Do you experience a subpar heater? Mine really doesn’t put out much. I’ve heard this is normal for these things, but I’d like to check by taking an informal poll here.
Is your cooling system using Dexcool? If yes your heater core could be damaged by Dexcool.
I worked for GM in the late 90’s, we did not see a lot of heater concerns, Can’t remenber being briefed on heater concerns, there were plenty of other problems.
No Death-cool. I’ve had it since 88k, use normal antifreeze, no evidence of damage,
no problems except that the heater never seems to put out much heat. The thermostat is functioning correctly.