Did you run the engine after adding stabilizer so as to have the fuel line and carb treated? I always add the stabilizer on my last couple of trips out so I know it is distributed everywhere it matters. Did you remove the t-stat? If it was cold and closed the antifreeze will just bypass it and go right into the exhaust. I also remove my impeller from the pump for inspection and install again in the spring. Also I remove the hose at the pump end (from the trans cooler) and let it drain, as it runs low under the engine it tends to hold water.
-Rich
1990 Supra Mariah/351 PCM 1:23-1 PCM