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Message: <blockquote data-quote="spack" data-source="post: 2082515" data-attributes="member: 69868"><p>My experience with engine temp ( stock 2018 raptor) is that when it transitions to cold outside, the engine goes from running hot in the warm weather to running hotter in the cold.  At temps in the neighborhood of freezing and below,  what is happening is the ambient air temp at intake becomes the overriding input which controls when to open the radiator shutters.  I have a video of them doing their calibration at engine start, wide open sweep, then closing...  And staying mostly closed, even when I load the engine and engine temp gets up to as high as 235F.  At that temp, the fans are howling and shutters are open about 1-5%.  Is this dumb?  Yes!  Lesson for me, the last thing I'd do is replace the thermostat.  No way that helps this situation.   It needs an ECM intervention.  Coincidentally, I had just flushed the cooling system and I thought for sure I had an air bubble in the cooling loop which was causing high temps.  But it coincided with a change in weather.  Took me awhile to get it together to put a camera up in the front upper grill to watch the radiator shutters.  Don't replace the thermostat.  At 200 degree and up engine temps, there is no difference between a 160 vs 195 degree thermostat.  That is not to say a thermostat change isn't useful for tunes.  But stock?  don't bother.</p></blockquote><p></p>