. The second is to add a small bottle of dark purple dye to the coolant, then check later with a black light. The dye will show up as a bright yellow stain. If the head gasket is leaking, that dye will usually show up inside the tail pipe.

Replacing head gaskets is a fairly expensive job. In my city in the middle of Wisconsin, we have a lot of really reputable new-car dealers and independent repair shops, but we do have one well-known crook too. He owns multiple new-car dealerships. People avoid him and tend to go to the honest shops. We have all heard the stories about the dishonest shops, and for some reason almost all are in California. You will have the best luck if you find a shop you like, then form a steady relationship with them. Regular customers tend to be treated better because we live on repeat customers and positive word-of-mouth advertising.

An alternative, if time is not a concern, is to look for a community college with an Automotive program. We were always looking for live work to give our kids real-life experience. In fact, we had about two dozen community members who would sit on a broken car for months until it fit what we were teaching, because they understood the value it had for us. We charged ten dollars per hour for what the job was supposed to take, and we got parts at real good discounts, then marked them up ten percent to form a "breakage fund" in case we damaged something. The students were very respectful and well-supervised, but since they were only in the shop a few hours per day, it could take a few weeks to get your car back. That was the trade-off for the real low cost. Also, we only worked on what we were currently teaching, otherwise we were taking work away from the business owners who might hire our graduates. I only taught Engine Repair once a year, for eight weeks. Larger schools will likely teach that subject multiple times per year. Even if they can't do the repairs, they might be able to do the chemical test to see if my diagnosis is right. That test just takes a few minutes.