I just did the thermostat on my 99 D2 and I'm not sure what was in it honestly. I removed the lower radiator hose along with the fan shroud which makes the thermostat change out a breeze. Then I took my garden hose and ran water thru the cooling system until I saw the color go 100% clear. I let that drain as much as possible, re-installed my hoses, new thermostat, new stainless steel hose clamps, and I was able to get right at 2 4qt jugs of 50/50 coolant into the system. After properly doing a hot/cold cycle and a top off I was good to go.

The thermostat I tried was the OEM temp (was only 12.00 for a German made thermostat) it runs a solid no up/down temps of 204F down the road and 206F at idle. Of coarse I want it to be cooler, but I honestly like how steady of a temp it runs vs 188-200F which is a much wider range!

Dexcool being mixed causing damage is going to take a lot more of a ratio vs what you'll have left in there after draining/flushing it.

 

Best, I would have used full strength antifreeze and not the 50/50. Doing what you did got you to maybe a 25/75 mix in your system because you added 50/50 to a roughly equal amount of clear water. That may be just fine in Beaumont since you're unlikely to see below zero temps but it would be a problem in Minnesota, for example. Have you tested your resulting mix with a hygrometer to confirm the temp to which your system is protected?

 

Yes I measured it and I'm around -34 to -37 which the Prestone antifreeze tester said is recommended.

Tester could be lying but I tested it against 2 other vehicles I haven't touched and the coolant registered in just about the same area.

I at first thought I'd have to top it off with strictly 100% antifreeze, but after I tested it I just topped em off with the 50/50 stuff.