I have not found a thermostat that will stabilize. They reach operating temperature, open and close... open and close; never consistant. Anyone know of a consistant thermostate for the bonneville?

Thanks!

??? That is exactly what a thermostat is supposed to do. It opens when the temperature gets too high, and then closes when it gets too low. It is constantly opening and closing to maintain the target temperature.

Did I misunderstand your question?

It just does it consently.

How can you tell the temp is fluctuating like that? Now that I think about it, most any thermostat I have kept tabs on has been pretty smooth.

On the tempo, that I had a mechanical temp gauge on, I can see the temp get up to about 200*, then the thermostat would open (a 195* unit), and then it would pin to about 190*. The only fluctuation would be if the car was not able to dissipate enough heat (sitting in traffic) and the coolant temp would start to rise until the fan kicked on (220*).

This makes me wonder, are you concerned about normal fluctuation from when the thermostat opens, until when the fans come on? If so, that has nothing to do with the thermostat, and everything to do with when the engine fans come on.

How can you tell it is opening and closing? If the coolant temp is fluctuating, what is it fluctuating from and to?

I'm curious myself. Anyway you can shoot a video of this sir?

I will try to get a video of it happening. It opens when it'* suppose to. As soon as it opens, it closes and the temperature drops... then it warms-up and does it again. I have gone through 2 thermostats that do this.

This is completely normal. Both of my L36'* and L67'* do this. In the summer time the temperature drop is not as quick as it is in the winter time. Again, this is normal.

On another note, at least the temperature is dropping vs going WAY up.

This is a normal condition. except your description is a little off. When the thermostat is closed the engine coolant temperature increases, not drops. A closed thermostat blocks flow to the radiator. An open thermostat enables flow to the radiator with the resultant cooling and drop in temperature.

Does the furnace in your house run constantly, or does it turn on when the temperature drops and off when the temperature increases, thereby maintaining a relatively stable temperature?

I have a similar, but reversed, problem

engine warms to about 200, thermostat opens, engine drops to about 110-120 and stays there - I've always thought the thermostat should close again, but this is second one and it runs so cold I have no heater

Is there a certain kind of thermostat I should get?

Are you saying you have replaced the thermostat twice now since your dilemma has started?