Cooling system

If it cycles up and down like that a few times before settling down, there needs to be a very small bleed hole drilled in the thermostat. That will let the coolant that is hot "over there" by the temperature sensor migrate to the thermostat "over here" so it will open up sooner. This symptom started on my '88 Grand Caravan many years after it was replaced. Drilling a 1/16 inch hole solved the problem. It's been in there over ten years now, and working fine. The original thermostat had that bleed hole in it already. The question was why did the new one work okay for a few years without it?

Caradiodoc