I have a 95 deville 4.9. When I did my whole WP / timing cover job I also changed the thermostat.
I used a 195 degree failsafe. I've gone through two of these, both times they are getting stuck all the way open as if the car overheated. I've been watching my coolant temp and the hottest the dash readout ever gets is about 220, and that's only for a moment and it goes back down. From what I've read the rad fan doesn't even kick on until 230 ish. The car never seems hot after a normal drive. Yet after a few days the thermostat gets stuck open and the car won't go over 140, forget operating temp.
I know I'm installing it the correct direction but unless I got a pair of dud thermostats or these are not suitable for the normal temps of the car I'm confused. Two duds seems unlikely.
So what is the normal operating range of the 4.9?
Is this possibly too high for the thermostat I'm using?
What have ya'll used in the past that worked?
Anything I might be doing wrong here?