most responders say that is how it should be. The part I do not understand is why is the temperature going up and down so much ~85 to ~100 driving vs idleing, why isn't the thermostat and all other components doing their job and maintaining a constant engine temperature. I also do see a yo yo effect after my water pump started leaking, before changing the water pump I do not think I saw that or I did not pay close attention. Before anyone says I need a new thermostat, This is my third theromstat after the water pump change.

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2010 ML350 Bluetec
2012 Mustang Convertible